2013 GMC Yukon Denali 6.2L random misfire

[cjsmith718]

Hey all.

I have a 2013 Yukon XL Denali with about 120K miles on it. I have it serviced about every 4-5k miles or so.

Basically one day it felt like there was a misfire and before long check engine light came on. The cheaper code readers would say misfire in cylinder 3 but the fancier code readers would read random misfire & misfire on cylinder 3.

Here is what I have done so far.

I have replaced all plugs, wires & coil packs and issue persists. Fuel injectors have also been replaced. By the way, I didn't just replace for the sake of it without some diagnosing before hand.

I would still get the same error codes.

I have taken it to 2 mechanics and they don't know what to make of it. They did some fuel pressure tests and they said pressure looks great. They can't see a vacuum leak either.

Finally, when testing for a spark we found that a signal isn't always being sent down the wire to the plug to fire. Maybe one in every 5 fires on each plug was skipped. For the sake of me trying to explain this better imagine 1 plug firing like this *** fire - fire - fire - skipped - fire - fire - fire - fire - fire -skipped - fire - fire - fire *** and so on. This would do it on all plugs.

Any ideas would be great because I am close to giving up on this.

Thanks everyone!

 

[Doubeleive]

well if you are going to throw money at it I would look at the injector wire harness, or wiggle it, jiggle it, doing a continuity test on it, throw scope on it, etc, etc.

 

[cjsmith718]

Forgive me ignorance here, not trying to question your advice, just looking to better understand myself but would the injector wire harness be a culprit of a signal not being sent down the spark plug wires?

 

[B-train]

Does the misfire go away once off idle when using whatever you used to check it? Have you tried running in 5th gear and see how it reacts? The reason for this is I'm wondering of it is AFM related possibly

 

[swathdiver]

These motors are sequential fuel injection.

To the OP, get serious and start following the troubleshooting guide in the shop manual (AllDataDIY). As you can see, the parts cannon is expensive and a waste of time.

If you brought the car to me after having done all that other stuff, I would run a compression test after having a look with my Tech-2 on all system and possibly performing a Crankshaft Position Variation Learn.

I might stick a bore scope down the plug hole to look at the piston and pull the valve cover to check the valve and related parts.

 

[cjsmith718]

Does the misfire go away once off idle when using whatever you used to check it? Have you tried running in 5th gear and see how it reacts? The reason for this is I'm wondering of it is AFM related possibly

I will give it a shot this evening and I'll let you know the results. I appreciate your input.

These motors are sequential fuel injection.

To the OP, get serious and start following the troubleshooting guide in the shop manual (AllDataDIY). As you can see, the parts cannon is expensive and a waste of time.

If you brought the car to me after having done all that other stuff, I would run a compression test after having a look with my Tech-2 on all system and possibly performing a Crankshaft Position Variation Learn.

I might stick a bore scope down the plug hole to look at the piston and pull the valve cover to check the valve and related parts.

This 'parts cannon' you speak of I felt was necessary because at 120K miles I don't believe that the previous owner had ever changed the plugs, wires etc.

 

[Doubeleive]

Forgive me ignorance here, not trying to question your advice, just looking to better understand myself but would the injector wire harness be a culprit of a signal not being sent down the spark plug wires?

that is how the injectors get power and ground and on/off signal is thru the wiring harness, but I would not just go out replace it. I am not sure but I think others have mentioned that #3 is a afm lifter so if that has not been ruled out already then it's probably more logical to start looking internally

 

[swathdiver]

I will give it a shot this evening and I'll let you know the results. I appreciate your input.


This 'parts cannon' you speak of I felt was necessary because at 120K miles I don't believe that the previous owner had ever changed the plugs, wires etc.

Plugs and wires are maintenance, the injectors and ignition coils are what I was referring to. Where are you at today with this?

 

[cjsmith718]

that is how the injectors get power and ground and on/off signal is thru the wiring harness, but I would not just go out replace it. I am not sure but I think others have mentioned that #3 is a afm lifter so if that has not been ruled out already then it's probably more logical to start looking internally

Ah ok this makes sense. I'll start looking into getting it tested.

Plugs and wires are maintenance, the injectors and ignition coils are what I was referring to. Where are you at today with this?

Injectors were replaced by a shop, I did the plugs, wires & ignition coils. When replacing plugs & looked at ignition coils and they didn't look great so this is why I replaced them while I had things mildly taken apart.

Still same state as my original post. However since the post I have found a small oil leak from somewhere. Lots of oil built up over time on the back of the engine but I can't seem to find the oil leak itself. It isn't big enough to leave oil on the ground where the car sits but the oil pressure gage is low too.

 

[B-train]

I have the same problem (08 Denali) . I replaced oil pan gasket and the oil pressure sensor.....still had a leak. Try and look down from the top with a good mirror and high-powered flash light. If you don't see oil running down the valley to the heads, it's probably a rear main seal.

I don't feel like a whole Saturday on a lift is worth my time since 1 quart of leakage/usage in 5k is pretty cheap in oil money. I usually never have to top off before an oil change. Card board where it parks is good enough.

Eventually I'll probably pull the Trans and do the fix, but I know after thousands of miles of continuous running that it isn't a dire problem and just keep eye on it.

Honestly, it seems as though the on/off thing makes it seem worse. Just did 3200 miles in 5 days and didn't use a drop of oil. But, if it sits after a daily trip for weeks, I'll lose just a little to the rear main seal.

For what that's worth...