2022 Tahoe random misfire

MixedQiwi · June 30, 2024

Hello everyone. Came here with 2022 tahoe GM 6.2 L87 engine problem. 4th cylinder randomly misfires without MIL. When it came to us two months ago it was randomly misfiring by all of the cyilinders, but 1,4,7 were the most. MIL was shown up. Since then we found melted catalytic converter on the left side (1,3,5,7) and changed it. Checked cylinder compression - it is approx. 220 psi (15.5 bar) in every. Changed all of the injectors. Changed all of the spark plugs, wires and coils. All of the spark plugs were completely worn. Now it has only one problem cylinder. It could work without misfire for 1-3 hours staying at idle or start to misfire when accelerator slowly and gently pushed towards to reach approx. 1.5-2k rpm doing 6-25 misfires per logging cycle. No tickling noise. Opened both rocker covers to look at the lifters. They are not stuck when engine is idling. When pushing accelerator fast and completely, or just sharply and briefly push - there are no misfires at all and it stops misfiring if there are some. Total mileage is 25000 miles. 13000 miles ago it had stuck lifter on the right head (2nd cylinder, intake valve). Since then, all of the lifters on the right head have been replaced. Oil pressure is 40 psi at cold engine and 30 psi at hot. Fuel corrections are: -0,5% long bank 1 -1% - -4% - -7% long bank 2 (high percentage when misfires obviously from enriching the mixture with unburned fuel) Short-term correction jumps from 1% in plus to 5-7% in minus, depending on misfires in right bank. Coolant level is constant i guess. Camshaft without any scratches or damages. Could new injector be broken by the chance? Will try to change 4th injector on monday and swap 4th and 3rd AFM system solenoid but it hardly would work. I'll be glad to hear your opinions.

Edited June 30, 2024 by MixedQiwi

asilverblazer · July 1, 2024

Swap injector from a good cylinder to the bad one. See if the miss fire follows.

Make sure they are legit GM injectors!

Smoked CAT probably from running with the miss too long.

ScathaTheWorm · September 12, 2024

Could be the injectors or even the spark plugs. Replace them ASAP..will help avoid a problem

Also, USE PREMIUM FUEL ONLY. and change oil+ filter using right type every 3k-4k miles...

DIY Mechanic Mike · June 14

Misfire Diagnosis and AFM Lifter Insight

Your issue sounds similar to my misfire issue which turned out to be caused by an AFM lifter that was misaligned inside the lifter guide. This happened after I rebuilt the cylinder head due to a faulty lifter in the first place. Once oil pressure built up, the misaligned lifter would deactivate on its own without a signal from the solenoid, which led to the misfire.

From what I understand, the L87 engine uses AFM lifters on all cylinders as part of the more advanced DFM (Dynamic Fuel Management) system, compared to the simpler AFM setup in my 2011 Yukon Denali 6.2L. However, the diagnostic process should be similar.

How to Check If Your Lifters Are Working Properly

Remove the valve cover
Start the engine and observe the rocker arms at idle
The rocker arms should move up and down normally as the valves open and close. If a rocker arm stops or has insufficient moving after a few seconds or minutes, this usually indicates a lifter issue.

Possible Causes

Misaligned lifter
Faulty lifter
- Weak spring that no longer meets pressure specs, causing premature deactivation
Broken lifter
- lifters are a complex creation and have many moving parts which can break fall apart or get stuck
Worn or damaged lifter guide
Issue in the valley cover
- Bad solenoid
- Solenoid not managing oil pressure correctly
- Loose solenoid bolts, which can cause pressure loss (in my case, I was able to remove the first three bolts by hand due to looseness)
- Restricted oil flow to the lifter
Worn or damaged camshaft
This one I haven’t had the chance to personally deal with yet.

If you have good compression, it usually rules out most valve-related mechanical problems and points more toward lifter or camshaft issues.

You can safely perform this check while the engine is idling. Unplug the fuel injector connectors on that bank, or for a less invasive approach, pull the injector fuse to prevent raw fuel from entering the cylinders during the test. There’s no need to remove the spark plugs; they can stay in place.

If the issue is intermittent, it’s less likely to be electrical and more likely related to oil pressure or premature AFM or DFM deactivation. This could be caused by a lifter with a weak spring, a damaged or worn lifter guide that no longer holds the lifter in place, or a lifter that has already shifted out of alignment. I assume you did not do a head rebuilt and did not get it machined as this is also possible angle.

FYI I performed all the usual steps of replacing fuel injectors, testing fuel injector resistance, testing spark plugs, replaced spark plugs just in case, spark plug spacing, replaced ignition coils and wires, replaced valley cover with new solenoid and ran compression test to confirm everything. None of this was my issue.

I wish someone had shared this with me when I began my diagnosis. It would have saved me a lot of time. Hopefully, this helps point you in the right direction.

Edited June 14 by DIY Mechanic Mike