Help with LQ4 misfire
Thread Starter
Teching In
Joined: Apr 2019
Posts: 3
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Help with LQ4 misfire I'm having a very rough time with my '02 2500HD. It likes to misfire on cylinders 2 and 6 usually, but will randomly hit all cylinders under light load. Free revving around 1k and the misfires go nuts. Above that, at all throttle positions, runs like a champ. It will also run between 5 and 10% lean on either bank and any time. I've gone through the injectors, coils, plugs, wires, PCM, O2s. I just did intake gaskets, new exhaust manifolds and gaskets, and cat delete. Fuel pressure is good, holds steady at 59 psi. Air flow sensors are good. Any advice would be much appreciated.
TECH Apprentice
Joined: Sep 2016
Posts: 347
Likes: 10
Hard to say, really. Sounds like to me, if everything is OE:
1) Something wasn't torqued to spec, allowing some sort of vacuum leak being pulled in Post-MAF, meaning you're getting more air than the MAF is picking up
2) Have you verified your MAF is in good working order? As you know, a bad MAF sensor or a dirty one will cause misfires.
I'm leaning towards a bad A/F ratio causing your misfires, if everything is stock, with a stock tune.
Also curious... do you know what caused your original manifold to just crack?
1) Something wasn't torqued to spec, allowing some sort of vacuum leak being pulled in Post-MAF, meaning you're getting more air than the MAF is picking up
2) Have you verified your MAF is in good working order? As you know, a bad MAF sensor or a dirty one will cause misfires.
I'm leaning towards a bad A/F ratio causing your misfires, if everything is stock, with a stock tune.
Also curious... do you know what caused your original manifold to just crack?
Thread Starter
Teching In
Joined: Apr 2019
Posts: 3
Likes: 0
Sadly, I don't know what caused it to crack. The MAF is in good working order. Honestly, I think I've tracked it down to defective intake gaskets. I'm going to try FelPro Permadry here in about a half hour.
