New problem with this 2012 Yukon XL 1500 Denali 6.2L. I really hate this truck! GREMLIN is back

[testdepth]

I was checking the wiring on this truck and barely bumped the wires next to the coolant temperature sensor and the plastic end crumbled off the sensor. Not sure if this would cause any of my issues? Odd that GMC installed this next to the exhaust manifold but felt no need for a heat shield on this when they put heat shields everywhere else.

 

[Greybeard]

Maybe I wrote it up wrong, (or a little miscommunication) on the top of your gas pedal is another throttle position rvdt, this tells the ecu where to position your tps on the engine. You can check this by plugging in your scan tool, turn key on (engine not running) and slowly push your pedal down. I don’t think the ecu cares if this fails thus no codes will be set.There should be no erratic reading while doing this.

Also look at the blac/white wire going to the ecu from rear of engine block (ground wire). Put a meter lead on the ground and pierce the top of the wire with a needle and make sure it reads good. That ground completes the ecu.

 

[Greybeard]

Engine cooling temp sensor.

 

[testdepth]

I replaced the cooling temp sensor with a new one. I previously had a misfire for only cylinder 6 I figured I had a bad new coil so I replaced it with a new one and then:

Got in and started it up. Right away I can tell the engine is misfiring (stumbling), check engine came on flashing, stabilitrak came on and traction control came on. I let the engine run and on their own the check engine, stabilitrak and traction all went away. I had the truck running but I can tell the engine is still misfiring (engine stumble) RPM drop a little and back up. I used the scanner to look at the misfire counts while running. Scanner still shows cylinder 6 randomly misfiring and no other one.

No check engine light or other warnings. Scanner only DTC is now a P0300 code.

I'm going to let it cool off and swap coil 6 for 4 and see if the problem shifts to cylinder 4.

 

[testdepth]

Maybe I wrote it up wrong, (or a little miscommunication) on the top of your gas pedal is another throttle position rvdt, this tells the ecu where to position your tps on the engine. You can check this by plugging in your scan tool, turn key on (engine not running) and slowly push your pedal down. I don’t think the ecu cares if this fails thus no codes will be set.There should be no erratic reading while doing this.

Also look at the blac/white wire going to the ecu from rear of engine block (ground wire). Put a meter lead on the ground and pierce the top of the wire with a needle and make sure it reads good. That ground completes the ecu.

According to the scanner the throttle and gas pedal are tracking as they should.

I cannot find a black and white wire from the ECU to the back of the block on this 6.2L truck?

 

[Greybeard]

I replaced the cooling temp sensor with a new one. I previously had a misfire for only cylinder 6 I figured I had a bad new coil so I replaced it with a new one and then:

Got in and started it up. Right away I can tell the engine is misfiring (stumbling), check engine came on flashing, stabilitrak came on and traction control came on. I let the engine run and on their own the check engine, stabilitrak and traction all went away. I had the truck running but I can tell the engine is still misfiring (engine stumble) RPM drop a little and back up. I used the scanner to look at the misfire counts while running. Scanner still shows cylinder 6 randomly misfiring and no other one.

No check engine light or other warnings. Scanner only DTC is now a P0300 code.

I'm going to let it cool off and swap coil 6 for 4 and see if the problem shifts to cylinder 4.

Perfect if not coil, bad plug if it doesn’t follow. While it’s running bad you could check the crank sensor output.

If not black/white could be just black. If not rear of block look to the right fwd. it’s there.

 

[testdepth]

Just swapped the coils for 4 and 6 and the problem did not follow. Scanner still shows misfire cylinder 6. I ran a new scan and the only code is a P0300. No check engine, no stabilitrak, no traction or any other warning lights.

I installed brand new iridium plugs the same day I installed new coils. I guess its possible for one to be bad?

I checked the crank and cam sensors. Both are functioning normally.

 

[Greybeard]

It does happen, before I purchase a new one I would swap plugs also. Just to verify it’s bad. If not all the coils on that side have the same ground. I hope it’s the plug, check the power wires going to the ecu to that coil.

If the cam sensor, crank sensors are doing their jobs the ecu controls the firing. You could check the wire going to your coil pack for voltage (or simply hook the coil pack up and ground a spark plug to engine, if good that clears your e and coil….that leaves compression and valves (didn’t want to go there) that engine is a Afm.

 

[testdepth]

I went and bought one single iridium plug and changed out cyl 6 plug. For now the stumble and misfire is gone. No codes, lights or warnings. I have not driven it yet though. I'll start it in the morning and if all is well I'll drive it down the road.

I know a guy that's a GM mechanic for 30yrs. I went up to the dealer to see him about these issues. While there I saw a Camden County Sheriff's Tahoe sitting there with the engine torn down. I asked him about it and then he tells me the lifters spun in it and it's a common problem in the 5.3 engine. Then he shows me the damn plastic lifter holder trays and explains how the lifter will rotate and grind away at the camshaft lobes. The cam had 3 lobes that looked like they had a grinder put on them.

 

[fast306stang]

I went and bought one single iridium plug and changed out cyl 6 plug. For now the stumble and misfire is gone. No codes, lights or warnings. I have not driven it yet though. I'll start it in the morning and if all is well I'll drive it down the road.

I know a guy that's a GM mechanic for 30yrs. I went up to the dealer to see him about these issues. While there I saw a Camden County Sheriff's Tahoe sitting there with the engine torn down. I asked him about it and then he tells me the lifters spun in it and it's a common problem in the 5.3 engine. Then he shows me the damn plastic lifter holder trays and explains how the lifter will rotate and grind away at the camshaft lobes. The cam had 3 lobes that looked like they had a grinder put on them.

Hopefully that plug was bad from the factory/cracked from being dropped and now we've eliminated that as being the source of the problem!