2012 Suburban Misfire #5 drama

[Keiterburb]

Hello, 2012 Suburban 198,000 miles Vin 7 LC9 5.3 completely stock config and parts having P0305 CYLINDER 5 misfire with misfire felt at idle and smooths out under throttle. Recently began also seeing P219A. Under idle and cold temps in Wyoming the traction control will alert and turn off until rpm’s increased.

Began by pulling #5 plug that looked carbon fouled black but dry. Swapped plug, coil , wire with #3 that was burning clean. No change in condition.

Cleaned stock Air Filter, Removed and cleaned throttle body and intake of a little pcv blow by oil. No Change

MAF sensor intake flow side looks a little black but reading on live data. Fuel pressure 43-58psi, Short term fuel bank 1 was -7 to -12 during test drive.ECT sensor was reading appropriate temps.

Removed valve covers and used starter relay to crank and observed all rocker arm moving, all had same 1/32” slop when not compressed.

Removed all plugs and ran compression test most cylinders including #5 were at 150psi +\- 10psi. Failed at this point to perform leak down test as I felt all lifters were doing their thing and I am shadetree mech.

Replaced all 8 plugs and wires, removed intake manifold and replaced gaskets with metal Fel-Pro after cleaning. Replaced all 8 fuel injectors with stock GM replacement from rock auto. Throttle body gasket as well.

No fuel leaks and fired right up post install but remained with same misfiring #5 only now my back felt broken as a result . Wiggled injector wiring from top to bottom while running with no change at idle misfire.

I am assuming next test will be cylinder leak down check and will be my first time trying that.

Any help would be greatly appreciated!!

 

[Foggy]

I would suspect that the wiring/ ground to that side of the coil packs harness
has some issue. There seems to be no/not enough 'fire' in that hole

 

[petethepug]

A leak down is still due. BT borescopes are inexpensive on Amazon. Verify visually the cylinder isn’t cracked and there’s no scoring on the cylinder walls from broken rings or contaminants.

Verify the harness, connectors & pins are in good nick.

 

[j91z28d1]

I would suspect that the wiring/ ground to that side of the coil packs harness
has some issue. There seems to be no/not enough 'fire' in that hole

I was thinking that it's gotta be firing some because of the carbon on the plug but maybe it's weak.

if you can back probe the pos and neg coil wires while running. and compare to others, it might give you an idea if you have weak power to that coil.


other than that. I'm not sure what a leak down test will show you that a compression test didnt. is the engine tapping at all. still have afm on it? someone here had a lifter that was fine turning cranking and for a few secs if running but then collapsed and missed. it was a faulty afm lifter, even thou I believe it was turned off in the tune. it was still releasing somehow.

 

[rdezs]

That slop in the rocker arm you referred to.... I assume you mean you can move it left and right across the top of the valve stem, and you're not referring to free play up and down?

 

[Keiterburb]

That slop in the rocker arm you referred to.... I assume you mean you can move it left and right across the top of the valve stem, and you're not referring to free play up and down?

Correct no movement on any rocker up down off push rod, just side to side and every one has that when not on compression. No loose or stuck lifters and #5 not a AFM/DOD lifter

 

[Keiterburb]

I was thinking that it's gotta be firing some because of the carbon on the plug but maybe it's weak.

if you can back probe the pos and neg coil wires while running. and compare to others, it might give you an idea if you have weak power to that coil.


other than that. I'm not sure what a leak down test will show you that a compression test didnt. is the engine tapping at all. still have afm on it? someone here had a lifter that was fine turning cranking and for a few secs if running but then collapsed and missed. it was a faulty afm lifter, even thou I believe it was turned off in the tune. it was still releasing somehow.

No engine noise very smooth sounding

 

[rdezs]

I suppose you could have broken the lower oil control ring on piston number five. Compression would still be good, especially with extra oil coming up around the rings. And that oil would foul the spark plug, noticeable at idle. But then again you swapped spark plugs and that had the same immediate effect? If so, follow up on the above advice checking wiring to that coil.
If the misfire at idle was due to a lifter hanging up I would expect you to hear ticking sounds. Live data from a bidirectional scanner while the engine is running would be very useful. That would narrow it down real quick between an injector or coil signal.

 

[rdezs]

In the absence of such a scanner.... Have you tried swapping injectors yet?

 

[Doubeleive]

In the absence of such a scanner.... Have you tried swapping injectors yet?

"Replaced all 8 fuel injectors with stock GM replacement from rock auto"

 

[Doubeleive]

I would suspect that the wiring/ ground to that side of the coil packs harness
has some issue. There seems to be no/not enough 'fire' in that hole

I agree with foggy you probably need to move on to the electrical side, start by ohm testing the harness coil/injector HARNESS and go from there

 

[rdezs]

I think you pretty much narrowed it down then. Wiring harness issue to number five coil, or you've lost your oil control ring on piston number five. So yeah, I think you'll need live data to confirm the coil firing normally or abnormally. That's the more likely issue. You don't want to drive it too long with the misfire. Or you'll be looking at a catalytic converter issue next.

 

[Dustin Jackson]

Some good advice in here. I think I comment on your Facebook post but I’m curious on the cam lobes for that cylinder. The LS lifters can fail in different ways even when not AFM lifters. The tray that holds them in position is plastic and the lifters can spin in the tray and damage the cam lobe and wear it down resulting in poor ignition conditions

If it comes down to it you should be able to peak down the valley cover at the cam but let’s start with the basics before opening the motor. I think you’ve tested the spark, compression, and fuel not sure what’s left to check before you dig in

 

[Keiterburb]

Just looked over wiring and checked for power and ground to the main coil pack disconnect, had both there with key on engine off. Shot for continuity from coil #5 connector back to main coil pack connector and all wires were solid there. Also 12V was solid at first injector connector. I did find some wire bundle with wear indication way down under power steering reservoir also looks like it was misrouted during someone’s previous service work.

 

[Dustin Jackson]

@Keiterburb Mine is routed through the power steering lines like that also I saw a couple weekends ago. Not sure if that’s from factory or not

 

[Keiterburb]

Cylinder #5 TDC leak down test only 4% leak rate out rings, could hear only through the oil cap. So other than a borescope in the hole I think I may be down to having to pull everything back off including valley cover to see if I can inspect the Cam lobe for wear?

 

[rdezs]

At this point, I think I'd be pulling the heads and the lifters. It would be a great time to do the AFM delete.... with the inherent problems of AFM, it just seems sacrilege to reassemble AFM components

 

[Doubeleive]

I would do a noid light test before tearing the engine apart.

 

[j91z28d1]

for me pulling it apart and not finding anything mechanical wrong would be a last resort. but yeah, a afm delete would at least make it worth while.

when I said check for power, I'd use back probe pins, at the individual connectors on the coils. these are lole 5$ on Amazon and hope there's a lower voltage on #5. you can follow the wires thru the seal and to the pin inside without damaging anything.

you probably don't have it handy, but I'd pull out my pocket scope next and check the trigger wire at the coil from the ecm. but these days mechanical work is the last thing I like to do. if your multi meter does hz. it might tell you something, but not sure.


byond that I'm out of ideas.. back to basics. have you looked at the fuel trims and miss fire counts? when it's missing on a gm the miss fire number will constantly count up while it's missing. that and something as simple as a loose spark plug will miss.

 

[j91z28d1]

I would do a noid light test before tearing the engine apart.

Yes, can you still rent those at auto parts stores?