Running a Vortec 5L with a 5.7 PCM..

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Jesse_Wenting

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Been using the PCM from the parts truck the 5L was in for a few months now, but it thinks I'm geared to 3.73 and am running 254/75R16s (30.5s). The 5.7L PCM (which is now back in the truck with the 5L engine and running) obviously thinks the engine is bigger, but is correctly programmed for the 3.42 gearing, and thinks I'm on 265/75R16s (31.5s).
I'm actually driving on 285/75R16s (33s) so the 5.7L PCM is closer than the 5L PCM

I switched back to the 5.7L PCM because I was using a lot of fuel. Like average 8mpg some days, but then sometimes at highway seed I'll average 20mpg... Oh also both engines are Vortec, duh, and both are 1998

I know running the 5.7L PCM will cause me to run a little rich but does anyone know if it's better than the PCM having the wrong final gear and thinking the tires are way smaller? Also anyone know if the PCM will realize it's running a bit rich and correct the mixture on its own?
 

Schurkey

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The O2 sensor should provide at least some correction to the fueling.

You need to get the correct parameters loaded into that computer. It will never be right without that.
 
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