Civic VX Lean Burn monitor

[GasSavers_TomO]

Originally Posted by DaX

I have found two formulas for the NTK L1H1:

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

Not sure exactly which one is right.

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.

[GasSavers_DaX]

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.

[Gary Palmer]

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.

[GasSavers_TomO]

Originally Posted by Gary Palmer

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.

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

Originally Posted by Gary Palmer

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.

You're dead spot on with that thought!

Originally Posted by Gary Palmer

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.

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

Originally Posted by Gary Palmer

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.

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:

Originally Posted by Gary Palmer

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.

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:

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.

Originally Posted by Gary Palmer

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 vacuum, 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 vacuum gets back about about 5 inch's.

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

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

Originally Posted by Gary Palmer

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 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.

[GasSavers_Jack]

Originally Posted by TomO

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.

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.

[GasSavers_TomO]

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.

[Gary Palmer]

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.

[GasSavers_DaX]

Originally Posted by TomO

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.

Welcome!

[GasSavers_TomO]

Originally Posted by Gary Palmer

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

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

Originally Posted by DaX

Welcome!

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

[GasSavers_TomO]

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.