Chasing a rough idle?

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.

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

j91z28d1 said:

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.

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

Fless said:

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

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Yeah I had 6 fault codes pop up for that

Fless said:

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.

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

Fless said:

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.

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

j91z28d1 said:

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.

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

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?

j91z28d1 said:

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

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

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