Hey guys, not sure if this is the right section to post in but I need some help with my wife's 2007 Yukon denali xl. It has the 6.2 l92 engine in it with 235k miles on it. around 170k I replaced rod bearings, oil pump, timing chain, vvt actuator, vvt cam sprocket, vvt solenoid and various other basic tune up items. About 10k miles ago, I replaced the injectors, spark plugs and wires.
Recently a problem developed, where it keeps throwing a P0131 (cylinder 1 misfire) code and my wife complains about the smell of fuel in the cab. I pulled the plug and it is pitch black, the rest of the plugs look normal.
I have tried the following to remedy the problem:

new plug gapped at .044
swapped coil pack
swapped spark plug wire
swapped the injector
compression tested (225psi)
pulled valve cover and inspected everything
repaired plastic line on evap solenoid (it was cracked)

none of this has made a difference, the misfire stays on cylinder #1 and before anyone asks, driver side front cylinder.
the only other code I have is for the evap solenoid, I replaced it a year or so ago with a cheap one, it probably crapped out again.

anyone have any suggestions where else to look? I am thinking about diving into the wiring harness next to make sure there is nothing broken or frayed. if I do do that, does anyone happen to have a pcm pinout for my vehicle or a wiring diagram for it?

 

Check the wiring to that injector. Might have a break or fray in it that is grounding it and therefore injecting far more fuel.
Injectors work by grounding thru the ECM. A shorted ground wire would keep injecting fuel.

 

Carbon build-up may be burning off.

 

ill give that a try, do you happen to know what pin on the ecu that injector is? I figure I can ohm test the wire.

 

What is the deeper history on it? Should not have needed that many parts at 170k miles. Same with the reasoning of why the "tune up" parts @ 225k miles. Not doubting anything you did, but directive clues can usually be found that way.

Do a compression and leakdown test on all 8 holes to see what you have overall. Using either a Tech 2 or HP Tuners type interface, you can then do a cylinder balance test at idle, where you can drop out each cylinder one by one, and measure how much each is contributing. If that's the only fault code you are getting, it may not be electrical, since most of that is diagnosed for opens and shorts to power/ground. You could have a valve sticking open randomly for example. A leakdown test can tell more than a compression test. See if you can hear air escaping out of the intake or exhaust, make sure the valves are closed by either removing the rockers or rotating the engine appropriately. Carbon on a plug means combustion is happening weakly or only sometimes to where the plug can't get hot enough to burn it off. No combustion at all would leave a plug like new, and proper running will leave the plug tan.

 

The vehicle had a strange on and off knocking noise with lower than normal oil pressure. after removing the rod bearings, all looked to be in excellent condition except one or two may have been slightly questionable. I believe my knocking noise was a result of a failing oil pump. after that minor overhaul, there were no more abnormal knocking sounds coming from the engine besides the notorious piston slap on cold start and the oil pressure has been excellent. I cant recall now but I think I may have been getting a cel for something timing related too and went a head and replaced all timing components while I was in there. the vehicle has ran great for the past 55k miles. at 225k the engine had a noticeable stumble and figured it was time for injectors, pulled the old ones out and had them cleaned and tested, two of them failed the flow test so I decided to replace them all. due to carelessness, I had broken a spark plug wire and decided to replace them all along with the plugs.
ill plan to do a leak down test, just have to find some time. strangely though, anything higher then idle, the vehicle runs fine without any stumble. ill hook my hp tuners up to it and try the balance test but now I am wondering if all it needs is a couple spirited highway pulls because the misfire code is not coming back on anymore.

the only other codes the car has thrown consistently is p0449 and p0420. for the most part I have ignored these codes but since they turn on the cel and that turns off remote start, I have to fix them so that my wife stops complaining about it. if p0420 is anything more than just an o2 sensor, ill just turn it off in hptuners.