strange fuel trim behaviour

[martin_oz]

Hi like so many of these posts I am another beginner. I have completed a rebuild on my L76 which has included DOD delete the new cam is a Lunati Duration @.050" 212/218 0.531 lift 113 LSA. my goal is to get the car running well enough to safely bed in the new rings and bearings before getting it Dyno tuned. So far I have turned off the DOD and increased the idle sped by 75RPM.
I initially had bank 1 O2 sensor codes and P071/P074 I switched sides with them tightened the inlet a little and the both rears started working but front bank1 reads low and lean bank 1 code , I discovered a a broken ground and corrected it, o2 sensor started working, I reset LTFT and the voltage picked up all looked ok.
I started it the next day bank 1 LTFT and STFT around 25% bank 1 O2 sensor output between 20 and 48 mv Bank 2 sensor working fine. I reset LTFT VCM scanner and O2 sensor rights itself and the LTFT appears to work properly.
My next step is to replace the Injector o-ring seals in case they leak when cold. I am open to suggestions on what else could be causing this problem. I have tried to upload my most recent log file.




22-05-02 12-10-44.hpl

[blindsquirrel]

Looks like B1S1 is shorted to ground at the beginning of the log, then un-shorts after a while when it heats up, which usually points to an internal problem in the sensor and not wiring problems.

[martin_oz]

Looks like B1S1 is shorted to ground at the beginning of the log, then un-shorts after a while when it heats up, which usually points to an internal problem in the sensor and not wiring problems.

Thanks for your reply It’s possible I need to replace them but I don’t think it’s going to be that easy, there was a ground issue which I fixed. The sensor starts working when I reset the LTFT, it works ok after that. I would have replaced it already but when I swapped the B1 and B2 sensors it made no difference the issue stays on bank 1.

[blindsquirrel]

Both heater circuits functioning? Does the scanner show the default bias voltage of ~450mV with both sensors unplugged?

[martin_oz]

Both heater circuits functioning? Does the scanner show the default bias voltage of ~450mV with both sensors unplugged?

I had heater faults on the bank 1 rear sensor but it went away when I swapped them, I assume it had a connection issue.
I will need to unplug them to try that, it might take a day or 2 to get time. Can I assume if the default isn?t ~450mv it might be in the wiring?

[Shrek]

Hi like so many of these posts I am another beginner. I have completed a rebuild on my L76 which has included DOD delete the new cam is a Lunati Duration @.050" 212/218 0.531 lift 113 LSA. my goal is to get the car running well enough to safely bed in the new rings and bearings before getting it Dyno tuned. So far I have turned off the DOD and increased the idle sped by 75RPM.
I initially had bank 1 O2 sensor codes and P071/P074 I switched sides with them tightened the inlet a little and the both rears started working but front bank1 reads low and lean bank 1 code , I discovered a a broken ground and corrected it, o2 sensor started working, I reset LTFT and the voltage picked up all looked ok.
I started it the next day bank 1 LTFT and STFT around 25% bank 1 O2 sensor output between 20 and 48 mv Bank 2 sensor working fine. I reset LTFT VCM scanner and O2 sensor rights itself and the LTFT appears to work properly.
My next step is to replace the Injector o-ring seals in case they leak when cold. I am open to suggestions on what else could be causing this problem. I have tried to upload my most recent log file.

You failed to post your tune - which makes it quite difficult to provide a more specific answer.

Also, the DTCs that you listed are missing a digit - these are made up of a letter, and a 4 digit number.

Given that you mentioned the fuel trims hitting 25% - I will assume that the DTCs are actually P0171 and P0174 - indicating that both banks are lean.

Often when these DTCs are set, the ECM will default to running in Open Loop - and ignore the Oxygen Sensors, until the DTCs have been cleared.

In your case, running in Open Loop is likely not safe - as it appears that your overall calibration is very lean for whatever reason.

[martin_oz]

You failed to post your tune - which makes it quite difficult to provide a more specific answer.

Also, the DTCs that you listed are missing a digit - these are made up of a letter, and a 4 digit number.

Given that you mentioned the fuel trims hitting 25% - I will assume that the DTCs are actually P0171 and P0174 - indicating that both banks are lean.

Often when these DTCs are set, the ECM will default to running in Open Loop - and ignore the Oxygen Sensors, until the DTCs have been cleared.

In your case, running in Open Loop is likely not safe - as it appears that your overall calibration is very lean for whatever reason.

Thanks for your reply yes you are correct on the codes, It was on original start up, there was a vacuum leak I was able to correct it quickly and the numbers normalised, completely on bank2. the exhaust fumes told me it was not actually lean. When I clear the the DTC's it did run better. I get a bank 2 knock sensor code but it has no effect on how it runs and the new one arrived yesterday I don't expect it will have an effect on the O2 sensor
I haven't adjusted much on the tune only DOD delete and increase the idle, I am open to suggestions beyond that. I know need to approach it in small steps



09 ssv wzf141 AFM off +75 rpm.hpt

[blindsquirrel]

This 10-second clip from the log is the only relevant part...

22-05-02 12-10-44 10sec.hpl

B1 O2 is flatlined at ~30mV, combined B1 trims maxed out at +50%. Then, based on apparently nothing, trims reset to zero and a full 3 seconds later, B1 O2 magically wakes up and starts switching like nothing ever happened.

You didn't happen to do anything to make that happen, did you? Like wiggle a harness, tap on something, force a fuel trim reset in the scanner...?

[blindsquirrel]

FYI, a lean idle stinks much worse than a rich idle. Rich idle just smells like.. well, rich. A lean idle will make you want to do whatever it takes to be somewhere else.

[martin_oz]

This 10-second clip from the log is the only relevant part...

22-05-02 12-10-44 10sec.hpl

B1 O2 is flatlined at ~30mV, combined B1 trims maxed out at +50%. Then, based on apparently nothing, trims reset to zero and a full 3 seconds later, B1 O2 magically wakes up and starts switching like nothing ever happened.

You didn't happen to do anything to make that happen, did you? Like wiggle a harness, tap on something, force a fuel trim reset in the scanner...?

yes I force reset the fuel trims with the scanner. the fuel trims behave after that, my suspicion although a bit far fetched is the injectors o-rings leak a little and once warmed
up and I rest the trims it works fine. I have received a new set but I won't get a chance to fit for a couple of days.

I believe it was rich had a strong fuel smell, not that I can prove it. Since I fixed the missing ground (the loop had snapped off)
and re-setting the fuel trims it no longer smells rich. but I still don't trust it, I know I should use a wideband but I don't have one.

[blindsquirrel]

It's much harder for the stock narrowband system to lie to you than it is for an aftermarket add-on wideband to lie to you. As long as the NBs wake up quickly, and they both do so at roughly the same time from cold start, and they switch at the same frequency, you can believe what they tell you. You also have the one bank to use as a plausibility check against the other bank. The WB is its own standalone thing and can easily be off in left field, many many examples of that happening here from other users, everything from broken/wonky sensors to bad math.

If two NBs act healthy, and they both agree with each other but disagree with what the WB says, you should trust the NBs.

[martin_oz]

Good to know if as I suspect the new injector seals don't help I will probably replace both sensors just in case
thanks

[martin_oz]

It's much harder for the stock narrowband system to lie to you than it is for an aftermarket add-on wideband to lie to you. As long as the NBs wake up quickly, and they both do so at roughly the same time from cold start, and they switch at the same frequency, you can believe what they tell you. You also have the one bank to use as a plausibility check against the other bank. The WB is its own standalone thing and can easily be off in left field, many many examples of that happening here from other users, everything from broken/wonky sensors to bad math.

If two NBs act healthy, and they both agree with each other but disagree with what the WB says, you should trust the NBs.

Hi I drove the car to work today to get some more data, it threw codes a couple of times on the way home "lean on bank1" (permanent) and a new one "B1S1 O2 sensor heater circuit"(permanent) this is the first time I have had that one. Watching the B1S1 voltage after re-setting fuel trims it will fluctuate from matching bank2 down to 3mv and back randomly occasionally staying there till I re-set again. My question is do O2 sensors fail like this or is it more likely to be a wiring issue


22-05-05 13-03-03.hpl

[blindsquirrel]

It could be either a sensor shorted internally from signal return to ground, or in the harness between sensor & ECM. The test for that would be to unplug the affected sensor while it's stuck at low voltage (assuming you can wiggle things enough to get it unplugged without also making the issue go away). If voltage right-quick-like goes up to the 450mV bias voltage when unplugged and then goes back down again when reconnected, it's the sensor. If it stays stuck low it's in the harness (or internal ECM fault).

[martin_oz]

Just to keep up I tried disconnecting the sensor and I got the 450mv.
I have ordered sensors but won?t see them till the end of next week. Hopefully this will help.

[martin_oz]

Thanks for the advice and support on this issue, I have had some success but still a way to go.

Update- I got my new o2 sensors (thanks Rock Auto and FedEx. It’s a long way to Australia) fitted them and I now have consistent fuel trims, looks like the obvious and kind of easy solution to my problem was it (for the first time in my life)
Motor has done 700 km so far there are a few tuning issues which I am trying to identify but I will look at other forum posts before I ask about them here