Civic VX Lean Burn Questions

[GasSavers_James]

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.

[Wandering Albatross]

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!

[lca13]

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.

[Wandering Albatross]

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!

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.

[Wandering Albatross]

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?

[Wandering Albatross]

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.

[soletek]

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.

[Wandering Albatross]

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.

[Wandering Albatross]

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!

[soletek]

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.