6.2 High RPM Misfire

[sealandsky]

I noticed that also, but my hunch is without the maf working, running 100% on speed density those tables werent dialed in real close in the tune.

Thank you! Question: If you were running the same scan on your LT-4, what would the LT fuel trims look like?

 

[Doubeleive]

Thank you! Question: If you were running the same scan on your LT-4, what would the LT fuel trims look like?

keep in mind out of spec fuel trims are a symptom, not the cause. (like a runny nose is the symptom of a cold)
in any case you will need to dig deeper to find the cause


These number are not set in stone there just for reference, the fuel trims can be reset and will self relearn, seeing something like 12% is not necessarily bad thing they average out

• Ideal Range: Between -5% and +5% is considered healthy and indicates a well-sealed, properly functioning system.
• Acceptable Range: Between -10% and +10% is generally not enough to trigger a Check Engine Light (MIL) but may suggest a very minor vacuum leak or aging sensor.
• Total Trim (Short Term + Long Term): You should look at the sum of both values. If Short Term is +3% and Long Term is +2%, your total trim is +5%, which is perfectly normal.
  
  

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  • Fault Threshold: GM typically sets the threshold for a "Lean" (P0171/P0174) or "Rich" (P0172/P0175) code at around ±20% to ±25%.
  • Positive Trims (+15% and up): This means the computer is adding extra fuel to compensate for too much air. Common causes on the L86 include vacuum leaks, a dirty Mass Air Flow (MAF) sensor, or a failing fuel pump.
  • Negative Trims (-15% and down): This means the computer is cutting fuel because the mixture is too rich. This often points to leaking fuel injectors or a restricted air intake.

 

[randeez]

Thank you! Question: If you were running the same scan on your LT-4, what would the LT fuel trims look like?

LTs should also be near 0. and definition of 0 being +/- 3% is fine

what you have is the MAF and speed density (vve tables) set in the tune. this is what the ecu starts with for fueling if no other factors
the STs are the immediate o2 reading, after you have so many error corrections that correction gets moved to the LTs.
then you have whatever the tune whats to fuel at with addition/subtraction of the LT trim. then the ST should be closer.

so what yours is showing whatever the tune wants to fuel at is subtracting 18 (%) (rich) and then at that point the ST is saying another 3% too rich, but because its a snap shot it may be going +/- 3 so it hasnt moved to LT


the tune on mine is a little different, it disregards the narrow band o2 sensors at anything in power enrichment(PE) so they both go to zero looking at a log from mine. but i also have port injection with widebands.