Excessive lean condition--wb02 reads 15.0

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Re: Excessive lean condition--wb02 reads 15.0

Postby RedCelicaTRD » Mon Jan 10, 2022 11:52 pm

EvilStig wrote:
RedCelicaTRD wrote:
EvilStig wrote: but I suspect that may be from the sensor exceeding the max safe exhaust gas temp---something the lean condition is likely causing, judging by the fact that my 2000 degree F ceramic header paint is burning off the heat shielding near the o2 bung.)

Do you think it is safe to drive *at all* in this condition? I feel worried that I may be harming the engine every time I start it up to test another change since I need to drive it x miles for the ECU to re-learn... even though I am careful not to get on boost *at all*.


Have you checked the ignition timing? Severely retarded timing will make EGTs go through the roof. Since combustion happens later in the cycle due to the improper timing you don't give the engine the opportunity to absorb some of heat and for the heat to provide expansion. The exhaust valve will crack open during this process and the hot exhaust will escape out into the manifold. Cylinder pressure also goes up and combustion efficiency is impacted. Retarded timing also causes the A/F gauge to read lean due to this change in combustion efficiency. Increasing timing causes a reduction in free oxygen which causes the gauge to read rich, decreasing timing causes an increase in free oxygen causing the gauge to read lean. Since the AFR gauge responds to changes in free oxygen AFR gauges can easily lead you down a wrong path due to the way they operate and there are a few "got-ya" situations that can really mess with your thought process. It's important to remember that the incoming A/F mixture might be correct, but the combustion condition in the cylinder has changed. Since the A/F sensor only looks for one type of gas - free oxygen - we really only have one data point on what is happening in the cylinder. Since we have stepped outside the ideal operating conditions for the sensor it will lead us astray.


What would be the best way to check for this?

I ask because this engine is notoriously difficult to see or access any part of it for diagnostics while it's assembled in the car....


You will need a timing light and a paperclip to verify base timing. You use the paperclip on certain spots in the diagnostic port to put the ECU into "test" mode which puts the timing to a fixed value and does not adjust the timing like it normally would. Then the timing light pickup gets put over the #1 plug wire. Then you point the timing light at the crank pulley and you should see a little white line on the pulley that lines up with the timing tab on the timing cover. Sometimes they are dirty and you need to clean them and add new white paint. Stock is 10* BTDC. Adjustments are made by rotating the distributor after you loosen the bolts that secure it to the head. There are a few how-tos on the internet for testing Toyota timing.

If you grab the distributor can you rotate it? It would rotate towards the front and rear of the car. Could be the bolts are loose and the distributor has moved.
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Re: Excessive lean condition--wb02 reads 15.0

Postby sefiroxx » Tue Jan 11, 2022 4:05 am

Be careful running hot as you could melt the cat.

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Re: Excessive lean condition--wb02 reads 15.0

Postby 93celicaconv » Tue Jan 11, 2022 12:40 pm

One would need to read the narrowband output of the AEM gauge. A wideband output is a linear signal depending upon the air:fuel ration being measured. The narrowband output is a cyclic 0-1V output where the ECU determines the amount of time that wave signal is above 0.5V vs. below. If the time is equal, the engine is runing at 14.7 air:fuel. Does that AEM gauge provide a wave signal with that 0-1V output, with about 1 or slighly more cylces per second?
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Re: Excessive lean condition--wb02 reads 15.0

Postby underscore » Tue Jan 11, 2022 3:57 pm

Maybe a silly question, but does that model of wideband have any sort of user configuration or a calibration mode or anything? Does it fluctuate from 15.0 at all? I don't know what the range on it is but when I'd let off and coast in gear (so zero fuel going in) my Innovate would go up to its max range of 20 or 22 or something like that.
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Re: Excessive lean condition--wb02 reads 15.0

Postby RedCelicaTRD » Tue Jan 11, 2022 9:30 pm

If I remember right 15.0 is the highest the display goes but the sensor can output ranges higher then that. I can’t remember 100%. I do know the Innovative display has a wider range but the overall sensor range is the same between the two. If the AEM is past it’s display value I’m trying to remember if it shows “- -“. There is a free-air calibration that you can do; would have to look at a manual for the process.
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Re: Excessive lean condition--wb02 reads 15.0

Postby 93celicaconv » Tue Jan 11, 2022 10:04 pm

What model is your AEM gauge?
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Re: Excessive lean condition--wb02 reads 15.0

Postby grip-addict » Wed Jan 12, 2022 4:19 pm

+1 for checking timing. Being over 15 across the board doesn't make sense. Nor would it be safe, if that was indeed what was happening.

Echoing prev comments (just because they are correct and you really should do this), make sure your timing is correct. Check and make sure that the base is fine and correct if need be. Then if that's on, check the cam notch marks as compared to the crank pulley and make sure they are all lined up.
If your timing is too retarded, it will cause the fuel to continue to burn on the way out of the motor and will cause your o2 sensor to record lean values.

Also possible is that your fuel pressure is wonky and the factory ecu is injecting fuel based on how much pressure it thinks it has vs what it does. The only way for you to test that is to hook up a gauge and take it on a drive though.
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Re: Excessive lean condition--wb02 reads 15.0

Postby alltracman78 » Wed Jan 12, 2022 5:21 pm

RedCelicaTRD wrote:
In his previous post he mentions that he is using an AEM Wideband gauge. The AEM gauge has a narrowband (0-1V) output to go back to the stock ECU along with the Wideband output that in this scenario would be unused. But since we should aways double check here is how I assume it is hooked up:

(WB Sensor)----(AEM Gauge)----(Stock ECU)


No kidding. I didn't know that.
That's pretty handy...

To me this still seems like something with the O2 signal. Either something is hooked up wrong or the internal converter is faulty. Or there's a massive exhaust leak at the sensor. I can't realistically see anything else causing the engine to run this lean at idle and still be able to make it to higher RPMs while driving.
I would get a new narrow band O2 and check with that (You can just get a universal single wire O2 sensor to check the signal. That eliminates all the wiring as well. Just to be sure. Install in the down pipe and hook the single wire up to a cheap A:F gauge or a analog volt meter. You don't even need to connect it to the car wiring. Make sure it's warmed up first. You'll know when it's warm because you'll get a signal.)

Or you can rule out the free stuff first, like checking timing and whatever else won't cost you any money. And then move on to stuff you have to buy parts to do. :shrug:
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Re: Excessive lean condition--wb02 reads 15.0

Postby alltracman78 » Wed Jan 12, 2022 5:58 pm

93celicaconv wrote:One would need to read the narrowband output of the AEM gauge. A wideband output is a linear signal depending upon the air:fuel ration being measured. The narrowband output is a cyclic 0-1V output where the ECU determines the amount of time that wave signal is above 0.5V vs. below. If the time is equal, the engine is runing at 14.7 air:fuel. Does that AEM gauge provide a wave signal with that 0-1V output, with about 1 or slighly more cylces per second?


I promise I'm not trying to pick on you man, just trying to make sure correct info gets out there. :)

Either O2 (narrow or wideband) goes off the O2 amount in the exhaust. The signal only fluctuates if the O2 level fluctuates. Just like if you quickly step on and off the gas pedal your TPS signal will quickly cycle. The nature of the narrowband O2 isn't to automatically give a cyclic or a wave signal, it only responds to what the ECU is doing and only gives a wave signal if the ECU is quickly adding and taking away fuel. Look at when the engine is in open loop, or deceleration, or when a narrowband is used to monitor a catalytic converter. There's no wave or cyclic signal in any of those cases (certain exceptions with newer catalytic monitoring, but that's irrelevant here).
The wave signal is directly in response to (and only happens when) the ECU is in closed loop and is constantly adjusting fuel trim.

The wideband signal is a less "excitable" version of the narrowband signal. It also cycles during closed loop. It's just not as dramatic as the narrowband because it reads a much larger range than the narrowband does.

*Here, this is a good article on the O2 sensor. I ran over it quick and it looks like it's just for the narrowband one FYI. Lots of nerdy info though. :P
https://www.linkedin.com/pulse/how-test ... concepcion
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Re: Excessive lean condition--wb02 reads 15.0

Postby 93celicaconv » Wed Jan 12, 2022 7:18 pm

Your not picking on me. I think we are both trying to help EvilStig out with his issue.

The subject is very hard to properly explain and understand using text only. Trying to explain causes confusion most often. I get that.

The attached file (Narrowband O2 Sensor Output) does a nice job explaining how a narrowband O2 sensor works. Yes, you are absolutely right, both the wideband and the narrowband O2 sensor outputs only have output changes if the measured O2 level changes - agreed. The narrowband O2 sensor output can really only measure over a small range of measured O2 (air:fuel ratio range of about 14:1 to 15:1). As such, in a working system, the typical narrowband O2 sensor's output over time is that of the top chart in the attached file (Narrowband O2 Sensor Output Over Time), and if not working properly, would be like either of the bottom two charts in the same file. In a properly working system, the BGB on the USDM ST185 says one should see voltage fluctuations 8 times or more in 10 seconds (like illustrated in the top chart). This is where I used the reference of fluctuation, because that is all a narrowband system can do, is frequently fluctuate.

The wideband O2 sensor, in contrast, can measure over a much larger range of O2 (air:fuel ratio range of about 0.8:1 to 2.2:1) as per the last attached file (Wideband vs Narrowband O2 Sensor Outputs). It's output signal is also different - it is a current signal generally in the 0 to 2.5 mA range.

So this will clearly explain why a wideband O2 sensor cannot be used directly on a narrowband ECU system, or visa-versa.

There are some controllers out there that can take a wideband O2 sensor current output, and send out a simulated voltage output in the same range as a narrowband O2 sensor, to provide this feedback to a narrowband ECU. I was asking EvilStig what model AEM gauge he is using to look up the specs to see if and how it creates the simulated voltage output to the narrowband ECU. I just wanted to make sure the AEM gauge is capable of generating a narrowband ECU friendly voltage input. The AEM wideband gauge should be able to display AFR's above and below 15:1, so with it displaying a fixed value at all engine RPM's and loads, I'm getting a feel the narrowband ECU is operating in an open loop all the time. It may be possible the AEM gauge is requiring a specific wideband O2 sensor (like a Bosch 4.9LSU) if this gauge is using cable with a resistor in the cable calibrated for a specific wideband O2 sensor. If this is the case, a free-air calibration may be required for a wideband O2 sensor if not the one the gauge was made for. Or the wideband O2 sensor the AEM gauge was made to utilize may have to be obtained. Just don't know, so was asking many questions.
Attachments
Narrowband O2 Sensor Output.jpg
Narrowband O2 Sensor Output Over Time.jpg
Wideband vs Narrowband O2 Sensor Outputs.jpg
Last edited by 93celicaconv on Wed Jan 12, 2022 7:37 pm, edited 1 time in total.
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Re: Excessive lean condition--wb02 reads 15.0

Postby RedCelicaTRD » Wed Jan 12, 2022 7:21 pm

I think things are getting a bit confusing in here. I don’t have the (vehicle) issue. I’m going to hold off on commenting until EvilStig gets a chance to do some testing.
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Re: Excessive lean condition--wb02 reads 15.0

Postby 93celicaconv » Wed Jan 12, 2022 7:39 pm

RedCelicaTRD wrote:I think things are getting a bit confusing in here. I don’t have the (vehicle) issue. I’m going to hold off on commenting until EvilStig gets a chance to do some testing.

My mistake. Should had said EvilStig. I've corrected that error now in my previous post. Thanks for finding my error.
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Re: Excessive lean condition--wb02 reads 15.0

Postby RedCelicaTRD » Sun Jan 23, 2022 4:49 am

I stand corrected! The AEM wideband does not provide a 0-1v output. Other brands like PLX do, but AEM does not.
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Re: Excessive lean condition--wb02 reads 15.0

Postby 93celicaconv » Sun Jan 23, 2022 1:56 pm

RedCelicaTRD wrote:I stand corrected! The AEM wideband does not provide a 0-1v output. Other brands like PLX do, but AEM does not.

In all of EvilStig's posts, I was trying to get to know the model/part number of his AEM wideband controller, but so far, we don't have that information yet. Maybe AEM doesn't have model/part numbers on their controllers? When I looked up information on AEM, I also saw that none of them had a simulated narrow band 0-1VDC output for narrow band ECU's, but that is what AEM is selling today, not necessarily what EvilStig may have (he may have an older model that, at the time, was made with that simulated narrow band 0-1VDC output for older ECU fueling control). Was just trying to get all the information that we could to try to provide some help.
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