Civic VX Lean Burn monitor and General Info
 

I've noticed lately a lot of interest in monitoring the Lean burn of the VX ECU. I did some searching (thanks to Krousdb) and found his post about which ECU pins to connect to with a DMM/DVM to monitor Lean Burn.



Enjoy!


Now for the info on the ECU pins to connect to and what you should be seeing:
Positive lead of the DMM/DVM to pin D14 (orange with blue stripe)
Negative lead to pin D16 (blue with green stripe wire)
https://www.gassavers.org/attachment....1&d=1168541520
Readings can be as low as -1.4V and as high as .8V
This is considered normal. In a good functioning LAF the peak-to-peak voltage difference should exceed 1 volt. I.E. if you get a reading of -1.3V (rich) and .6V (lean) the voltage range is 1.9V which is acceptable as a proper functioning LAF.

Checking Reference Voltage:
Positive Lead on D16 | Negative Lead on Chassis Ground
https://www.gassavers.org/attachment....1&d=1168541829

These wires are located on the far right connector once the ecu is orientated like the ECU picture below.

Courtesy of FF-Sqaud.com:

https://www.ff-squad.com/tech/wiring/wiring.92-95.jpg


What it is:
D14 is the IP+ (positive pump cell) signal of the LAF and D16 is the IP- (negative pump cell), VS- signal of the LAF (VS- is the Reference Voltage that the LAF uses, the voltage is 450mV, measured from the Cell Voltage Input D8) (Ip- is the "virtual ground" the LAF uses...so basically the LAF reference signal is at 450mV (2.7V measured from Chassis Ground) unlike a typical earth ground which resides at less than 10mV). This has all been checked out by me in the Helms Manual (the FSM for Honda).

Whew! That was some reading! If you didn't get it the first read, that's fine. Just go back and read it again until it does make sense. There is much more that I could type and quote from the training manual, but I'm at work while typing this and I have to get some things done here. ;)

PCV info for CX/VX model:
I just checked on my Honda E-catalog (the same software the dealer uses) and got different numbers for the VX/CX model as compared to the rest of the models.

VX/CX = PCV 17130-P07-A02 (shown to be used on all CX/VX model civics 92-95) The rest = 171300-PM6-003 (all models except CX/VX)

The reason for posting this info is because the VX/CX PCV valve is not like a normal PCV valve. It's basically a 90 degree elbow with no innards. This allows the crankcase to be under low pressure most all of the time allowing for better FE.

DIY on making an aftermarket PCV into an OEM VX PCV

Usually Honda has the parts grouped by ECU ie VX=P07 and the correct corresponding parts have that in the middle of the part number. So it seems that VX and CX share the same PCV valve.

Displays that can be used with the VX LAF:

It wouldn't be too hard to rig up a simple voltage comparator circuit to light up an LED when the signal from the O2 goes higher than the reference signal. hmm, but for me, it's just easier to hook up a DVM. Tech Edge has a display that can read a LAF as well, in fact the controller kit they used to sell has a heater controller circuit as well. And the cool part...the display shows A/F ratio or voltage depending on how you set it up during assembly.

Wide band display HERE

Tech edge site HERE

This company actually uses the VX L1H1 sensor in it's first version of DIY kit.

Spark plugs and wires:

The VX uses NGK V-Power Spark Plugs No. ZFR4F-11

Spark plug wires from the dealer are best and worth the money. If you do buy spark plug wires from an auto store, buy them for an Si model of the same year. This ensures that you get the proper fitting plug wires since some auto stores have the wrong part number in their system for the VX spark plug wires.

Tire Size:

The original tire size of the VX was 165/70/R13

This tire size is getting a bit harder to find.
Use this table HERE to find a tire size near the original stock size. If you don't have the stock rims, you can see similar sizes on larger rims by clicking "show" on your rim size below the table.

VX Specific Aero Parts:
There are two specific Aero Parts for the VX. They are the front lip spoiler and a rear cover for the void between the driver's rear bumper and wheel well.

https://www.hondaautomotiveparts.com/...13sr30_g12.gif
74663-SR3-H00 Cover RR. Lower 92-95 VX specific part only. $38.92 before shipping at Majestic Honda. It's number 14 in the picture above. Direct Link Here

Here are pics of my VX with rear panel from the factory:
https://www.imagestation.com/picture/...d/ea688587.jpg
https://www.imagestation.com/picture/...f/ea6884d2.jpg
Taken from the drivers side rear of the car.

https://www.hondaautomotiveparts.com/...13sr30_g01.gif
Number 4 in this picture is the front lip spoiler. 71110-SR3-000 Spoiler, FR. AIR. Going for $70.88 on Majestic Honda. Direct Link Here The front lip isn't so much VX specific as it was a dealer option on all two door and hatch model civics.

Rust repair panels for the rear quarter panels:
212-92-51-L
212-92-51-R
Rust Repair Site

Click on "order by part number" button in the upper left of the page and enter one part number per line. The current price is $32.35 per panel, but well worth it. Shipping is pretty reasonable as well.


Disclaimer!

I know it's a lot of info all in one post, but it's nice to have it all in one spot for search reasons. And a big Thank You to DaX and Krousdb for helping me!

And as always...Your Mileage May Vary! :D

bravo... :)

https://autospeed.drive.com.au/cms/A_3032/article.html

has air/fuel gauges, altho non of them read 22:1 ratios, but they should still tell you when you hit that lean spot.

Thanks for the link, Ryland.

If you've got the dough, get a PLX M-series lambda meter...I don't know exactly how much they are, but they're nice, and they can read all the way up there in those high AFR values. www.plxdevices.com

Not bad, the meter itself is $79 and will read 0-5V linear, which means that 2.5V is stoich. I'm not sure if the L1H1 is set to output 2.5V stoich. I'll check on this and get back to this post.

I haven't had a whole lot of luck finding a graph of the actual output in Volts of the L1H1.

But I did update some more info in the original post. Tire sizes and some other stuff.

TomO: Where did you find the price of $75? It looked to me like their sensor is the Bosch unit, which was running a couple of hundred bucks, when I was looking at this six months ago.

Have you been unable to find a voltage/fuel ratio curve for the sensor in the VX. If you can't find one, I think I can find something out for you, although it may take me a couple of day's. Presuming your car is a non-CA VX, you should be able to get all of the information that is available through that monitor, by just using a voltmeter and the sensor/controller which are already built into the car.

I have found two formulas for the NTK L1H1:

V = (AFR - 9) / 2 ~> https://wbo2.com/2a0/
V = (AFR - 10) / 2 ~> https://www.ztechz.net/id12.html

Not sure exactly which one is right.

HERE is the page that has just the display available for $79. Sorry, I should have clarified that price was just for the gauge. And now looking at it again, it says it must be connected to their sensor unit for proper function. I bet there could be ways around that though.

I have been trying to find a Raw Voltage output table of the L1H1. As in what voltage range does it operate in. I know everyone says that a Wideband O2 operates from 0-5Volts but all the graphs I've seen over my last three days of searching are of the output from the controllers of the L1H1. Like the Diy Ozzie one... that is their adjusted output graph to their display.

This is what I understand from what I've gathered on the workings of the L1H1:

Vref = 450mV = .45V (This is the reference voltage the controller uses to actually read if the air is rich or lean)

Now, what I get from all that is...the WB controller reads the Ip (pump current) and then translates it into a Vout (voltage reading). So basically it's all voltages between 0-1V up to the controller (albeit in the Ozzie unit or the VX ECU) and then the Ozzie unit spits out a voltage based on their circuitry for their display to read and the VX ECU looks up it's fueling tables based on the pump current it is reading from the L1H1.

So up until this time, either I'm way over-analyzing this OR I could just simply go out to my VX and hook up my DVM to the Ip and the sensor ground to get a full reading of the voltage range the sensor spits out.

I wish it wasn't so cold outside and I had a spare set of DVM leads to solder in to my ECU so I could see all this for myself.

I'm getting so involved with this because I have a couple of the original Ozzie units (the controller and the display) that I started to assemble. I would like to see if the display could be hooked directly to the output of the L1H1 since the VX ECU will be controlling the sensor. Now you can see why I want a RAW data output graph of the L1H1. I know the Ozzie display is calibrated to read 2.5V as stoich and I want to see what the output of the L1H1 itself is.

Sorry, this is getting long-winded now, and I'm hungry. I'm going out to get some lunch and try to not rack my brain on this one.

Using that formula:

to get V=2.5 (theoretical stoich given a range of 0-5V)
then the formula should read

V = (AFR - 9.7) / 2
Given the AFR = 14.7
then V = 2.5V

Ok seriously, I'm going to lunch now. :D

Well I can't shrink it small enough to attach here, but I can email you a .pdf file from the OBD Honda training manual that has the section on the LAF sensor (wideband). Just PM me your email address.

Ok. I have looked at all of these page's and every time I get to where I think I understand it entirely, I read something else and it doesn't seem to make sense with what I've read, so my brain starts stripping gears and pouring out smoke.

From what I understand the Vref is a voltage which is essentially defined by the controller and consequently, different controllers use a different voltage, which is part of the confusion. Additionally, it does sound to me like the various unit's do a translation or interpretation of the output of the O2 sensor, so that it gives a more easily understandable output for end users to interpret, aka 0-5 volt's. Also, it sounds like the sensors are not all exactly the same, so some of the controllers also make an allowance for calibration of the tool, to make it so that the output's are consistent.

My expectation is that their is some variation in O2 sensors, in general, but with a 1-4 wire sensor, it isn't particularly critical, because what the ecu is really looking for is a sharp transition from one side of the output, to the other, and then the ecu just keeps constantly adjusting the injection rate, up and down, so that the air-fuel ratio is constantly passing through stoich, in a ongoing, up and down fashion.

On the 5 wire sensor's, I think their operation is a little more complicated, but that the ecu is looking at the O2 output voltage, in comparison to the Vref voltage. Consequently, I think the voltage off of the O2 sensor, utilizing Vref as the reference voltage, has a 0 point which is stoich. When the engine/sensor is warmed up, the ecu moves the air-fuel mixture, up and down, similar to the fashion a standard ecu does with a standard O2 sensor. My expectation is that it then utilizes some offset value, as a change amount, for the voltage it is looking for when it goes into lean burn.

Here is what I do know. I have a 1989 honda Civic Wagovan, 1.5L DPFI. I replaced the 1 wire O2 sensor with a 4 wire O2 sensor. I also wired the output of the 4 wire sensor and ground wire, into my car, temporarily, so I can monitor the output voltage. What I discovered was that with the 4 wire unit, it warms up and becomes operational in about 2 blocks, allowing the ecu to go into closed loop operation, substantially faster than with the 1 wire unit. In closed loop, the voltage oscilates between about 0.7v and 0.4v, in a cycle which is about 1-2 seconds long. If I let the throttle fully off, then the voltage drops to about 0.25v and will remain their until the engine rpm drops to about 1200 rpm. Under acceleration, the ecu will stay in closed loop operation, until I get down around 5 in of vacume, at which point the ecu goes into open loop and uses the lookup tables in the ecu. This is observable from the O2 sensor voltage, which goes up to about 0.8 or 0.85, and will stay relatively constant until the vacume get's back about about 5 inch's.

I hope this makes some sense and will help you some.

On the Aussie unit's, which one's do you have, how completed are they and do you know which sensor they are appropriate for? It looked to me like their different units were optimized for different sensor's.

I hear you there, that completely describes my brain at the moment. :eek:

You're dead spot on with that thought! :thumbup:

Exactly! The ECU is shooting for stoich (usually .45V-.5V) but it's impossible for the ECU to obtain this since the entire range (also read resolution) is only 0-1V. Therefor the ECU constantly adjusts injector pulse width up and down in an attempt to maintain a .5V signal from the O2

You are correct again! The Vref (reference voltage) is the "stoich" value the ECU is attempting to reach. But also this Vref acts as a virtual or "floating" ground for the Nernst Cell (the part of the O2 responsible for generating the Vs signal to the ECU). So this means that when all air is consumed by fuel (stoich) the signal is equal to the Vref signal. So virtually the signal is 0 when measured from Vref to Ip+. In reality the signal is .45V measured from the sensor ground to Ip+ according to my findings so far on the L1H1.

picture courtesy of Tech Edge:
https://techedge.com.au/vehicle/wbo2/info/wbcell.gif

Not sure on the offset value, until I do more reading. I'd love to just download the P07 bin file and look at the code and tables from PGMFI.org but I have a 16 month old daughter and a wife that won't let me. ;)
The reason Wideband O2 sensors are better at maintaining a stoich value is do to the range (read resolution) of the sensor. Having a table for a 1-4 wire O2 looks like a 0-1 for a Y-axis and the A/F ratio for the X-axis:
https://www.zeitronix.com/questions/O2transfer.gif
Which is horrible for a table to read.

But the Wideband has a much larger resolution and therefor has a larger lookup table in the ECU for accurately controlling the injectors.

It all makes perfect sense to me. And thanks for sharing that info.

I have the very first one that they came out with HERE.
They are designed for the L1H1 (the sensor that is stock on the non-CA emissions VX)
I have completed the display portion of one of them and was working on the controller board. I might only have one left as I originally purchase 3 units to assemble and use for tuning 89-90 Turbo Grand Prixs.


So for now, I'll wait to see what Dax sends me and I'll do some reading and get back to this post. I'm thinking I have seen the proper info, but it just might not be clicking in my brain yet. I'll have to go over my schematics of my WBO2 kit and trace the Ip signal through the controller board and see if and how it is modified to get my answer on using the display directly with the VX ECU. It would be awesome if we could because then all the VX owners here could have a neato display to watch their A/F ratios as they drive.

You dont need spare lead really. I just got some wire and male female butt connectors. I took my DVM lead to match up its end with the male butt connector. I ran the wires put the male connector on each one and marked the wires. I can just plug them in when ever I want to see it. When I dont I take a female connector wrapped in tape and put on on each male and stuff the back up under the dash.

Good luck and thanks for the input so far.

I can't thank you enough DAx for getting me that manual!

I've already learned enough to get a great sense of the voltages I want to see for hooking up my Aussie WB display. I'm going to finish reading the chapter on the LAF and then post a version that we can all understand.

What I did on my sensor, was I added a little stub, where I wired the sensor into the connector. I just put a small wire nut over the stub end when I'm not using it and when I want to use it, I wire a cable in, using the wire nut. It seems to work Ok.

Wife, 16 month old, I'm impressed your able to even get to the web site.

Welcome!

Lol, yeah, I usually get some guff about being on teh computer once I'm home from work.

Thanks man! oh, and Number Munchers ROCKS!!! :cool:

Ok, so here's the breakdown of the voltage tests for the L1H1:
Measuring Vref, (pin 8 on the L1H1 connector, D16 on the ECU) to chassis ground (Pin 2 on the L1H1) yields a reading of 2.7Volts. This is the stoich value Honda has chosen to shoot for.

Measuring Pump Cell voltage (the signal the ECU uses to read A/F ratio) measure between D14 (+ lead) and D16 (- lead)
Rich ~ -1V
Lean ~ +.42V and up


Now, what this all means for me and others that are interested:
The operating Voltage range of the L1H1 (allowed by the ECU) is ~1.4 to 3.1V
I now know the output graph of the L1H1. Ironically it's the same as the output of the DIY ozzie WB controller board (ver 1.0). That means that I can take the display from that kit and hook it up to the ECU and have an actual readout of the A/F ratio and not just the voltage reading. I just need to recalibrate the unit, which is pretty easy.

So now, I'm going to make up some nice charts and graphs along with wire colors and pinouts, and possible simplify the theory of the LAF. But that means it has to wait until tomorrow morning while I'm at work. So stay tuned for more exciting updates as they occur. :cool:

Oh I will. Now if I only understood this stuff......

:thumbup: :eek: I just added more pictures and information that I believe will be extremely helpful to current/future VX owners, or for anyone running Versions 1.0 thru 1.5 of the DIY WB O2 kits from Tech Edge. It's a lot of reading but it's worth it. Just PM me or post here any questions you might have since this has kind of turned into the end-all VX information thread.

would something like this work to monitor the LAF? its nice, small, and backlit. it displays +/- polarity as well.

https://cgi.ebay.com/20VDC-BLUE-LED-A...QQcmdZViewItem

It looks like it would work as a monitor.

There are two ways of monitoring the LAF:
Positive lead of the DMM/DVM to pin D14 (orange with blue stripe)
Negative lead to pin D16 (blue with green stripe wire)
for a reading of -1.xVolts to +.XVolts. + being in lean burn mode.

OR

Positive lead to D14
Negative lead to chassis ground or D22 (sensor ground)
for a reading from +0.xV to +3.1V (lean burn is when readings are above 2.7V)

Added more info about Aero parts today.

Are the ECU connector pins the same on the later HX? Are the O2 sensors the same (L1H1)? Thanks

The HX uses a different O2, the cheaper L2H2.

And the pinouts of the ECU on the HX are different as it is an OBD2 vehicle.

If you're just trying to monitor the AFR with a wideband, see the link below. The LC-1 with the Bosch sensor is $199. It allows both an analog output (monitor with DMM) or a serial output so you could datalog your AFR's.

https://www.diyautotune.com/catalog/w...d327536136be3b

anyone know where I can get a cheap L2H2? Would a L1H1 work?--Just wondering. Does the Lean Burn on the HX function with similar voltage outputs? Thanks for everything.

Your best bet would be to check Ebay for the L2H2 or Oxygen Sensor Warehouse

L1H1 is more expensive than the L2H2 plus it's best to stick with what your ECU is expecting for readings. They have slightly different output curves if memory serves me correctly.

UPDATE!

I have added info for rust repair panels.

I have 2 VXs for 2 years now and love them. Would like to get a LED indicator that shows when in lean-burn mode if possible. Does anyone make one or have instructions to solder something together to indicate to the driver that engine is operating in lean burn mode? Even if I can splice a wire that is open/closed circuit I can install a relay and a light to turn on when its state goes hi/low?

Thanks for any help or experience doing this already.

Do a search you need tap into the vtec solenoid. someone has done it either on here or on ecomodder. I think it might have been lean burn enthouiest saying he did it.

so far, no results
 

Tried your pins suggested here, d14/d16 and I git some voltage sometimes when the car is cold, but right away it drops to near zero. Fluctuating in the .005 to .0005 kind of range. One of those pins to chasis ground gives me the 2.7 always (reference v?).

This is on my old O2 sensor (says L2H2 on it) and on a new one from o2sensor.net

Those pins were not the colors you described, and I have not had time yet to go back in and test any possibilities. Just wondering if you have any suggestions first?

my /problem/ is I get a stumbling hesitation at low throttle levels when I'm trying to maintain a gentile cruising speed. If I unplug the O2 sensor this goes away. Replacing the o2 sensor did nothing. Any suggestions what else would cause this? I also do not notice lean burn kicking in on the mpgUino display.

Thanks for any advice!!!

i have this same problem with my lean burn and from talking to a shop today a guy had his vx in thier for the same problem, they said every time it stumbled is when lean burn was kicking in, confrimed from a wideband they had hooked up while testing it the afr's would be very high on low rpm throttle tip etc.. the same thing i complained to them my car was doing to, so from what it sounds like then that this is the norm for any lean burn motor