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

[Greybeard]

Ok, plug it in and set up to view your ign systems and voltage. Drive it and hope for it to act up. When it does, and if voltage drops or/and ign coils cut out you know that you could have some bad grounds or a loose wire somewhere. If everything looks good at that point you know you have a fuel problem.

You should be able to pull up crank, cam sensors and look for deviation in them if not suspect wiring. Same for throttle position sensor if ok look for wiring. Wheel sensors and wiring also.

I hate to flog a dead horse, but I think you have a bad ground going to the ecm or ign system/switch.

 

[voodoochild1989]

I'm still having problems with this Yukon Denali 6.2L.

This morning after sitting all night my wife goes to an appointment. After normal cold start she started down the road at 45 mph and gets 5 miles from the house when the truck while running down the road starts chugging/choking back and forth and RPMs are going up and down. Truck felt like it would stall but didn't. She drove it back home and parked it. Truck did not have an engine code or code for anything. After warm up and engine at normal temp I used my TOPDON code reader to find no codes or check engine. I then took it to a dealership mechanic that has worked on GMs for 30yrs. He ran his reader and no codes or check engine. He did the relearn on the crank sensor again. He also checked for any updates to the ECM but there were none. Right now the RPMs cutout at 3500 and it's supposed to be 4000. I did it a few times by slowly pressing the foot pedal and watching the RPM climb. Once it gets to about 3500 it automatically reduces back to idle of 600 rpm. Truck is not reliable as is. Any ideas?

In the last few weeks I have replaced the following parts with new:
OEM AC Delco fuel pump
Negative battery cable
AC Delco MAF sensor
Crank sensor (did the relearn using my scanner and the dealer scanner)
Throttle body
Plugs and coil packs
Valve cover gaskets
EVAP Purge Solenoid
EVAP cannister

Help!

Had something similar happen on a 2014 Chevy Silverado about 7 or 8 years ago. Just bought it used and the second day or so it started reving up and braking on its own, all gauges going up and down on the dash, locks going up and down, etc. Took it back to the dealer and they couldn't find anything wrong. Did some research and found out that this was a fairly common issue for that year but no recalls. I ended up getting a Toyota Tundra and never looked at another GM truck again.

 

[voodoochild1989]

Hope you can figure this one out man

 

[testdepth]

Ok, plug it in and set up to view your ign systems and voltage. Drive it and hope for it to act up. When it does, and if voltage drops or/and ign coils cut out you know that you could have some bad grounds or a loose wire somewhere. If everything looks good at that point you know you have a fuel problem.

You should be able to pull up crank, cam sensors and look for deviation in them if not suspect wiring. Same for throttle position sensor if ok look for wiring. Wheel sensors and wiring also.

I hate to flog a dead horse, but I think you have a bad ground going to the ecm or ign system/switch.

Does it matter what type of wire you use for the ground strap? The one attached above the master cylinder and the head is a strap ground unlike the battery negative cable ground. I assume the strap one is used because the motor is moving and it flexes with the engine.

 

[Greybeard]

No not really, size matters (so I’ve been told) the more amps it carries the thicker or heavier it needs to be. You need to look on the right side engine front and back most ecu ground are there. Look for black wires with white strips or just black those are equipment (sensor) grounds. There should be two on the back of block one heavy one thin. Put a meter on them.

 

[Greybeard]

Just for sh@t and grins, just Incase your ecu does not pick it up….setyour scaner up and look at your throttle position sensor. Slowly push the pedal down and make sure the reading increases and decreases with pedal movement. I would think it was checked but just in case.

 

[testdepth]

Just for sh@t and grins, just Incase your ecu does not pick it up….setyour scaner up and look at your throttle position sensor. Slowly push the pedal down and make sure the reading increases and decreases with pedal movement. I would think it was checked but just in case.

Yes I already checked the throttle position and verified its movement. I'm waiting for new ground wires to get here today and I'll replace them. I did find a good video for a 5.3 motor and it's ground locations but not sure if it's the same for 6.2.

 

[testdepth]

https://charm.li/GMC/2012/Yukon%20XL%20Denali%202WD%20V8-6.2L/Repair%20and%20Diagnosis/Locations/Ground%20Locations/Master%20Grounds%20List/

 

[fast306stang]

I would swap that coil pack with another one and see if the problem follows that cylinder. Also I'm not familiar with your coil pack type, but my friend had an early 2000's Corvette and pinched the ground wire on one of his coil packs when he upgraded, that caused him to chase his tail on an intermittent problem until he found it

 

[testdepth]

One other note about ground wires on this truck. We are the second owner and this truck has spent its life in South East GA. None of the grounds or wires on this truck show any corrosion or rust and there is no rust under this truck. I went ahead and cleaned the grounds I can find anyway.