fuel trim and afr
- Thread starter withku
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thanks. i’m chasing random misfires on all cylinders, not enough to trigger a code.
little bit off topic , how much vacuum should crankcase have?
i have UPR’s dual valve catch can and hi flow pcv fitting, and noticed the vacuum is a lot stronger with UPR’s.
i have worries a pcv system without a valve could cause issues. it doesn’t close under boost (there is a check valve in the line) , but theoretically could let excess air into the intake?
Bluezone
Tailgaters will be prosecuted.
What's the Lambda supposed to be like at wot? I'm seeing nothing better than.82 average. I realize we don't want too much fuel going to the cats and melting them down. Just that at 14 or 15 lb of boost, I thought they'd be closer to.78-.75.
Jordan_R
Stock Block Ready To Knock...er..Rock
.82 is basically where everyone runs them at wot. Some go from .82 to .85 in the top end when chasing all the power
At cruise the system constantly oscillates between .99 and 1.01 lambda. Those fuel trims are typical. Those AFRs are too high unless you're running ethanol free fuel, but that's most likely just a logging or PID conversion mistake as I don't think the ECU actually spits out anything in AFR.
You will not go lean from vacuum leaks. This is a speed density system so everything is based off manifold pressure. Excess air in intake -> higher manifold pressure -> more fuel. Though if it's bad enough that the throttle can't control engine speed then you could end up in a fuel cut or fuel enleanment torque control mode. There are PIDs for torque source, throttle angle source, spark source, fuel source etc. to tell you if that's the case but not sure if they're accessible with forscan.
You will not go lean from vacuum leaks. This is a speed density system so everything is based off manifold pressure. Excess air in intake -> higher manifold pressure -> more fuel. Though if it's bad enough that the throttle can't control engine speed then you could end up in a fuel cut or fuel enleanment torque control mode. There are PIDs for torque source, throttle angle source, spark source, fuel source etc. to tell you if that's the case but not sure if they're accessible with forscan.
i think it’s accurate, put my stock pcv valve on and now i’m running 14.1 - 14.5 , and it’s more stable. fuel trim is now +7% average vs +13%.
i’ve only done a few logs so far, so not concrete.
Stock peaks at .73 IIRC. And actually you've got it backwards, you dump in more fuel to cool things down. Combustion temperatures peak at stoich and fall as you move away in either direction (rich or lean). In the factory calibration, catalyst overtemp protection triggers a .68 lambda target.
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