Monte Carlo bad fuel air ratio
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Joined: Sep 2023
Posts: 8
It was continuing to rack them up with the MAF connected. It did not have any when I ran it with the MAF sensor disconnected.
One thought with it being only cylinders 3 and 6, was could there be an internal leak in the plenum that could be making those two cylinders AFR go crazy? I'm not certain what all seals off inside the plenum to the lower intake. Could cylinders 3 and 6 be getting more than their fair share of any EGR thats coming in?
Ok, so since the 02 is bouncing is not an issue, it would only be an issue if it was more constant at one end of the range?
I believe that was long term but would have to double check my notes. I was debating on pulling the intake off and having a look at the gasket to see if anything was wrong. Now that the problem seems to be indicating cylinders 3 and 6 have the issue, I'm not sure what else could be causing that. I do have a different ignition control module I could swap in. Maybe a bad/intermittent connection to the coil pack or something internal is wrong with the ICM?
Thanks again.
One thought with it being only cylinders 3 and 6, was could there be an internal leak in the plenum that could be making those two cylinders AFR go crazy? I'm not certain what all seals off inside the plenum to the lower intake. Could cylinders 3 and 6 be getting more than their fair share of any EGR thats coming in?
Ok, so since the 02 is bouncing is not an issue, it would only be an issue if it was more constant at one end of the range?
I believe that was long term but would have to double check my notes. I was debating on pulling the intake off and having a look at the gasket to see if anything was wrong. Now that the problem seems to be indicating cylinders 3 and 6 have the issue, I'm not sure what else could be causing that. I do have a different ignition control module I could swap in. Maybe a bad/intermittent connection to the coil pack or something internal is wrong with the ICM?
Thanks again.
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Joined: Sep 2023
Posts: 8
Ok, so the new MAF sensor arrived today and I just installed it. The car runs fine at low speed but when you peg it for the passing gear it is still doing the same thing. It had a P0102 code for the MAF sensor circuit. I still hear a bit of a whistling noise when I get it to the higher RPM's. Do you think it is worth pulling the intake and throttle body and just checking all of that? Is there something else that I should be looking for?
Thanks
Thanks
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Joined: Sep 2023
Posts: 8
Was it continuing to rack up new misfires or were they all historical?
Being too far out of whack on AFR can certainly do that - but its puzzling that its only on 2 specific cylinders. Generally if AFR is getting to the fringe, you'll start seeing it everywhere.
Its also suspicious that its happening on cylinders that share a coil pack (although I know you swapped it with no result). Not sure what to make of that.
The hard part is if its actively misfiring, thatll skew fueling (as you're dumping a bunch of raw o2 into the exhaust). In this case, the O2 is oscillating around stoich and the trims aren't maxed (ie if the pcm saw it was still too rich, it could pull more fuel from the base map to correct- but its not as it sees its able to achieve stoich). So that makes me think we need to focus on their misfires next.
Since the pcm is seeing over fueling and there aren't a lot of causes there - Id probably try swapping injector locations. Stick injectors 3 and 6 somewhere else and see if the misfires move.
That sounds about right. The AFR range that represents is very tight. Its concerning when the O2 sensor pegs to one side or the other.
Short or long term trims? Negative 19 is really high and is close to tripping a code (I think -22 is the trip point). Thats pulling an awful lot of fuel - we just need to figure out why.
Being too far out of whack on AFR can certainly do that - but its puzzling that its only on 2 specific cylinders. Generally if AFR is getting to the fringe, you'll start seeing it everywhere.
Its also suspicious that its happening on cylinders that share a coil pack (although I know you swapped it with no result). Not sure what to make of that.
The hard part is if its actively misfiring, thatll skew fueling (as you're dumping a bunch of raw o2 into the exhaust). In this case, the O2 is oscillating around stoich and the trims aren't maxed (ie if the pcm saw it was still too rich, it could pull more fuel from the base map to correct- but its not as it sees its able to achieve stoich). So that makes me think we need to focus on their misfires next.
Since the pcm is seeing over fueling and there aren't a lot of causes there - Id probably try swapping injector locations. Stick injectors 3 and 6 somewhere else and see if the misfires move.
That sounds about right. The AFR range that represents is very tight. Its concerning when the O2 sensor pegs to one side or the other.
Short or long term trims? Negative 19 is really high and is close to tripping a code (I think -22 is the trip point). Thats pulling an awful lot of fuel - we just need to figure out why.
I checked the MAF wiring by back-pinning it, but I did NOT clean the electrical contacts or assure that the pins are squeezing tight on the male pins. I am going to do that tonight.
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