Excessive lean condition--wb02 reads 15.0

EvilStig

New member
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*.
 

sefiroxx

New member
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.

Sent from my Pixel 5 using Tapatalk
 

EvilStig

New member
sefiroxx":1wnhm0yc said:
check vacuum leaks.

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

sefiroxx":1wnhm0yc said:
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":1wnhm0yc said:
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":1wnhm0yc said:
tps is off indicating less than normal air flow.

is there a way to test this?

sefiroxx":1wnhm0yc said:
pump is pushing too little fuel

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

sefiroxx":1wnhm0yc said:
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?
 
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.
 

RedCelicaTRD

Moderator
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!
 

EvilStig

New member
underscore":1mxk28ew said:
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.
 

EvilStig

New member
93celicaconv":osz9hcfy said:
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":osz9hcfy said:
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":osz9hcfy said:
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*.
 

EvilStig

New member
RedCelicaTRD":59dvb0m9 said:
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.
 

RedCelicaTRD

Moderator
EvilStig":395twfcr said:
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.
 
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
 

EvilStig

New member
93celicaconv":1ecnuczy said:
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.
 

EvilStig

New member
RedCelicaTRD":1e4n6kls said:
EvilStig":1e4n6kls said:
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....
 

alltracman78

Active member
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":317vxrup said:
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.
 

RedCelicaTRD

Moderator
alltracman78":15n8fz1p said:
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":15n8fz1p said:
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)
 

RedCelicaTRD

Moderator
EvilStig":191dyya1 said:
RedCelicaTRD":191dyya1 said:
EvilStig":191dyya1 said:
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.
 
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?
 

underscore

Well-known member
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.
 

RedCelicaTRD

Moderator
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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