Any help would greatly appreciated

[Kedo]

Hi y’all. I have a 2007 Tahoe flex 5.3 with 148k. Just bought the car a couple weeks ago. The previous owner didn’t know much about it but it had a p0301 cylinder 1 misfire with stabiltrack and flashing engine light. So I did my part and went and replaced coil pack, spark plugs, swapped wires around from 1 to 5 and no change. So I popped the valve cover off, inspected push rods on #1, they weren’t bent but thought while I’m here, I put two new push rods in. Still had the misfire. Next I pulled the driver side fuel rail, noticed #1 was a little dirtier then the others so I went down and bought a new injector. Still had the misfire on #1 cylinder. So over the weekend I pulled the head, took it to a machine shop and had them inspect the lifters weren’t bad(but did swap the intake and exhaust lifter around), the valves, springs, guides and everything came back 100%. Put everything back together yesterday. Fired it up and boom no misfire and ran like a champ. Then this morning on my way into work it reared its ugly head. What did I miss or what else should I be looking for? Map and maf are also replaced. Could it be rocker arms? Valve cover itself?

Any and all help is greatly appreciated.

 

[Kedo]

I also wanted to add that a compression test was done and got 90psi on #1, cleared it and bumped it a second time and got 120psi. Checked #3 cylinder and it also had 120psi.

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

I cannot personally assist you with your issue, but other members of this Forum much more knowledgeable than me in this area will chime in.

 

[TollKeeper]

Sounds like a faulty (as usual) AFM/DOD system. Best to get it tuned out, or do a complete AFM/DOD removal. I got it tuned out, and had no issues. But the faulty system is still there, and can rear its head at any time.

 

[B-train]

If you are dealing with an intermittent AFM issue, make sure the oil is clean, and that the pressure is good. The oil pump pick up tube o-ring gets cracked with age and heat and will suck air. Ive also heard of issues with the VLOM, but have no experience with that. Just some things to check.

Another option is to substitute 1quart of oil with Marvel mystery oil, or dextron 3 atf. Both are high in detergents and will help clean sticky lifters, etc. I've done this for years with great luck......just cleared up a noisy lifter on my daughter's 2008 lucerne 3.8L that we got from in-laws that were poor with maintenance. Quiet as amouse again.

I usually put in ATF once or twice a year in both of my yukons as a normal maintenance routine. Usually for the last 1000 miles of the oil change before dropping it.

 

[Dustin Jackson]

@Kedo There are many parts to the AFM system that could contribute to these problems so most people recommend just getting rid of it, if you've done all this work without replacing the VLOM that could be your problem but at this point I would go for an AFM delete and just install standard cam, lifters, valley cover, and tune AFM out and would give your best bet. Doing that work would also thoroughly cover any of the components that could be attributing to your problem.

 

[Geotrash]

A cheap way to test out the AFM root cause theory is to buy an AFM disabler device. If it solves the problem then you can have AFM tuned out in the ECM. But whatever you do, do it quickly because a malfunctioning AFM system is a ticking time bomb. It's only a matter of time before a lifter gets stuck in transition and you start breaking hard parts in there.