Very high long term fuel trims

TheBoomSpoon

Does anyone have any ideas on how my Long term fuel trim's can be 28-30% on bank 1 and bank 2 but yet live monitoring of the AFR during tooling around town as well as WOT is well within spec. WOT throttle a bit on the rich side around 11.6 and tooling around generally flopping between 14.3 to 14.7. Completely off throttle is 29 which I assume is normal?

Monitor test for emissions show all systems good, I'm using ODBLINK software on my android phone to test for emissions as it runs the test to spec for each state's requirement and for MD I show ready for emissions so I think that is good. Obviously I'm throwing Codes for "system too lean" in P0174 and one other one is which is lean also.

I just can't rationalize in my brain how the real-time view of the AFR never gets out of line yet the long term fuel trim is so high, monitoring of the short-term trims seem to bounce around -5.6% and 6% which to me seems Ok nothing extreme but it puzzles me how if the short terms are never out of line by that huge amount how in the world can the long term trims be so bad?

anyway, anyone with any insights , I'm figuring a bad o2 should give outrageous for short term also.

Thanks
Kevin

visconti

Can you post up a log?

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TheBoomSpoon

Yes. I just had one but i mistakenly closed cipher b4 saving the logs. I did notice at low speed tooling around afr b1 and b2 trim adjustments like 120% at 14.7 afr which is richening up bot leaning out so now wonderi g if that lean code is even legit.

Ill log it again tommorow during lunch and not forget to save em b4 closing out.

DOOMMONKEY777

Ur O2 sensor, check voltage on log ranges must be btw .1-.9volts, best to do that is to log from cold start and see how it behaves.

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Jordo!

Mods?

Assuming sensors are all good, I'm thinking big vac leak somewhere and the O2's are adding in tons of fuel to compensate (i.e., high positive trim means O2's are reading lean).

Any other codes? Like slow sensor response/heater circuit? MAF codes? Have you had the primary O2's in and out recently?

Short term trims will be small because the LTFT is handling all of the constant correction, so the STFT's will be simply hovering around the overall correction of the LTFT's.

Can you reset your trims to zero? If so, you will probably see massive STFT's initially.

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SouthArk370Z

IIRC (but it's been a while since I looked), the FSM has a pretty good description of how fuel trim is supposed to work. Might give you some clues as to what's going on.

My guess is that the ECM is seeing some spikes from an O2 sensor. Eg, there is a post on this site about someone getting extreme readings when an O2 sensor wasn't fully warmed up. If you can't find it using the site's search, try one of the major search engines and add "site:the370z.com" to your search string.

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TheBoomSpoon

Here is a log from a quick WOT throttle in 3rd gear from about 52mph to 82mph. Mine is the 7AT, the car really runs well, feels great just concerned about these lean codes. I think the tuner has it rich because it leans out so much on the top end so from my novice opnion it seems to need to be richer so it can lean out safely but it appears to just be doing too much on the trim. Anyway, attached are the is a CSV log of that run, I left the Fuel map, fuel compensation and MAF tables open so the tracer values would be included in the log.

Be aware I'm not changing anything at this point, just simply trying to make some sense and determine if I'm at any risk running it in this configuration.

These are the engine related modifications:

AAM true dual exhaust 2.5
AAM Cold-air Intakes R-Line (2.75)
Motordyne M370 manifold
AAM VQDE35 test pipes
Z1 headers


thanks for any input. Rename the attached file with .CSV then open.

Attached Files

3rd gear wot 711.txt (5.6 KB, 27 views)

visconti

I'm afraid it's hard to tell what's going on with the very limited data you provided with your datalog.

All I can see if that you air fuel target never really matches your actual air fuel ratio, looks like sloppy tuning more than anything else.

Car is going leaner in the upper rpms but again with the limited data you sent me it's hard to confirm what's going on

These cars don't have closed loop fueling during Wide-Open-Throttle so the car won't be adding or removing fuel if the car starts to go lean or rich under full engine load... If the car has a learned fuel trim that falls under the higher engine load section of closed loop learning values then you could have a fuel trim effect WOT, but it's going to effect the entire run, not just the end of it.

John

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TheBoomSpoon

John, thank you for the input. One final question for you, if the actual AFR is lean of the target AFR can that trigger the p0171 or p0174 (too lean) even though the lean condition is not a dangerous lean condition but simply lean of the target AFR?

Thanks
Kevin

TheBoomSpoon

This is above my level so i just caved in and spent the money to have it tuned at AAM. problem solved