2012 Yukon 1500 XL Denali 6.2L while driving truck shudders, rpms run up and down until engine dies. Update at #44

[testdepth]

2012 Yukon 1500 XL Denali 6.2L. Truck shudders, RPMs run up and down until engine dies.

I have been having issues with this truck for the last month or so. 170000 miles on it. First started with stalling and shutting off while driving and that's resolved (crank sensor). Then in park and at idle after about 10 minutes the engine would completely shut off (EVAP purge solenoid). Then while driving at 45 mph the truck would act like it was going to stall, jerk back and forth and RPMs would go up and down but not stall completely. I think this jerking is resolved now.

I have replaced the following and spoke to a guy that's been a mechanic on GMs at the local dealer for 30yrs.
New AC Delco fuel pump
New MAF sensor
New crank sensor
New negative battery cables and cleaned contacts to bare metal
New coil packs
New iridium plugs
New throttle body
New oil pressure sensor and filter
New EVAP purge solenoid
New EVAP canister

All of this is replaced and all relearn procedures that were needed are done. The GM mechanic looked for any updates to this truck's ECM and other sensors but there were none called out.

Now just an hour ago this happens: My wife drove to the store with no problem. She then got back in to come home and tried to start it. While parked the check engine comes on, Stabilitrak Disabled, Traction Control Disabled, Service Stabilitrak all come on and engine runs like its missing. She drove it home this way.

I put my scanner on it and it shows P0300 code. I brought up the misfire screen and shows cylinder 6 is misfiring. I just replaced all 8 coil packs so its possible one went bad.

I'm not sure why the stabilitrak and traction control would come on and then say to service them?

 

[Fless]

The Stabilitrak and traction control are disabled because of the misfire.

After your crank sensor was replaced, was a CASE relearn done? If not, have one done to rule it out.

 

[Doubeleive]

2012 Yukon 1500 XL Denali 6.2L. In park and started but get check engine, Stabilitrak Disabled, Traction Control Disabled, Service Stabilitrak

I have been having issues with this truck for the last month or so. 170000 miles on it. First started with stalling and shutting off while driving and that's resolved (crank sensor). Then in park and at idle after about 10 minutes the engine would completely shut off (EVAP purge solenoid). Then while driving at 45 mph the truck would act like it was going to stall, jerk back and forth and RPMs would go up and down but not stall completely. I think this jerking is resolved now.

I have replaced the following and spoke to a guy that's been a mechanic on GMs at the local dealer for 30yrs.
New AC Delco fuel pump
New MAF sensor
New crank sensor
New negative battery cables and cleaned contacts to bare metal
New coil packs
New iridium plugs
New throttle body
New oil pressure sensor and filter
New EVAP purge solenoid
New EVAP canister

All of this is replaced and all relearn procedures that were needed are done. The GM mechanic looked for any updates to this truck's ECM and other sensors but there were none called out.

Now just an hour ago this happens: My wife drove to the store with no problem. She then got back in to come home and tried to start it. While parked the check engine comes on, Stabilitrak Disabled, Traction Control Disabled, Service Stabilitrak all come on and engine runs like its missing. She drove it home this way.

I put my scanner on it and it shows P0300 code. I brought up the misfire screen and shows cylinder 6 is misfiring. I just replaced all 8 coil packs so its possible one went bad.

I'm not sure why the stabilitrak and traction control would come on and then say to service them?

put a scanner on it, view live data, see where the misfires are, whichever cylinders are misfiring start swapping plugs first see if the misfire follows the plug if not then swap wires, if nothing changes then swap coils and see if the misfire follows the coil, if not then check fuel pressure and monitor injectors. if all that checks out then check coil wire harness, then injector wire harness. if all that passes then you might be looking at lifters next.
just a matter of troubleshooting and elimination until you find the cause.
the original coils were probably fine unless determined otherwise, sounds like the shotgun was fired instead of pinpointing the issue.
p0300 could indicate more than just cylinder 6 and #6 could have just been the one that was bad enough to store in history, viewing live data while driving or revving it up will show all misfire counts.
***also if you get to the point of where it could be lifters do a backpressure test first, a clogged cat can cause problems

 

[Joseph Garcia]

Have you checked the main ground from the engine block to the fire wall? Also, have you checked the major ground on the frame below the driver's foot? If these connections are not clean and tight, all sorts of dash warnings will pop up.

 

[swathdiver]

Sounds like you need a scan tool that can communicate with all modules, Chassis, BCM, etc. If all you're getting is a generic misfire code, my guess is that you have a "U" code or two as well.

A bi-directional scan tool can also see data saved at the time of the DTC being set.

Do you have a Tech-2?

 

[testdepth]

Misfire is fixed it was a bad brand new iridium spark plug. I bought a new plug and the misfire is gone. I drove this truck yesterday for 40 minutes at different speeds, turns, stops and starts. No issues found. This morning I drove it again and no issues. My wife got in and drove 2 miles up the road and comes back to tell me again tis truck is jerking, RPMs up and down and acted like it wanted to stall. She came home and I immediately hooked my bidirectional scanner to it. No DTCs, no check engine or any other warnings. I then drove it trying to get it to fail. I went her same route and then drove further up the road but there were no problems. For me it was normal.

I hooked up my scanner: No codes, no check engine and no other warnings. The only thing I can find is under "Fuel System" It shows Command Air Fuel Ratio and it has a value of 1.0 shown in the color "red". If I look at that data while the engine is running it's a flat line and never moves no matter how much gas I give it. I have no idea if this is a problem?

This is a 6.2L GMC

 

[Doubeleive]

Misfire is fixed it was a bad brand new iridium spark plug. I bought a new plug and the misfire is gone. I drove this truck yesterday for 40 minutes at different speeds, turns, stops and starts. No issues found. This morning I drove it again and no issues. My wife got in and drove 2 miles up the road and comes back to tell me again tis truck is jerking, RPMs up and down and acted like it wanted to stall. She came home and I immediately hooked my bidirectional scanner to it. No DTCs, no check engine or any other warnings. I then drove it trying to get it to fail. I went her same route and then drove further up the road but there were no problems. For me it was normal.

I hooked up my scanner: No codes, no check engine and no other warnings. The only thing I can find is under "Fuel System" It shows Command Air Fuel Ratio and it has a value of 1.0 shown in the color "red". If I look at that data while the engine is running it's a flat line and never moves no matter how much gas I give it. I have no idea if this is a problem?

This is a 6.2L GMC

what does the maf read at idle and at say 3000rpm

 

[testdepth]

AC Delco MAF was brand new when I installed it a few days ago. After warming the engine to normal temp of 210:

MAF at idle 6.15 to 6.36
MAF at 3000rpm 25.92 to 26.02

My RPMs at idle in park, jump between 585 to 620

Under the fuel system "Command Air Fuel Ratio" appears stuck at 1.0. This truck has 170000 and we have owned it for 10yrs. The O2 sensors have never been changed.

 

[SpareParts]

I think that's something our vehicles do not have or do not report. I have an 07 and have that same reading. Mine runs fine though.

 

[swathdiver]

MAF at idle 6.15 to 6.36
MAF at 3000rpm 25.92 to 26.02

Under the fuel system "Command Air Fuel Ratio" appears stuck at 1.0.

All normal.

 

[testdepth]

I can't find any info on this problem or what could cause this?

 

[testdepth]

Could the transmission cause this problem but not throw a code?

 

[mikez71]

So no codes, sometimes the idle bounces 575-625 and truck might jerk some?

Is this jerking at light cruise? Like when the AFM V4 mode would be active?
That could be a transmission problem, but the first thing most people do, is disable the AFM.

Not sure what the idle bounce is about.. That's in park/neutral? Or in gear foot on brake?

 

[B-train]

The only sensor you didn't replace was the MAP sensor. I had a weird scenario when I received the wrong sensor for my 2008 and it would go into a reduced power mode with the same brake/suspension lights illuminated at a certain engine load. Replaced with genuine GM and it's been fine. Maybe worth a $60 try

 

[testdepth]

My AFM system.
My AFM generally only kicks in when I let off the gas pedal. I just test drove it in "D" and watched my display show it was in V8 mode while accelerating from stop all the way to 75mph. Never once shifted to V4. As long as I maintained gas pedal pressure it stayed at V8. While maintaining speed it stays in V8 all the time.

As soon as I let off the gas pedal it shifts to V4 and if I never touch the gas pedal it will stay at V4 until about 42mph and it will shift to V8 and drop to V4 again at 25mph and then back to V8. I drove it on the HWY in "D" and accelerated to 75mph and maintained speed with my foot and the engine stayed in V8. as long as I maintain speed the engine never shifted to V4. At 75mph when I let off the gas pedal completely the engine shifts to V4 and will stay there until either I press the gas pedal again or the engine speed drops to about 42mph and then it will shift back to V8.

At anytime I start to barely decelerate by slightly lifting my foot off the pedal the engine shifts from V8 to V4. Only on deceleration.

I thought this system was suppose to shut 4 cylinders off at steady HWY speeds to save on fuel economy?? At steady HWY speed this engine stays in V8.

 

[the 18th letter]

My AFM system.
My AFM generally only kicks in when I let off the gas pedal. I just test drove it in "D" and watched my display show it was in V8 mode while accelerating from stop all the way to 75mph. Never once shifted to V4. As long as I maintained gas pedal pressure it stayed at V8. While maintaining speed it stays in V8 all the time.

As soon as I let off the gas pedal it shifts to V4 and if I never touch the gas pedal it will stay at V4 until about 42mph and it will shift to V8 and drop to V4 again at 25mph and then back to V8. I drove it on the HWY in "D" and accelerated to 75mph and maintained speed with my foot and the engine stayed in V8. as long as I maintain speed the engine never shifted to V4. At 75mph when I let off the gas pedal completely the engine shifts to V4 and will stay there until either I press the gas pedal again or the engine speed drops to about 42mph and then it will shift back to V8.

At anytime I start to barely decelerate by slightly lifting my foot off the pedal the engine shifts from V8 to V4. Only on deceleration.

I thought this system was suppose to shut 4 cylinders off at steady HWY speeds to save on fuel economy?? At steady HWY speed this engine stays in V8.

Usually above 75mph AFM doesn’t operate.

 

[Doubeleive]

Misfire is fixed it was a bad brand new iridium spark plug. I bought a new plug and the misfire is gone. I drove this truck yesterday for 40 minutes at different speeds, turns, stops and starts. No issues found. This morning I drove it again and no issues. My wife got in and drove 2 miles up the road and comes back to tell me again tis truck is jerking, RPMs up and down and acted like it wanted to stall. She came home and I immediately hooked my bidirectional scanner to it. No DTCs, no check engine or any other warnings. I then drove it trying to get it to fail. I went her same route and then drove further up the road but there were no problems. For me it was normal.

I hooked up my scanner: No codes, no check engine and no other warnings. The only thing I can find is under "Fuel System" It shows Command Air Fuel Ratio and it has a value of 1.0 shown in the color "red". If I look at that data while the engine is running it's a flat line and never moves no matter how much gas I give it. I have no idea if this is a problem?

This is a 6.2L GMC

tough one, but I would maybe have the wife drive and you monitor the scanner, see what happens
her reported symptoms are typical of maf/throttle body issue, which in turn can cause the transmission to shift funky, but that doesn't mean that it is the problem
but I would try and monitor it more with the scanner until the aahaah moment happens

 

[swathdiver]

Could the transmission cause this problem but not throw a code?

What problem? I thought it was a bad plug?

 

[testdepth]

What problem? I thought it was a bad plug?

Plug problem is repaired. This truck jerks, hesitates, RPMs run up and down and acts like it wants to die. I'm thinking it's something to do with the AFM shifting back and forth from V8 to V4. I did not know these trucks are always shifting back and forth between V8 and V4, even at low speeds. I thought this system was designed for distance steady driving where it would shut off 4 cylinders to gain gas mileage. Mine isn't doing that. Mine will stay in V8 unless I let off the pedal and it will change to V4. Only on deceleration though.

 

[mikez71]

Part of the reason I was thinking AFM, a difference between how you drive vs. your wife.
You have to be really light on the throttle.. just barely cruising..

But since you have been testing when it goes into V4 mode, I suspect that's not really it.

You mentioned O2's, might want to pull those up on your scanner.
I would say something should show up SOMEWHERE while scanning parameters, sounds like it maybe intermittent.. but usually those will leave some code?

Your spark plugs... were they from amazon? Just because I've heard a couple stories..