Chasing a rough idle?

[Fless]

It's the upstream (pre-cat) O2s that are disconnected, right? Makes no sense that it would go into closed loop without the O2 reporting.

 

[Fless]

Also with the O2s disconnected you should be seeing O2 heater circuit fault codes.

 

[2009TahoeLT]

that's kinda weird it's still removing 8% fuel with the o2s unplugged.

is it possible to clear/reset those? I was expecting trims to be stuck at zero with the o2s unplugged.

edit, and it's in closed loop. yeah that didn't work at all lol.

They were stuck at 0 until it warmed up a bit. Then they started bouncing around again

 

[2009TahoeLT]

Also with the O2s disconnected you should be seeing O2 heater circuit fault codes.

Yeah I had 6 fault codes pop up for that

 

[j91z28d1]

It's the upstream (pre-cat) O2s that are disconnected, right? Makes no sense that it would go into closed loop without the O2 reporting.

refresh my memory. an intake leak it needs to add fuel for the extra air right?

 

[2009TahoeLT]

It's the upstream (pre-cat) O2s that are disconnected, right? Makes no sense that it would go into closed loop without the O2 reporting.

Yeah I unplugged 4 of them I believe. Might have been 3 but definitely 2 pre cat were unplugged

 

[2009TahoeLT]

that's kinda weird it's still removing 8% fuel with the o2s unplugged.

is it possible to clear/reset those? I was expecting trims to be stuck at zero with the o2s unplugged.

edit, and it's in closed loop. yeah that didn't work at all lol.

Yeah I reset the o2s before but I didn’t reset when I unplugged them

 

[j91z28d1]

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?

 

[Fless]

refresh my memory. an intake leak it needs to add fuel for the extra air right?

Yes, unmetered air dilutes the mix and the O2 sensors add fuel to compensate. Positive fuel trims.

 

[Doubeleive]

erasing a code reset's the 02 sensors, and all other emissions related stuff.

 

[2009TahoeLT]

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?

It was still running a little rough but was a little better but it was also idling at 675-715rpms at that time. Once it settled down to the 575-615rpm area it started sputtering again worse. I checked misfires again and at idle there’s no misfires even with it running rough. But once you hit about 1100-1600 it misfires on almost every cylinder but 1 I believe

 

[Fless]

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?

 

[2009TahoeLT]

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

Honestly no idea. It could have been replaced or could be oe. I have no records on it sadly

 

[Doubeleive]

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

 

[2009TahoeLT]

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

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

 

[Doubeleive]

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

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

 

[2009TahoeLT]

Also I noticed earlier when revving it to the 1100-1600rpm range to check misfires. I was getting some popping sounds from the exhaust, backfiring.

 

[j91z28d1]

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

I believe the sell a kit on Amazon that makes it easier.

 

[2009TahoeLT]

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

Found this online I can pickup tomorrow. Looks like it has the o2 adapter. If this won’t work I’ll have to order off Amazon

 

[2009TahoeLT]

O2 sensor is stuck on there pretty good. And it’s getting ALOT colder here. Might have to wait till a decent day to do it.