LT1 Diagnostic ?
LT1 Diagnostic ? Hey Everyone,
I have an LT1 F-body with OBD II. It seems to be running a little rough at idle and seems a little sluggish under all types of engine load, but all this only seems to be present when the PCM goes into closed loop. In open loop, it idles smooth and has good response through out the RPM range. I recently threw it onto a scanner and here are some of the major results I found.
It is running -15 degrees of spark advance @ idle. At 3k RPM it is running at -47 degrees of spark advance
Is this normal?
The O2 sensors showed a variation of .1V to .8V on bank 1 and from .1v to .2v on bank 2 at idle. Is bank 1 O2 sensor showing too much variation or is bank 2 lazy? Or is this normal?
Long term fuel trim for bank one was -15% and -13% for bank 2.
MAF sensor showed 9 g/s @ idle.
MAP sensor showed 41 kPa @ idle.
These were the major things that I felt were relevant to the situation. If anyone has any idea what the specs SHOULD be for a healthy LT1 with proper functioning sensors, could you please tell me if these specs are acceptable or if these are not. I truly believe that there is some kind of sensor-related issue that is causing the car to run worse when in closed loop than in open loop. Thanks so much for anyone and everyones help!
I have an LT1 F-body with OBD II. It seems to be running a little rough at idle and seems a little sluggish under all types of engine load, but all this only seems to be present when the PCM goes into closed loop. In open loop, it idles smooth and has good response through out the RPM range. I recently threw it onto a scanner and here are some of the major results I found.
It is running -15 degrees of spark advance @ idle. At 3k RPM it is running at -47 degrees of spark advance
Is this normal?The O2 sensors showed a variation of .1V to .8V on bank 1 and from .1v to .2v on bank 2 at idle. Is bank 1 O2 sensor showing too much variation or is bank 2 lazy? Or is this normal?
Long term fuel trim for bank one was -15% and -13% for bank 2.
MAF sensor showed 9 g/s @ idle.
MAP sensor showed 41 kPa @ idle.
These were the major things that I felt were relevant to the situation. If anyone has any idea what the specs SHOULD be for a healthy LT1 with proper functioning sensors, could you please tell me if these specs are acceptable or if these are not. I truly believe that there is some kind of sensor-related issue that is causing the car to run worse when in closed loop than in open loop. Thanks so much for anyone and everyones help!
the scanner has to be reading it wrong. it won't retard 47 degrees of timing. .1 to .8 is normal , the other sensor might be going out or that bank is running lean. as far as how much gps the maf will see depends on weather or not you have a cam/heads/stroker or stock. my idle is around 1000 and my map sees around 71 kpa, my maf sees 19 to low 20's at the same idle rpm. thats a 383 though, that still needs some tuning.
I had a feeling one of those O2s was off. As far as the timing, I need to look into that some more. I am using a software program called "PCMSCAN". Thanks a lot guys. BTW, I am running a pretty much stock motor. Only mod is a cold air intake, the motor has 97k on it.
Originally Posted by jasonisdn
the scanner has to be reading it wrong. it won't retard 47 degrees of timing.
47 deg is the commanded advance, the actual amount is that minus any retard.
Your timing advance doesn't matter as much. What you want to look at in your scanner is the amount of retard you are getting.
i wonder how he is seeing 47 commanded advance. we went though my pcm with the tuner and the highest advance was 44, that we saw in the stock table. that was in the 4000 rpm to 7000 rpm table. the 400 to 4000 was slightly lower than that.
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when we were working on my car we noticed we had it set at 38 max and were seeing 42 in 1 area. we were using tuner cat and couldn't figure out were the computer was getting the extra few degrees. we went through about 10 other tables looking for a reason, none could be found.
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