Chasing a rough idle?

j91z28d1 said:

I've used the test before on older trucks at work to test of something is bad. usually you can unplug it, it default to a set value and judging by if it runs better or worse. it can help you what a direction to go in. but since I've not actually tried it on my own gm truck, is it possible it can look at the rear o2's if the front are disconnected? new one in me.


either way, my thinking is your ecm is removing 8% long term and 8% short term. that's enough fuel removed its going to run bad from being lean even if everything else is correct. so need to find out why it's doing that.

did you notice if it ran any better while the trims were at 0 while warning up?

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Fless said:

I read that you did the crank sensor relearn, but do you know if that's an OE sensor? Or if it's ever been replaced

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Doubeleive said:

I would still a do a backpressure test if a cat is clogged it will cause the misfires that are otherwise unexplained
2.5 psi is max allowable, mine had 5 psi at idle and 10 with throttle. drove normal around a city street but no power, gutless wonder

not sure if it helps but
mine didn't show up until higher rpm's (under a load) but it translated into knock retard, skip to about 1:40
I could barely get it to go over 80-85

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2009TahoeLT said:

I’d have to go buy a gauge to test it. I can try and get one tomorrow

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2009TahoeLT said:

I’d have to go buy a gauge to test it. I can try and get one tomorrow

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Doubeleive said:

you should be able to find something at harbor freight or make one out of stuff found there.
just needs to fit in the pre-cat 02 sensor bung
it could be something else but probably a good idea to rule it in/out as part of the troubleshooting process

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