Misfire

[HiHoeSilver]

Oh ok I understand. I cant find a vacuum leak anywhere. Are there any common leak areas for the bank 2 side?

Intake gaskets

 

[bigfootchiro]

I did because he showed us +8-9 at idle and back to 0-3 at 2500 rpm.

Right, because fuel issue will cause FT to climb due to excess air vs not enough fuel. Forgot about that part. Still new to FTs

 

[HiHoeSilver]

Right, because fuel issue will cause FT to climb due to excess air vs not enough fuel. Forgot about that part. Still new to FTs

Exactly. At idle, they look the same from a fuel trim perspective.

If you get on the throttle, a vacuum leak will "disappear" in the trims (back towards 0) because you're straying from stoich. A fuel delivery issue will be magnified (get even higher) because it's trying to keep up with the demand.

Of course, we are watching the STFT at this point for the instant reaction, but the same will be evident on the long term.

 

[callahan347]

I have gone over again and again with propane starting fluid and brake cleaner and get zero reaction at an idle. I understand that vacuum leak makes sense but for the life of me I can not find one.

 

[callahan347]

So update... the exhaust flange gasket behind the cats was leaking. Pulled apart to replace it and saw that the cat for bank 2 was broken up and mostly in sideways. I'm assuming it broke due to backfiring on cylinder 2 and 4. I removed the honeycomb and put the exhaust back together. Still have a random misfire but bank 2 fuel trims are back down to where they should be