25% ltft

[joecar]

ok, am I thinking this correctly...
The ECM thinks there is LESS air going into the engine. In other words, there's MORE air going in, the ECM doesn't know about.
So with O2 feedback trying to maintain commanded 14.63, it reads this additional air and therefore tells the ECM we need more fuel to maintain stoich?
That's why my trims were going so positive?

Yes.

[KCG]

ok cool. I really appreciate the lessons. Thank you.

So, is this procedure I posted earlier the correct way to force SD if I just want to get rid of the MAF at least temporarily? Not physically, I would still use the IAT right? If so, I don't understand what D is asking to do.

A. C2901: MAF High Frequency Fail 1: Change to 1 Hz
B. C2903: MAF High Frequency Fail Limit: Change to 1
C. Copy B5913 High-Octane Spark to B5914 Low-Octane Spark
D. Insure MAF Sensor Circuit is displayed as a current DTC

[joecar]

Yes, you always want to use IAT.

A and B are setting the MAF fail parameters to make the MAF "fail" immediately...
when the MAF "fails" it causes a DTC to show up, this is what D is asking you to verify;

the presence of a MAF DTC indicates that the PCM has abandoned the MAF and is running from VE only.



When the MAF DTC shows up, the PCM now does a few things differently:
- it now runs from the LO Spark table B5914,
- it now run from the Backup VE table B0103 if it exists,
- it may now ignore the knock sensors,
- it may now set the trans line pressure to max (see P0101-3 in tables E0102,3,4),
- a few other things possibly (most likely).

[KCG]

All great info Joe.

- B0103 does not exist in my tune (ECM?)
- Is there a "systems check" or way to verify KS are working?
- E0102 etc are all set to NO

[joecar]

B0103 is the Backup VE table that exists in all the LS1A and a few LS1B calibrations.


To verify that KS are working, try this (works only on some LS1B's):
ignition key on, engine off,
log the pids GM.ESC1DNL and GM.ESC2DNL,
knock sharply on the front of the cylinder head with a larger wrench (say 20mm combination) or the smallest sized ball-peen hammer...
sometimes you will see activity on one or both of those pids.


MAF DTC's in E010x set to No: ok this avoids the PCM setting trans max line pressure and/or trans fault state when the MAF is in failed state... but do monitor line pressure by logging the pid GM.TFMPRS.psi), make sure that goes up easily/quickly with throttle.

[KCG]

B0103 is the Backup VE table that exists in all the LS1A and a few LS1B calibrations.


To verify that KS are working, try this (works only on some LS1B's):
ignition key on, engine off,
log the pids GM.ESC1DNL and GM.ESC2DNL,
knock sharply on the front of the cylinder head with a larger wrench (say 20mm combination) or the smallest sized ball-peen hammer...
sometimes you will see activity on one or both of those pids.


MAF DTC's in E010x set to No: ok this avoids the PCM setting trans max line pressure and/or trans fault state when the MAF is in failed state... but do monitor line pressure by logging the pid GM.TFMPRS.psi), make sure that goes up easily/quickly with throttle.

Quick update..
Added the pids and rapped on the passenger side head a few times. Did not get any counts.
Added trans pressure pid and can see it jump quickly as throttle increases but drops to zero soon as input stops (steady state throttle). I assume this is correct response.
So, MAF is failed, Hi octane table copied to low. Started the engine and after warmup, STFT are in the -10% range. This is at idle. Wasn't able to drive for other reasons.
Replaced B3701, B4001, B4003-5, B4307 with data from the original tune (LS3 data instead of band-aid LS1 data). Now at idle, I'm about 13-14% positive
I'll be able to drive it some and log tomorrow.

[KCG]

Cold start. About 30 minute drive. Trims still plenty positive.

[joecar]

Look at the VE table where the LTFT's are positive, and remove about that much %.

[KCG]

Is it common for a mail order tune to be this far off? I'm at +25% a good part of that log..even with MAF failed

[joecar]

Usually they're closer than that (some MO tuners are very good, they have figured out the right questions to ask)... there are some bad ones... and then sometimes stuff just happens.