Civic VX Lean Burn Questions
 

I recently purchased a 1995 Civic VX with 120K miles on it. The car is a diamond in the rough and is 100% stock. So far I really like it and the FE has been respectable.

My first tank driving roughly 65mph on the freeway resulted in 43mpg with the correction for 175/70/13 tire size. From what I gather my FE could be better.

The previous owner had 175 size tires on the car at roughly 30psi and used 10-40W conventional oil. The tires were recently replaced with Sumitumo HTR T4 LRR tires at 50PSI at the OEM size. The ride and traction aren't too bad despite the high tire pressure. The spark plugs were replaced with the proper NGK V-power. Additionally, I'm planning to change the engine oil to synthetic 5-20W. Overall, the engine runs very well.

The clutch is getting replaced in the near future and the gearbox will be synthetic as well. I realize that the tires still need to break in, but I suspect this tank will be better than the last tank despite more city driving. I'm still getting used to the tall gear ratios as well.

I'm hoping to break 50MPG on a regular basis with mixed driving. The catch is that I have a California VX and from what I gather I'm losing roughly 4MPG. I suspect the CA VX does not run as lean in order to produce less NOx. I currently have a four-wire O2 sensor and would need to chase down a five-wire O2 as well as a 49-state ECU.

Is that all that I would need to change? If anyone has personal experience converting to the 49-state version I'd love to hear from you.

Have people had good success with monitoring their lean burn mode? I know it is easy to set something up with a multimeter, but I'm wondering how much it actually helps MPG-wise if you can watch when the car steps out of learn burn mode. Watching the number changed is one thing, but can you get results?

I'd to be interested to hear any other means of obtaining better mileage without significant effort and/or mods. At this point a boat-tail, pulse and glide, driving at a max of 40MPH, etc. would be difficult. I do glide down longer hills in neutral.

I look forward to hearing everyone's replies. I know there are a number of experienced VX owners on the forum!

Thanks!!

Welcome to GasSavers.

The Honda VX is a winner, even the California Version. I don't have a VX, but I have considered adapting my Civic. The conversion to a 49 state version involves the items you identified. I know in the HF's that they had a different transmission for the 49 state vs. California, as well as a high altitude version. I don't know if the VX also has different gearing or not.

The 5 wire oxygen sensor, using a voltmeter or something to monitor, does seem to enable people to better know when and how the car is going into it's lean burn mode. You could accomplish pretty much the same thing with a scan gauge or similar type tool, since your fuel use would drop significantly.

The down sides are: First the 5 wire sensors are a fairly rare item and probably as a consequence fairly pricey. The prices vary anywhere from $150-$350, leaning more towards the $350.

Second, the ecu, 5 wire sensor and lean burn modes seem to be pretty sensitive to a lot more issues with engine sensors and so forth, compared to the 4 wire sensor ecu.

You could, or should, in principal at least be able to pick up the 2-4 mpg difference, or at least some of it, if the transmissions gearing is different, if you were to change those things. I don't know if their are other items the 5 wire ecu might need, as well. Against that you have to trade off the cost of the 5 wire sensor, the ecu and the challenges of getting it to all run right.

In my perspective, unless your driving a phenomenal amount of miles, or unless you just want to do it, to prove to yourself it can be done, or you get some personal satisfaction from it, I don't think the mileage improvement can be justified, from a fuel savings standpoint. From what I've read on here about the 5 wire VX's, when they work they are great, when they don't it can get pricey and very exasperating.

Recently Installed LLR Tires Improve MPG
 

I'm still learning all the details that are involved with the 49-state swap. I would like to understand as much as possible before making a decision.

I did a little research and found a 5-wire O2 for $190 including shipping. Not too bad.

https://www.oxygensensor.net/l1h1.html

Additionally with the new LLR tires I averaged 49MPG across my most recent tank with a significant amount of city driving. A drastic improvement when compared to my 43MPG for the previous tank with lots of freeway driving. It turns out that tires do matter!

Does anyone have an idea of what an 49-state ECU costs and where one can easily be obtained? Does it matter if the car did or did not have air conditioning? My car has AC. I've heard they are fairly cheap given that turners pull so many of the engines.

I have a 49 states VX ECU for sale HERE

You can also check out the VX info thread in my signature below for more info.

Thanks! I had read a couple of the links, but missed a few good ones as well. I'll take a look at the ECU. Will any 49-state ECU work or are there details that I needed to be concerned with? I'm wondering how difficult it is work out the wiring for the five-wire O2 where it meets the ECU. Perhaps this addressed in your mentioned thread on the subject. The additional wire on the O2 side should not be too difficult.

I may have found a very good deal on a used five-wire O2 sensor. I'm wondering if O2 sensors tend to degrade with time or is it binary in the sense that it either works or it doesn't? :confused:

O2s degrade over time. When you see a sudden, 2-3MPG drop in mileage, it's time to change even though the O2 isn't setting a code yet. Called a lazy O2.

LRR tires are even more important once you get lean burn going. You can spend a lot more time in lean burn with the LRRs.

I responded in the VX ECU thread on the different versions. Basically that one I'm selling is from a 92-93 year VX and will work great for a 5 wire O2 change out.

Here is a 5 wire sensor. $371 tho. 5 wire oxygen sensor search on that page "5 wire" to locate it from the list.

>>If anyone has personal experience converting to the
>>49-state version I’d love to hear from you.

I converted mine. You need the 49-state ECU and and L1H1 off of ebay. Get the o2 wiring swap right though... check the other appends and you'l see the wiring connections. I promised a DIY but that never happended....

Check my gas log to see the difference it made.

With my old o2 sensor, my car would only run roughly in lean burn mode. i gained about 4-6 mpg with the new o2 sensor.
I think you can really feel lean burn kicking in. some people say you can't but if you really pay attention you can feel it kicking in and out. it will hesitate sometimes when you hit the gas in lean burn before going to regular mode. (i don't know why it only does it sometimes). but in general i have gotten all of the kinks out of the lean burn system and would fully recommend it.

Hardware Obtained
 

I recently obtained both a 49-state ECU and a used five wire O2. I just need to get the wiring worked out and I should be set. If someone could point me in the direction of the wiring details what would be great.

Ica13, it looks like you just converted your VX based on your gas log!

1 - Heater Positive -----------orange---------------Yellow/Black-----A6....-F
3 - Chassis Ground -----------yellow----------------Black-----------A23...-R
5 - ECM Ground---------------looped back to 7-----Green/White-----D22...-O
7 - Label Resistance Input-----looped back to 5-----White-----------D3....-M
2- Blank
4 - Cell Voltage Input---------red ------------------White/Blue------D8....-E
6 - Pump Cell Control---------white-----------------Orange/Blue-----D14..-C
8 - Reference Voltage--------black------------------Orange---------D16..-U

The list from another post..... you can use three of the wires from the existing O2 cable, the other 5 you have to find in the wiring harness near the battery (most are on the bottom connector). Don't rely on other's colors... find the appropriate wire by continuity check from the ECU harness to the engine compartment.

Beginning Conversion
 

Do you recall which three wires are the ones that are in the existing O2 harness? I suspect I should be able to figure it out by the color of the wires at the original 4-wire connector. Is that correct?

Also, I measured my resistor between pins 5 and 7 and got a value of 1.6Kohm which seems lower than the ~7Kohm I've read about. Then again it is a calibration resistor so perhaps mine was built on a Friday! :D

It is indeed a 5-wire L1H1. I understand that the resistor is inside the O2 sensor connector and simply connects from pin 5 to D22 and from pin 7 to D. The phrase "looped back to..." makes it a little confusing, but I think I have it under control. The looping back occurs inside the connector itself where the resistor is.

I'm headed to the wrecking yard tomorrow to attempt to find a 4-wire and a 5-wire connector so I don't have to cut either connector off. I would like to keep the car side and O2 side as untouched as possible.

When you guys tap into D14 and D16 to check the voltage is dropping into the lean burn mode (0.3v - 0.5v) how do you typically do this? Do you use a Viper connector down by the ECU or is there a slicker way without hurting the insulation of the ECU wires?

I'll be sure to check all wires back to the ECU pins out and not to depend on wire color.

Finding the 4-wire and 5-wire connectors at the junkyard proved harder than I thought.

Specifically I'm looking for a 4-wire from a bad O2 sensor and the 5-wire from the car's wiring harness. I need to dig up the 4-wire connector at a minimum.

Anyone have suggestions?

I did a little searching and I found a seller on eBay that sold converter connectors for Hondas with 5-wire O2 sensor (VX, CX) to 4-wire O2 sensors. Specifically those are not the connectors I needed because I'm going from a 4-wire configuration to a 5-wire.

However it turned out he had the connectors I needed and I got two 4-wire and two 5-wire connectors to my door in four days for around $20 including shipping. A reasonable price and extra fast shipping.

His eBay username Nigaphan should you need any Honda connectors.

This was a huge help being that I spent a full day at three different junkyards only to find one broken 4-wire connector that I needed.

I haven't seen anyone mention the necessity of using a shielded four-wire group as Honda did from the factory to stop RFI (radio frequency interference). I suspect that problems others have experienced are directly related to not knowing this fact.

When I built my harness for the '85 CRX VX I used an existing four-wire harness that was already on the VX engine. I changed the six-pin gray connector (C129) between the dash harness and the engine harness to a ten-pin connector, since they are readily available. This allowed the addition of D16, D8, D3 from the ECU connector, all shielded. The white, green/white and orange/black are used in both sensors. I made a jumper harness that would plug into the connector that normally plugged into the four-wire LAF sensor. The white wire, D14, is already shielded, you only need a three-wire shielded group for D16, D8, and D3. I found a five-wire shielded group off of another engine harness (from a '93 four-door Civic sedan), the wire group that goes to the distributor assembly. There is an eight-pin connector already attached. It even has the correct colors: orange/blue, orange, and white/blue. Doing it this way allows quick change of either LAF sensor and any of the ECUs. Additionally, it has the shielding ground loop already installed to ground at G101 on the thermostat housing. Be sure the ground is clean.

I was planning to use my own shielding configuration that I believe should take care of such issues. If I continue to have a problem with the set up that is from an unknown problem I'll be sure to look more into the OEM shielding. Thanks for the info.

I was thinking more about the O2 wiring swap. One very basic question I have is do I splice into the mentioned wires or am I chopping them and soley running them to the specified O2 sensor locations?

To my understanding there are three wires that I use from the original 4-wire O2 configuration and then something like four others that I have to find. I gather they are located by the battery in the stack of the four circular connectors. Once I identify the wires am I making a T-connection to the wire or cutting it and running it to the O2 sensor only?

I am unclear what these wires do when they are not being used for a 4-wire to 5-wire O2 sensor conversion.

Thanks!

Just in case you don't know: there are three plug-ins at the ECU that are used. The medium sized plug-in is referred to as the D plug. All the ECU wiring alterations you are going to perform happen in this plug, Looking at the wires coming out of the connector with the push button clip up, you count from left to right, top to bottom, one being the furthest to the left on top and two being just below it. Three is next to one, and so on.

Sensor input D14 is the one shielded wire that the 4 wire LAFsensor uses. It is orn/blu from ECU to C129, pin 6, six-pin gray connector on shock tower. Changes there into wht wire and goes to LAF pin 1 on the four-pin C111 gray connector. You will still use this wire. C111 pin 2 grn/wht wire is a sensor ground and it splices into other grn/wht wires and ultimately leads to D22. Pin 3 is the only one that you do not use. It is yel/blk in color and goes to the fuel injection wiring harness. Pin 4 orn/blk goes all the way to A6 heater control.

Wires you need to add: three wires that need to be shielded come from D3, D8 and D16. Yes, you have to run these wires all the way from the ECU. You need to get factory type plug-ins. On the 5 wire LAF sensor there is an eight pin gray connector, also called C111. A6 connects to pin 1; D14 connects to pin 7 and the grn/wht wire connects to pin 3. The four new wires: D3 connects to pin 4; D8 connects to pin 6; D16 connects to pin 8; and the last wire is an unshielded blk wire. It is a ground and grounds at the thermostat housing G101 and connects to pin 2. That is where all of the wires start from and go to. The shielding grounds at G101 thermostat housing, also.

In my case I went to the wrecking yard and picked up a new 4 pin connector with the correct plug-ins to interface with the already existing 4 pin connector that went to my 4 wire LAF. I plugged the three new wires into the three wires I retained in my existing harness. I just left an open socket (plugged with a little brown plug, of course) in C111, pin 3. The other end of the new wires went into the new C111 eight-pin gray connector in the aforementioned locations. The three new shielded wires (mentioned in the previous thread) were removed entirely from ECU to the distributor of a wrecked car. This allows the use of all of their existing ends and even the eight-pin gray connector that comes on the side of the distributor. This way they're all the correct length, and have all applicable plugs. Also, pick up a 10 pin connector, both halves, and replace your 6 pin connector C129 with it. This gives a great junction point for the new wires you are running.

Something else to note: If you choose to return to the four wire for smog reasons you can leave all of the wires connected to the ECU. There will be no interference. Once you disconnect your eight pin C111 connector it will just leave an open in the wires.

I'm new here. Please excuse me for barging in. Like Wandering, I have a CA VX that I want to convert to 49-state. Therefore I've been watching this thread with interest, and I appreciate the great info provided here by you and others.

soletek: "Wires you need to add: three wires that need to be shielded come from D3, D8 and D16. Yes, you have to run these wires all the way from the ECU."

Are you sure? Aren't those three (D3, D8 and D16) already present at C129? That's the impression I get from a schematic that was kindly posted by TomO (see here and here).

Maybe those wires are not present on your CRX (and therefore you had to run wires back to the ECU), but the schematic seems to indicate that they are present on every VX (and simply left unused on the CA version).

So I think all that's needed to wire the LAF (the new wideband 5-wire O2 sensor) is to create a special harness to run from the LAF to the shock tower. That is, from connector C111 to connector C129.

This would mean there is no cutting of any stock wiring, and no need to pass extra wires through the firewall.

Also, I think the needed harness could be ripped out of a junk VX (49-state). The tricky part is that it's bundled with a bunch of other wires. You'd have to remove the outer wrapping so you can leave behind the other wires and connectors you don't need.

Either that, or use the bundle (from the junk VX) as a complete assembly. This would create a result closer to a dead-stock 49-state VX, but it would require unplugging and replugging a bunch of connectors to other sensors. Not a huge deal, but it seems like a good idea to be able to switch back and forth between CA-mode and 49-state-mode. And that would be much easier if the old wiring bundle is left in place, and the new LAF connected with a separate harness.

I had suggested the possibility of using the complete wiring assembly from a junk VX (49-state). I'm realizing that's not a great idea, since that complete wiring assembly is the engine wire harness, which comprises about 30 connectors. It's probably not worth messing with so many connectors just to create a dead-stock result. It makes more sense to rip out the C111-C129 portion of that harness (taken from a dead VX). Or to fabricate new wiring that amounts to the same thing, maybe using cannibalized connectors.

For those of you that don't know, the VX is a fairly rare junked vehicle. Good luck to those who wish to find junked Vxs in the wrecking yard. I'm not saying you can't, but there aren't any around here. As for the wires existing in the under-dash portion of the harness, none of the harnesses, without 5 wire LAF sensors, that I have used have ever had those wires. Why would Honda have the harnesses built with extra componentry, at extra cost if only one vehicle type and model would be using that setup. That would not be cost effective.

If you do find a VX harness, don't think you can only pick up the engine portion. You have to get the under-dash portion (or modify one yourselves as I did).

Monroe74, the easiest way for you to find out if your wires exist is to look in the pin locations in Connector D as noted above. If they are a different color, don't expect them to go to the same place. Use a multitester, or the like, to see if there is continuity from the ECU end of each wire to C129. As for the accuracy of Honda literature, the schematic on page 24-5 of the 1994 and 1995 Electrical Trouble Shooting Manuals from tomo's post display the wiring of both CA and Fed versions, four and five wire. In both cases the book is wrong in one aspect and that is that it shows all seven wires running all the way to the LAF sensor on the 5 wire, when only five wires enter the oxygen sensor out of the seven. In the 1993 Electrical Troubleshooting Manual (on page 24-2), only the five wire is referenced (because they had no four wire VX versions up to that date), and is also misleading with the same information. Only the 1992 Electrical Troubleshooting Manual (also, on page 24-2) shows the correct wiring schematic. D3 and the grn/wht wire never truly reach the LAF sensor, and loop at C111, pin 4 and pin 3 (loop not shown in the book).

One of the first things any Honda Master Tech will say regarding the books is that they have errors. I learned this the hard way. Good luck!

sole: "the VX is a fairly rare junked vehicle"

Good point. I bet you're right.

"As for the wires existing in the under-dash portion of the harness, none of the harnesses, without 5 wire LAF sensors, that I have used have ever had those wires."

We're talking about what's called the main wire harness. My guess is that you were using harnesses from a model other than VX (like your CRX, for example). My belief is that the wires we're discussing are present in every VX harness (both CA and 49-state), but not in any other model.

Are you sure you ever ran into a CA VX harness that didn't have the wires?

"Why would Honda have the harnesses built with extra componentry, at extra cost if only one vehicle type and model would be using that setup. That would not be cost effective."

Good question. Here's an answer. We're talking about three wires that I think we agree are part of every 49-state VX. These wires are in the main wiring harness. On one end, they are found in connector C406, and connect to D3, D8 and D16 on the ECU. On the other end, they are found in connector C211, which is on the shock tower. From there, they ultimately connect (via the engine harness) to the 5-wire O2 sensor.

The question is whether these wires are also present in the main wiring harness of a CA VX (even though they have no use, in that model). I think they are. But why would Honda waste money including 3 wires that have no use? Because the CA VX was a small portion of overall VX production, and it would be a hassle to create a special main wiring harness just for the CA VX, with those wires deleted, just for the purpose of saving the cost of those three wires. It's simpler to leave them in, unused. Manufacturing is simplified any time a single part can be used in multiple models. Likewise for what happens down the road, when Honda is obliged to make replacement parts available on an ongoing basis.

Similarly, I think the rear wire harness on a VX has wires and connectors for a trunk light and rear wiper, even though those features were not offered on the VX.

"If you do find a VX harness, don't think you can only pick up the engine portion. You have to get the under-dash portion"

That's true, if someone is trying to put a VX engine into a non-VX body (like you did with your CRX). But I think you don't have to worry about the under-dash portion (the main wiring harness) if you already have a VX. And that's the situation Wandering and I are in.

"Use a multitester, or the like, to see if there is continuity from the ECU end of each wire to C129."

I agree with you that it's a good idea to verify that the wires go where I think they go.

"In both cases the book is wrong in one aspect and that is that it shows all seven wires running all the way to the LAF sensor on the 5 wire, when only five wires enter the oxygen sensor out of the seven."

I understand your point. I agree that the drawing is confusing, but it makes sense once you realize that the calibrating resistor is housed in the C111 connector itself, rather than in the body of the O2 sensor.

"they [the books] have errors"

I'm sure they do. But likewise for comments people write on forums like this! Anyway, I intend to take your advice and verify (with some kind of continuity tester like a multimeter) that the wires I see on the shock tower (at C211/C129) actually go where I think they go.

Thanks for the numerous pieces of useful information. I think I have a pretty fairly good idea of how the conversion is performed. If I can pull it off I plan to put together a DIY. I'm going to give it a go this weekend.

As questions arise support would be appreciated!

Support
 

I'd be very happy to help you. Just send a PM anytime.

I think I've made some progress in figuring out the wiring (as far as converting my CA VX to 49-state). I haven't fully installed and tested this yet, but I've done a bunch of tracing and continuity testing, so I think it will work. But hopefully someone can tell me if it looks like I've made any glaring errors.

My goal is connect the new parts (ECU and O2 sensor) without cutting any existing wiring. I want to do it all via standard Honda connectors, so the installation will be easily reversible, without a trace.

Three ECU terminals (D3, D8 and D16) are used in the 49-state VX, but not in the CA VX. The good news is that the CA VX already has the needed wires in place in the main harness (at least this is true in my '95 CA VX; I verified this with a continuity test). This means if I create a custom harness, using 4 connectors, I can install the new O2 sensor without cutting any wires.

I was able to find the needed connectors at a junkyard. I didn't need to find a VX; the needed connectors are used in a bunch of different places on the other '92-'95 Civics. The needed connectors are as follows:

8-pin female
6-pin male
6-pin female
4-pin male

You create your custom harness by wiring them together as follows:

8-pin female.
pin 1 needs to be wired to 4-pin male, pin 4.
pin 2 needs to be wired to ground, G101.
pin 3 needs to be wired to 4-pin male, pin 2.
pin 4 needs to be wired to 6-pin male, pin 3.
pin 5 is not used.
pin 6 needs to be wired to 6-pin male, pin 2.
pin 7 needs to be wired to 6-pin male, pin 6.
pin 8 needs to be wired to 6-pin male, pin 5.
The wires from 4, 6, 7, and 8 need to be shielded, and the shield should be grounded.

6-pin male.
pins 2, 3, 5 and 6 are referenced above.
pin 1 needs to be wired to 6-pin female, pin 1.
pin 4 needs to be wired to 6-pin female, pin 4.

6-pin female.
pins 1 and 4 are referenced above. pins 2, 3, 5 and 6 are not used.

4-pin male.
pins 2 and 4 are referenced above. pins 1 and 3 are not used.

That's a total of eight connections that have to be made, to join these 4 connectors together to form your custom harness. (There's one more connection, a ground, that will be made when you're installing the harness on the car.)

The harness is installed on the car as follows:

8-pin female. Connects to new O2 sensor, C111.
6-pin male. Connects on shock tower, to female of C129.
6-pin female. Connects to male of old C129.
4-pin male. Connects to old C111 4-pin female (the connector your old O2 sensor was plugged into).

The following is reference information. It's stuff you don't really need to know. It's the wiring instructions, with extra information that could be useful if you want to know more about what's really going on. Or if you need to trace things for troubleshooting purposes.

8-pin female.
pin 1 needs to be wired to 4-pin male, pin 4. This line goes via C103, pin 2, and ultimately reaches A6.
pin 2 needs to be wired to ground, G101.
pin 3 needs to be wired to 4-pin male, pin 2. This line goes via C103, pin 9, and ultimately reaches D22. A6 and D22 were in use in connection with the old O2 sensor, so we're taking advantage of the existing plug and wiring.
pin 4 needs to be wired to 6-pin male, pin 3. This line goes via C129, pin 3, and ultimately reaches D3. The old O2 sensor did not use D3. But we're taking advantage of the fact that C129 already is connected to D3, even in a CA VX.
pin 5 is not used.
pin 6 needs to be wired to 6-pin male, pin 2. This line goes via C129, pin 2, and ultimately reaches D8. The old O2 sensor did not use D8. But we're taking advantage of the fact that C129 already is connected to D8, even in a CA VX.
pin 7 needs to be wired to 6-pin male, pin 6. This line goes via C129, pin 6, and ultimately reaches D14. The old O2 sensor did use D14. So we're reaching D14 via C129, pin 6, just like the old O2 sensor did.
pin 8 needs to be wired to 6-pin male, pin 5.This line goes via C129, pin 5, and ultimately reaches D16. The old O2 sensor did not use D16. But we're taking advantage of the fact that C129 already is connected to D16, even in a CA VX.

6-pin male.
pins 2, 3, 5 and 6 are referenced above. Those pins connect the O2 sensor to the ECU.
pin 1 needs to be wired to 6-pin female, pin 1.
pin 4 needs to be wired to 6-pin female, pin 4.
Pins 1 and 4 connect the EGR to the ECU. See below.

6-pin female.
pins 1 and 4 are referenced above. pins 2, 3, 5 and 6 are not used.
This connector, with those two connections, is needed to take care of C130, the EGR valve. It's wired via C129. Since we're interfering with C129, we're essentially providing a jumper so the EGR is connected exactly as before.

4-pin male.
pins 2 and 4 are referenced above. pins 1 and 3 are not used.
This connector allows the new O2 sensor to reach A6 and D22 in exactly the same manner that the old one did.

A few minor corrections/clarifications with regard to my terminology.

I said the new 8-pin female connector (in the custom harness) "connects to new O2 sensor, C111." That's basically correct, except that I should be more careful with the way I use the term "C111." I was implying that C111 is the male connecter that's wired to the O2 sensor. It's not. C111 refers to the female connector that mates with the male connector that's wired to the O2 sensor.

Also, as you look at various drawings it might be helpful to keep in mind that C111 can be either a 4-pin female connector or an 8-pin female connector. It's the former in CA and the latter in the other 49 states.

I made a similar mistake when I said this: "6-pin male. Connects on shock tower, to female of C129." Actually, "C129" is the name of the 6-pin male. The female counterpart (mounted on the passenger-side shock tower) is called C211.

I made a similar mistake when I said this: "6-pin female. Connects to male of old C129." I should have said "connects to old C129, which is a 6-pin male connector."

In other words, the new custom wiring harness has a new C129 and a new C211. The former attaches to the old C211 and the latter attaches to the old C129. You can think of these two new connectors as being a jumper between the two old connectors.

The other two connectors on the new custom wiring harness (the 8-pin female and the 4-pin male) act in a similar manner. You can think of them as a jumper between the new O2 sensor and the old C111 that the old O2 sensor used to be connected to.

Another minor correction. I said this: "we're taking advantage of the fact that C129 already is connected to D3, even in a CA VX." It would have been clearer and more correct to say "C211," not "C129." The latter is a male which plugs into the former.

I do the same thing in a few other places (refer to C129 when it would have been more correct to say C211).

Monroe74, it sound like you are making lots of progress.

I quickly read over your spiel and I'm a little unclear how you are interfacing with the new 5-wire O2 sensor. I saw that you purchased a 4-wire connector from the junkyard (like the one on the CA O2 sensor) but I didn't see any mention of the 5-wire connector that is normally on a 49-state car's wiring harness. This would be used to interface to the 49-state O2 sensor.

That said I don't have all of the connector CXXX's memorized so it could be in there. From what I gather you can't cut the connector off the 5-wire O2 sensor because the calibration resistor is physically inside the connector housing. With the 5-wire connector I had a difficult time finding it and ended up purchased it from the mentioned eBay user in a earlier post in this thread. I had no luck at the junkyard with that particular connector.

"it sound like you are making lots of progress"

Thanks for your kind words. I started out by finding lots of helpful information in posts by you and others, here and elsewhere. It was nice to not have to start from scratch.

"I saw that you purchased a 4-wire connector from the junkyard (like the one on the CA O2 sensor)"

Yes. To build the custom harness, I grabbed 4 connectors from a junkyard. One of the 4 connectors is a 4-pin male, and it is identical to the connector that is wired to the CA O2 sensor that was put on my car in the factory.

I need this 4-pin male so I can connect my custom harness to the 4-pin female (C111) that used to connect to the old O2 sensor. This 4-pin female has value because it gives me a way to reach A6 and D22.

"I didn't see any mention of the 5-wire connector that is normally on a 49-state car's wiring harness. This would be used to interface to the 49-state O2 sensor."

There is no 5-wire connector that is relevant to this discussion. The 49-state sensor does not have an 5-pin plug. It has an 8-pin plug. Those 8 pins are accounted for as follows. 5 pins are connected to visible wires that travel to the sensor housing (that's why it's commonly described as a "5-wire" sensor). Two of the pins are attached to a resistor that is hidden inside the male connector itself. One pin is unused.

"I don't have all of the connector CXXX's memorized so it could be in there."

It's easy to get confused. I recommend this schematic, to help you picture what's going on. I also recommend not paying too much attention to colors. Instead pay attention to the pin numbers in each connector, and then you can visualize the path between the O2 sensor and the ECU.

But I think my post above has all the information needed to do the wiring, and understanding the reasoning and the details is optional.

There are aren't that many connectors that you need to know about. Consider the CA car before we start changing things. There's a 4-pin male wired to the O2 sensor. This plugs into a 4-pin female, C111. C111 is part of the engine wiring harness. Those 4 wires from C111 go to various places, but what's most relevant is that one wire goes to C129. This is a 6-pin male, which plugs into C211. C211/C129 are on the passenger-side strut tower. C211 is part of the main wiring harness. It has 4 lines that run to the ECU. A CA car uses only one of those lines. A 49-state car uses all four.

To install the custom harness I described, you need to unplug C129 from C211. Then the 4 connectors on the custom harness attach to C129, C211, C111, and the new O2 sensor. And there's a ground connection, for the shielding. That's it.

Aside from swapping the ECU, these are the only connectors you have to mess with. And there is no need to cut any stock wiring, and no need to run new wires through the firewall to the ECU.

"From what I gather you can't cut the connector off the 5-wire O2 sensor because the calibration resistor is physically inside the connector housing."

Yes, there is a resistor hidden inside that particular connector. But I have no idea why you would have an interest in separating that connector from the sensor. I don't see what you're trying to accomplish by doing so.

"With the 5-wire connector I had a difficult time finding it and ended up purchased it from the mentioned eBay user in a earlier post in this thread. I had no luck at the junkyard with that particular connector."

As I said, it's not a 5-pin connector (wired to the 5-wire sensor). I don't see how a 5-pin connector is going to be of any use to you. It's an 8-pin connector. And to work with the 49-state O2 sensor, you definitely need an 8-pin female connector, to accept the 8-pin male that is wired to the sensor.

This 8-pin female that you need is not hard to find. For example, C125 will do the job (see page 23-17 of the service manual). I think C125 is present on every '92-'95 Civic. And I think the connector will most likely be there even if the engine has been ripped out. And it's in a spot that's easy to reach.

The other three connectors needed to build the harness are similarly easy to harvest.

Conversion Complete!
 

Last night I completed the CA to 49-state VX conversion. It took most of the night, but I was able to get it done in one aggressive evening. According to the lean burn monitor voltages it is working correctly. I'm getting the suggested voltage at startup, warm idle, and lean burn cruise.

Does anyone know what the estimated mileage is at roughly 65mph in learn burn mode? Is there any transfer function between the lean burn monitor voltage and miles per gallon?

The lean burn mode is surprisingly robust. I drove it a bit more today and found I was able to climb light hills at 70mph without it dropping out. It is also very quick to get into lean burn mode. I found I was able to get into it even on surface streets in fourth gear between lights if I was gentle on the throttle.

With two connectors and a couple extra connector pins I was able to do the install without cutting any of the OEM wiring. This allows me to easily regress to the original configuration if desired.

The wiring was an initial concern and then if I did get it wired correctly there was question about the used 5-wire sensor I had purchased. It was in good condition but I have heard of people having problems because they didn't know if it was the wiring or the sensor or the ECU for that matter.

Everything appears to be working well in my case and I just filled up the fuel tank so we'll see how the mileage is. I'll keep everyone posted if any problems should develop.

A DIY document is to follow. Thanks everyone for the support. Eco-tuners unite! :thumbup:

Wandering, congratulations! That's excellent news.

I'm very interested in knowing how you did the wiring with just two connectors. I can see how to do it with four, but if there's a simpler way to do it I'd love to know what it is.

I'm realizing that folks reading this thread might be confused by the fact that two different numbering systems are being used, to refer to pin (terminal) locations in connectors.

The connectors we're discussing are not physically marked with pin numbers. So one has to adopt a convention to refer to the pins by number. Trouble is, different conventions are being used.

When I refer to pin numbers in my posts here, I'm using the same convention used by Honda in their service manuals. That convention is expressed in this illustration. (By the way, in that illustration the term "locking device" is a reference to the device that clips the male and female connectors together. It is not a reference to the device that clips the female connector onto a mounting bracket.) Once you understand that illustration, you can follow the pin numbers that are used in schematics like this.

Other folks have posted comments (in this thread and elsewhere in this forum) which contain very helpful information, but which follow a different numbering convention, for some reason. An example of such a comment is here.

The convention implied in that post is that the locking device is facing to the left, instead of facing up. And that you are looking at the back of a male connector. Pin numbers in the Honda manuals follow the convention of the locking device facing up, and that you are looking at the front of a male connector (as expressed in the illustration I cited).

For example, that post indicates that the unused terminal (on the 49-state sensor) is pin 2. But the schematic I cited indicates that the unused terminal is pin 5 (it indicates that by omission). The point is that pin 2 and pin 5 are the same pin, depending on which way you hold the connector when you start counting pins.

This had me confused until I realized what was going on.

Oh yeah, one more thing. Just to make things interesting, Honda uses a different numbering system (different from the two I've already described) with regard to the 3 plugs that attach to the ECU. The numbering system for those connectors is illustrated on page 11-25 of the service manual.

But that information is not essential to the conversion, because although you need to swap the ECU, there's no need to fuss with individual pins or wires down at the ECU.

Wandering, I just figured out the answer to the question I asked you. I couldn't understand how you did the job with just two new connectors. Now I realize that you mentioned using extra connector pins. So I guess what you did is you altered C129. When your car came out of the factory, that connector had 3 blank positions (pins 2, 3 and 5). You filled in those blank positions with new connector pins. This gives you access to D8, D3 and D16 (respectively), which were wired (at the factory) to C211 on the shock tower.

I assume you wired your three new connector pins to a 3-wire shielded cable that runs to the vicinity of C111. At that end, you have the other two connectors I mentioned: an 8-pin female and a 4-pin male.

Your approach has the appealing simplicity of not needing those two extra connectors (the six-pin male and six-pin female which are required with my solution). I never thought of doing it that way because I don't know how to add pins to a Sumitomo connector. I think you need fresh pins and seals. I wonder where you got them from.

Maybe you got your hands on a kit like the one illustrated towards the bottom of this page. (By the way, that page illustrates yet another numbering system different from all the other ones that have been discussed so far.)

One advantage of my approach is it's easier to reverse the conversion without a trace. Your approach is very reversible, but your new harness stays in place (and with unmated connectors that are potentially subject to corrosion, unless you protect them somehow). But I think this is a very minor consideration.

In Summary...
 

Good deduction! You are correct!!

Once you get your head around the wiring details the conversion is "fairly" straight forward.

You'll need the following Honda hardware:
49-state ECU https://www.gassavers.org/showthread.php?t=2151
L1H1 5-wire O2 sensor

There are seven wires total that need to be accounted for. The break down I used was derived and simplified from the past table that was posted on the subject. See above.

Contained within the original CA O2 sensor connector are three wires that are utilized.

FIRST THREE WIRES:
ECU A6 - O2 sensor pin 1 (orange)
ECU D22 - O2 sensor pin 5
ECU D14 - O2 sensor pin 6

To clarify as an example ECU A6 means pin 6 on the A connector of the ECU. Generally speaking A is the biggest, D is medium, and B is the smallest ECU connector. Pin 1 is in the top left with pin 2 directly below and pin 3 is one to the right of pin 1. See link for details: https://www.gassavers.org/showthread.php?t=2427

On the O2 sensor connector pin 1 is similarly in the top left and for an OEM 5-wire L1H1 O2 sensor pin 1 is orange. The same pin numbering nomenclature is used on this connector as the ECU.

SECOND THREE WIRES:
ECU D3 - O2 sensor pin 7
ECU D8 - O2 sensor pin 4
ECU D16 - O2 sensor pin 8

All three wires are in the bottom circular connector on the shock tower. On the half of the connector farthest from the firewall there are three rubber plugs in the pin holes and no wires coming out. The opposing side of the same connector closest to the firewall is fully populated with wires. There are the three required wires!

Disconnect the connector with the three rubber plugs. Pull out the three plugs with a small pair of pliers. Remove the white piece of plastic on the inside of the connector using the same pair of small pliers to gently slide it out. Now you have access to the pins. From the back of the connector slide in pigtailed connector pins from a donor connector that has been taken apart in a similar fashion. At this point three pieces of wire will be coming out of the reassembled connector. These will need to run from the shock tower to the O2 sensor connector.

Keep the plugs if you want to change back to the original configuration. Take the connector apart and remove the added pins then reinstall the plugs.

FINAL WIRE:
ECU A23 - O2 sensor pin 3

For the seventh and final wire I simply wired it to a chassis ground location. I checked continuity back to A23 on the ECU and it worked great.

I used two connectors to make an adapter from the factory CA 4-wire O2 connector to the 49-state 5-wire O2 connector. At this junction I spliced in the four wires including the ground to the proper locations going inbound to the O2 sensor connector pins from the shock tower. I connected the chassis ground to the shock tower.

Focus on connecting pin numbers on the ECU to pin numbers on the O2 sensor. The colors of wires between are different on different vehicles and for me it tended to complicate the process.

Before testing the car be sure to do multiple continuity checks from the ECU pins to the O2 sensor. The suggested wire mapping appears to be correct so be cautious if it doesn't check out with a multimeter.

I've tried to simply the conversion so please let me know if I left any important details out.

Wandering, thanks for those very helpful details.

I'm going to summarize some key aspects of my approach, compared to your approach. There are some interesting similarities and differences.

As I mentioned before, I think readers should be warned that two conflicting numbering systems are being used. Consider the plug on the 5-wire sensor. If I hold that plug in my hand, facing the pins, and with the locking device facing up, I number those pins as follows:

1-2-3-4
5-6-7-8

Contrast this with the way you're numbering them (and some other folks here have also used this numbering system):

1-3-5-7
2-4-6-8

It's not a problem if a reader is aware and knows how to translate between the two. In other words, when I say pin 7, and you say pin 6, we're actually talking about the same pin. I'm counting left-to-right, whereas you're counting up-down.

Your system makes sense because it's the system Honda uses in numbering the ECU pins. Trouble is, they use a different system for their other connectors, like the various connectors we've been discussing. So you need to do it my way if you want to understand Honda schematics (like the one I cited a couple of times above).

Speaking of pin numbering, I want to warn readers about ECU pins. You referred to an illustration that numbers them as follows:

D1-D3-D5-D7-D9-D11-D13-D15-D17-D19-D21
D2-D4-D6-D8-D10-D12-D14-D16-D18-D20-D22

That's correct, provided you're facing a male connector (that is, the pins on the ECU itself). But someone testing continuity is facing the female connectors on the end of the cable. That means you're dealing with a mirror image, and the numbering needs to be reversed, like this:

D21-D19-D17-D15-D13-D11-D9-D7-D5-D3-D1
D22-D20-D18-D16-D14-D12-D10-D8-D6-D4-D2

Something else about pin numbering. Take a look at this schematic. The D portion of the ECU is connected to the main wiring harness via a connector called C404. The schematic indicates, for example, that ECU terminal D8 is connected to pin 15 on C404. When you think about it, you realize that Honda is numbering C404 as follows:

1 -2 -3 -4 -5 -6 -7 -8 -9 -10-11
12-13-14-15-16-17-18-19-20-21-22

Remember that C404 is female, so those numbers are interpreted with the connector facing away from you (as portrayed in this illustration). Notice how C404's pin 15 is in the position that corresponds with D8.

It's interesting to notice that the convention Honda uses for numbering ECU pins is not the same convention it uses for numbering pins on the connectors that attach to the ECU. On those connectors it used the same left-right (rather than up-down) system it uses throughout the vehicle.

I find it very helpful to use the Honda schematics, and I find that it helps to have a firm grasp of the pin-numbering conventions. So that's why I figure this is worth explaining.

Anyway, we've both made this important observation: all the wires needed to hook up the 5-wire sensor can be found under the hood. There's no need to run wires through the firewall to the ECU. Honda has already done that for us.

In particular, all the wires we need (aside from a ground) can be found in two places: the C111 connector (the 4-pin jack that served the original 4-wire sensor), and the C211/C129 connector. The latter is found on the passenger-side shock tower. On that tower, there is a mounting bracket that holds four sets of connectors. The connector pair at the very bottom (closest to the ground) is C211/C129.

C211 is the female side. It's part of the main wiring harness, and it has wires that run to the ECU. C129 is the male side. It's part of the engine wiring harness. These are 6-pin connectors. On a CA VX, three of the C129 pins are blank. These are the pins you and I both tap into (you do it by modifying the original connector; I do it by providing a new connector to replace the factory C129).

In both your solution and my solution, pin 4 (on the L1H1) reaches D3 (on the ECU) via pin 3 of C129 (I'm using my pin-numbering convention, not yours). And pin 6 (on the L1H1) reaches D8 (on the ECU) via pin 2 of C129. And pin 8 (on the L1H1) reaches D16 (on the ECU) via pin 5 of C129.

Similarly, in both your solution and my solution, pin 1 (on the L1H1) reaches A6 (on the ECU) via pin 1 of C111 (the jack that served the old O2 sensor). And pin 3 (on the L1H1) reaches D22 (on the ECU) via pin 2 of C111.

And in both your solution and my solution, pin 2 (on the L1H1) is connected to ground.

We take a slightly different approach to pin 7 (on the L1H1). We both connect it to D14 (on the ECU). You achieve this via pin 1 of C111. I achieve this via pin 6 of C129 (they amount to the same thing). In other words, you run 3 wires to C111, and 3 wires to C129, whereas I run 2 and 4.

Finally, you alter C129. What I do instead is use two extra connectors. This allows me to tap into the C211/C129 connector pair, without altering any existing wiring or connectors.

Why do I need two extra connectors, and not just one? Because the C211/C129 connector pair has a dual purpose. It doesn't just support the O2 sensor. It also supports the EGR valve. So my 4th connector is needed to maintain continuity to the EGR valve.

But that's a background issue that doesn't really need to be understood. I think my earlier instructions (for how to wire the 4 connectors) are accurate and sufficient. I'm more confident about that, now that I have confirmation from you that your C211/C129 connectors are wired to the ECU the same way mine are. I think we've both done a lot of continuity checking and come up with identical results. Also, what we've discovered is consistent with a bunch of different Honda schematics I've looked at (including, especially, the one I cited a few times).

One more thing. In the spirit of trying to reduce confusion, I want to mention that L1H1 has lots of names. Folks might not realize they mean basically the same thing:

5-wire O2 sensor
49-state sensor
L1H1
wideband sensor
LAF (linear air/fuel) sensor
UEGO (universal exhaust gas oxygen) sensor
Honda part number 36531-P07-003
Bosch part number 13246 (which is a repackaging of NTK's L1H1, and which is not to be confused with the Bosch LSU4 series, which is also a wideband sensor but not interchangeable with L1H1)

Hi Wandering and Monroe,
Where are you two located? I bought the parts to do the conversion last year Nov-Dec, but never got around to doing it. With gas hovering around $4/gal, I want to get going on this project.
Gary

I went to two junkyards with no luck. I tried the big one in moss landing, no go. What additional connectors do I need? I just read the entire thread and am a bit confused as whether or not we need new connectors. I always thought I had to run wires into the car, but it seems like I don't.

Hi Gary.

"Where are you two located?"

I'm in the Northeast. I think you're in CA. But I would be glad to try to help you remotely.

Will your car still be legal in CA, if you do the conversion? That's a question you would have to ask someone else. But my methodology is pretty reversible, so it would not be hard to cheat.

"I went to two junkyards with no luck."

I wonder exactly what you were looking for. There are different ways to approach the project, and they vary with regard to what new connectors are utilized. And the connectors might also vary with regard to how easy or hard they are to find.

Keep in mind it's also possible to do the job with no new connectors at all. If you were on a desert island with no source of parts, you could do the whole job with a sharp rock, and some electrical tape. (When I say "whole job," I mean the wiring tasks. You would obviously need other simple tools to physically install the ECU and the O2 sensor.)

In the sharp-rock scenario, you are cutting factory wires, and taking an approach that's relatively hard to reverse. With the proper connectors, you can create an installation that's easily reversible without a trace, and you can completely avoid cutting any factory wires or altering any factory connectors.

"I just read the entire thread and am a bit confused as whether or not we need new connectors."

There are very specific reasons why the discussion is confusing. For example, I've pointed out that different people use different pin-numbering conventions.

It would help me to know your level of electrical literacy. Do you understand how to read this schematic (especially the referenced pin numbers)? It would be possible to do the job without this schematic, by following the instructions I posted above (about how to build a custom harness). But this schematic is helpful, and it will be easier for me to guide you if I know how well you grasp the schematic.

As far as whether or not we need new connectors, you have a choice. I have described a method that uses 4 new connectors. Wandering used 2. And as I mentioned, the job could also be done with zero.

"I always thought I had to run wires into the car, but it seems like I don't."

That claim (that it was necessary to run wires into the car) has been made, but I think Wandering and I have both discovered that the claim is wrong.

Swapping ECUs is the only work you have to do in the interior of the car.