Excessive lean condition--wb02 reads 15.0

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Excessive lean condition--wb02 reads 15.0

Postby EvilStig » Sun Jan 09, 2022 9:19 pm

My ECU keeps throwing a lean condition code ever since the smog shop tampered with things a couple years ago, and I installed a wbo2 to troubleshoot. It shows 15.0 at all running conditions, including under boost. I've so far replaced *all* of the hoses and pressure tested the system, no boost leaks... AFM appears clean and functional, and I've gone through 6x o2 sensors and 2x wbo2 gauges trying to isolate the issue... no luck.

Is there a good troubleshooting/diagnostic flowchart for this kind of fueling issue? I'm worried about damage to the engine even without boosting it as it is running *hot*.
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Re: Excessive lean condition--wb02 reads 15.0

Postby sefiroxx » Sun Jan 09, 2022 11:05 pm

Too much air or failing fuel system (pump or injectors).

Air
- check vacuum leaks. Old school: smoke machine or spray carburetor cleaner everywhere while yelling idling to see if idle jumps
- map sensor is sending low air pressure signal to ecu
- throttle is dirty
- tps is off indicating less than normal air flow.

Fuel
- pump is pushing too little fuel
- Fuel pressure regulator is open lowering fuel fuel pressure
- injector clogged or not opening.

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Re: Excessive lean condition--wb02 reads 15.0

Postby EvilStig » Mon Jan 10, 2022 12:29 am

sefiroxx wrote:check vacuum leaks.


no vacuum leaks. Intake holds pressure up to 30psi with smoke using boost leak tester.

sefiroxx wrote:map sensor is sending low air pressure signal to ecu


Does MAP sensor affect fueling? I thought all it did was fuel cutoff and boost gauge. I have an FCD installed between the sensor and ECU.

sefiroxx wrote:throttle is dirty


Didn't seem to be, but I'm going to pull it off and clean it a second time now while I have the charge cooler core off again.

sefiroxx wrote:tps is off indicating less than normal air flow.


is there a way to test this?

sefiroxx wrote:pump is pushing too little fuel


I don't think the pump is bad but I have another one on order anyway...

sefiroxx wrote:Fuel pressure regulator is open lowering fuel fuel pressure


Also have one of these on order but not sure how to test, or if it can be installed without pulling the engine...

[/quote]injector clogged or not opening.[/quote]

Seems unlikely since the car otherwise runs fine and there doesn't seem to be issues with any one cylinder?
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Re: Excessive lean condition--wb02 reads 15.0

Postby underscore » Mon Jan 10, 2022 5:44 am

Is the cap still on the AFM adjustment screw?
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Re: Excessive lean condition--wb02 reads 15.0

Postby 93celicaconv » Mon Jan 10, 2022 11:34 am

Do you have an otherwise stock ST185?

Are you still running the stock ECU?

How is your wb02 installed (maybe said differently, are you still using your original nb02 sensor and your wb02 sensor is a 2nd sensor)?

If running a stock ECU, are you getting any check engine lights / trouble codes?

I know on one of our two all-stock ST185's, one of the MAP sensors wasn't putting out a linear output signal relative to pressure changes (the others all are), and when using the particular MAP, the engine doesn't have the same torque at higher RPM's as when using a good "linear output" MAP sensor. So on a complete stock ST185, it sure feels like the MAP has some effect on fueling, even though I think the AFM has the primary influence.

Also, if your fuel quantities are being properly controlled, you should go towards rich when the engine needs to put out a high level of torque, and towards lean when coasting. If yours doesn't change at all - it almost seems like you are not getting a sensor input to the ECU - the air:fuel ratio should be changing. But if the ECU isn't getting an input, it should trigger a check engine light (at least a stock ECU). If you are running an aftermarket ECU - I don't know anything about those.
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Re: Excessive lean condition--wb02 reads 15.0

Postby RedCelicaTRD » Mon Jan 10, 2022 3:58 pm

There was some speculation back in the day that the map sensor has some control over timing but not fuel other then fuel cut.

If I was to start troubleshooting this I would look at the fuel pressure regulator. If you ordered a stock one it's just on the end of the fuel rail. No need to drop the engine. Best way to test is with a gauge. You can buy an adaptor that replaces the banjo bolt on the fuel filter. Then buy some fittings and hose and hook up the gauge and tape it to your windshield (or install an electric gauge). Drive around and see what happens. I had a fuel pump go bad and it was easy to diagnose with a ghetto gauge connection. Under boost the fuel pressure would drop down to about zero. For your situation it's probably not adjusting to changes in vacuum or boost and not adjusting fuel pressure. You might only have base pressure which is around 40psi? I cant remember.

Anyway, that is where I would start. No guarantees!
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Re: Excessive lean condition--wb02 reads 15.0

Postby EvilStig » Mon Jan 10, 2022 4:41 pm

underscore wrote:Is the cap still on the AFM adjustment screw?


No, the previous shop that did smog on it removed it and tampered with the idle adjuster. The AFM does not have a number stamped on it for the stock setting, or it has worn off, so it is impossible to return to stock. I have tried tweaking it but it does not seem to make much difference, and it should not have an affect at speeds above idle anyway since the air bypass opening is too small to make a difference when ingesting more than an idle amount of air.
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Re: Excessive lean condition--wb02 reads 15.0

Postby EvilStig » Mon Jan 10, 2022 4:55 pm

93celicaconv wrote:Do you have an otherwise stock ST185?

How is your wb02 installed (maybe said differently, are you still using your original nb02 sensor and your wb02 sensor is a 2nd sensor)?


intake, fueling and exhaust is stock other than the following:
cat-back resonator and muffler
st205 wta intercooler core
CT27 turbo mod
aftermarket BOV (in bypass mode, like stock)
greddy EBC, disabled (stock pressures)
FCD set to ~ 16PSI, so about 20% up from stock.
wbo2 AEM gauge in-line with nb output to the ECU to replace the stock nbo2


93celicaconv wrote:Are you still running the stock ECU?

If running a stock ECU, are you getting any check engine lights / trouble codes?


Yes. Only code is excessive lean condition. It usually comes on after ~ 200 miles of driving, or after any amount of boost following a reset.



93celicaconv wrote:I know on one of our two all-stock ST185's, one of the MAP sensors wasn't putting out a linear output signal relative to pressure changes (the others all are), and when using the particular MAP, the engine doesn't have the same torque at higher RPM's as when using a good "linear output" MAP sensor. So on a complete stock ST185, it sure feels like the MAP has some effect on fueling, even though I think the AFM has the primary influence.

Also, if your fuel quantities are being properly controlled, you should go towards rich when the engine needs to put out a high level of torque, and towards lean when coasting. If yours doesn't change at all - it almost seems like you are not getting a sensor input to the ECU - the air:fuel ratio should be changing. But if the ECU isn't getting an input, it should trigger a check engine light (at least a stock ECU). If you are running an aftermarket ECU - I don't know anything about those.


Do you think the FCD Then could be a problem child here? or perhaps a problem with the ECU itself?

I installed the FCD and CT27 before the problems began, but the engine was throwing the lean code already when I replaced the nbo2 with the wbo2, so I have doubts it is the o2 reading, despite the decidedly *odd* behaviour that the AFR is reading so steady across the map (and occasionally stopping reading at all... 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*.
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Re: Excessive lean condition--wb02 reads 15.0

Postby EvilStig » Mon Jan 10, 2022 4:57 pm

RedCelicaTRD wrote:There was some speculation back in the day that the map sensor has some control over timing but not fuel other then fuel cut.

If I was to start troubleshooting this I would look at the fuel pressure regulator. If you ordered a stock one it's just on the end of the fuel rail. No need to drop the engine. Best way to test is with a gauge. You can buy an adaptor that replaces the banjo bolt on the fuel filter. Then buy some fittings and hose and hook up the gauge and tape it to your windshield (or install an electric gauge). Drive around and see what happens. I had a fuel pump go bad and it was easy to diagnose with a ghetto gauge connection. Under boost the fuel pressure would drop down to about zero. For your situation it's probably not adjusting to changes in vacuum or boost and not adjusting fuel pressure. You might only have base pressure which is around 40psi? I cant remember.

Anyway, that is where I would start. No guarantees!



Thanks, I will definitely make this the next thing I try then...

Goddamn super headache getting to that fuel rail on these engines... I really wish Toyota hadn't cast the entire manifold as one piece like this.
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Re: Excessive lean condition--wb02 reads 15.0

Postby RedCelicaTRD » Mon Jan 10, 2022 5:44 pm

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.
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Re: Excessive lean condition--wb02 reads 15.0

Postby 93celicaconv » Mon Jan 10, 2022 6:41 pm

Just verifying your prior response, to ensure clear understanding:

- You are using a stock ST185 ECU, with no other ECU piggy-backed or involved
- You are using a wide-band oxygen sensor to feed both your AFR gauge and the ECU input
- There is no narrow-band oxygen sensor currently being used on your ST185
- You are only getting DTC 25 (Air:Fuel Ratio Lean Malfunction), but not getting DTC 21 (Oxygen sensor signal) or DTC 26 (Air:Fuel Ratio Rich Malfunction) ever
- Your ST185 was not built for California Emissions requirements
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Re: Excessive lean condition--wb02 reads 15.0

Postby EvilStig » Mon Jan 10, 2022 9:38 pm

93celicaconv wrote:Just verifying your prior response, to ensure clear understanding:

- You are using a stock ST185 ECU, with no other ECU piggy-backed or involved
- You are using a wide-band oxygen sensor to feed both your AFR gauge and the ECU input
- There is no narrow-band oxygen sensor currently being used on your ST185
- You are only getting DTC 25 (Air:Fuel Ratio Lean Malfunction), but not getting DTC 21 (Oxygen sensor signal) or DTC 26 (Air:Fuel Ratio Rich Malfunction) ever
- Your ST185 was not built for California Emissions requirements


All correct, except I am pretty sure is a 50 state model... I think all the USDM ones are?

It is a CA registered veh so it needs to keep most things stock or hidden, hence all the complicated nonsense with the stock cats and sensor bung etc.
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Re: Excessive lean condition--wb02 reads 15.0

Postby EvilStig » Mon Jan 10, 2022 9:40 pm

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....
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Re: Excessive lean condition--wb02 reads 15.0

Postby alltracman78 » Mon Jan 10, 2022 9:49 pm

Ca emissions is irrelevant here.
The only difference between that and Federal emissions (on these cars) is Ca emissions have a EGR temp sensor in the EGR valve while non Ca emissions have a resistor plugged in the harness instead of the temp sensor. ECU and harness are identical (IIRC there are 2 different part numbers for the harness but the only difference is one has the resistor in it).

EvilStig wrote:wbo2 AEM gauge in-line with nb output to the ECU to replace the stock nbo2


That's your problem right there. You can't just replace narrow band O2 with a wideband. They're two different signals. The stock ECU can't read the signal from a wideband. Just went over this in another thread a few weeks ago.
You might have another problem, but first you need to reinstall a just a narrow band sensor for the ECU.

Your wideband needs to be separate and only go to the wideband gauge.
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Re: Excessive lean condition--wb02 reads 15.0

Postby RedCelicaTRD » Mon Jan 10, 2022 11:46 pm

alltracman78 wrote:Ca emissions is irrelevant here.
The only difference between that and Federal emissions (on these cars) is Ca emissions have a EGR temp sensor in the EGR valve while non Ca emissions have a resistor plugged in the harness instead of the temp sensor. ECU and harness are identical (IIRC there are 2 different part numbers for the harness but the only difference is one has the resistor in it).

EvilStig wrote:wbo2 AEM gauge in-line with nb output to the ECU to replace the stock nbo2


That's your problem right there. You can't just replace narrow band O2 with a wideband. They're two different signals. The stock ECU can't read the signal from a wideband. Just went over this in another thread a few weeks ago.
You might have another problem, but first you need to reinstall a just a narrow band sensor for the ECU.

Your wideband needs to be separate and only go to the wideband gauge.


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)
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