2007 Tahoe Misfiring Badly

[qednick]

Hi everyone, just joined this forum to see if anyone can help throw some light on diagnosing this problem.

My wife and I bought a 2007 Tahoe LT (5.3 gas w/AFM, 110K miles) about 4 months ago. No real issues at all until yesterday morning OTW to work dash came up with stabilitrak/traction control warnings and flashing engine light. I pulled over and it was misfiring so badly it almost stalled. Made it to work but had to put in neutral at every light to prevent possible stall.

Took it to local autozone to get error code. Showed misfiring cylinder one. Changed out plug for brand new irridium one (cheapest potential fix) on that cylinder but no joy. Hooked up spark tester to plug and see it's sparking OK.

So is it safe to rule out plug, plug wire and coil?

I'm thinking about switching out the fuel injector next. My big worry is a lifter problem since it seems these engines are prone to that. However, there's no noise, tapping or rattling.

Also, a couple of weeks ago, the engine light came on and code said running lean. I added some fuel injector cleaner to tank and light went out immediately. I also added a can of seafoam to the tank last week for good measure.
Since I had the lean code recently, and since there's no rattling or tapping noises, does switching out the injector make the most sense at this point?

I've heard there's a tiny filter/screen for each injector that can get clogged/blocked with rust or debris. Does anyone know if this screen is actually in the injector or is that external to it? My wife has a tendency to run down the gas to almost empty (I'm always getting onto her about this), so I'm wondering if the recent seafoam/cleaner has loosened some debris and clogged the injector or screen.

At this point I'm mostly worried about the potential lifter problem and the amount it will cost to fix that. Right now I really just need to try eliminating the easier/cheaper potential issues before assuming the worst.

Any other potential causes besides injector or lifters? I would assume bad fuel pump or throttle body wouldn't cause issue specific at just one particular cylinder?

 

[Eastends]

Humm i hope its not the case for you but read up on 5.3 with afm problems

If you can do a compression test on cyl 1 and 7

 

[qednick]

Yeah my biggest worry is the AFM lifters. Though [mostly] everyone reports noise with them and we definitely have no noise...which is throwing us off.

 

[2007tahoe]

Do a compression test on that cyl. Prob will not even take 5 min. You can rent one from the parts store if you do not have one. If the compression is good, one easy trick is to swap out the coil with another cyl and see if the problem follows. Just because it has spark does not mean it cant be weak. I Have rarely seen bad injectors, but it is possible.

 

[Steedog]

Did this ever get resolved? I had a similar issue that 07burb helped me with. I am certain we had identical problems

 

[TraumaTruck1]

I had this issue on my Yukon with the 6.2. Didn't have compression, and it ended up having a broken valve spring. Mine doesn't have the AFM, but they symptoms of the running rough and missing were the same.

 

[Rexter]

I had this issue on my Yukon with the 6.2. Didn't have compression, and it ended up having a broken valve spring. Mine doesn't have the AFM, but they symptoms of the running rough and missing were the same.

yup mine did the same all. Valve wide open no compression.

 

[qednick]

Sorry for the late response on this but it's taken several weeks to get things right.

I was hoping it may just be a valve spring or something fairly easy but alas it was one of the AFM lifters collapsed (cylinder 1). We bought a full AFM lifter kit off amazon for approx. $500 (comes with all new AFM lifters, gaskets, etc.). Also bought a new VLOM (valve lifter solenoid cover that sits between the heads--the oil pressure sensor fits into this). Apparently the VLOM is STRONGLY RECOMMENDED to prevent the same issue from happening again just a few thousand miles later!

So we pulled the heads (best to do both I guess!), replaced the lifters, VLOM, gave it all new oil. Engine is running sweet! However, had some other things to take care of: all new tires, new brakes, also replaced the front sway bar links. Car literally drives like new now.

However, one more thing:

I also found a gizmo on Amazon that you plug into the diagnostic port under the dash that prevents the AFM from ever activating (ie. it never goes into V4 mode). I can't remember what it's called exactly but I know it has the word "Range" in the name. It was less than $200.
The reason I'm mentioning this is because after plugging that in, it stays in V8 mode all the time so IT DRIVES LIKE A V8!! Prior to that, it was like a big slug. Now it's responsive and drives fantastic! Also, if I'm not mistaken, it actually uses less gas!

Anyhoo, I wish we had known about this gizmo before because if we had had one, the lifter may never have gone out on us in the first place! I figured for the extra 190 bucks or so, it will prevent the same issue from happening again AND make the car more pleasurable to drive.