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

[basstracker89]

Try riding with her

 

[prestige30165]

Well here we are again. I drove the truck and no issues. My wife then went up the road 2 miles to the Circle K and comes back to tell me the truck did the same thing as before. Jerking, RPMs running up and down and acting like it would die.

I put my scanner on it and NOTHING. No DTCs, warning lights and no check engine. I then drove it the same route she took and then went further up the road. Starts and stops, various speeds and turns but the truck was normal so I came back home. I attached my scanner and the only thing I can find at all is under the fuel system it shows something called "Command Air Fuel Equivalence Ratio" the indicated value is in "red" and it's 1.0 .

I believe the ratio being 1.0 means it is good, It is reading the air fuel ratio at 14,7 which is what you want it to be

 

[testdepth]

I believe my latest problem with this truck is fixed. AFM switching problem between V8 and V4 at low speeds under 50mph. I installed an AFM disabler for V8 all of the time. We have been driving it and no more jerking, hesitation, shuddering acting like it will stall. Smooth riding V8 all the time.

 

[Eggmanmja01]

Damn. I don't think my F150 is any better, but I would have to sell it.

 

[testdepth]

My wife just drove this truck 40 miles to her dentist with the BOOST AFM disabler engaged and she had no problems at all with the engine. Constantly switching between 8cyl and 4cyl to save 1mpg. GM engineers really suck.

AFM disable for the fix!!

 

[basstracker89]

My wife just drove this truck 40 miles to her dentist with the BOOST AFM disabler engaged and she had no problems at all with the engine. Constantly switching between 8cyl and 4cyl to save 1mpg. GM engineers really suck.

AFM disable for the fix!!

Lets hope so!! They had that crap in the 80s. It wasn't any good then either

 

[testdepth]

My wife just returned from her trip to the dentist. 80 miles roundtrip with no problems in stop and go traffic and HWY.

AFM was AFU.

 

[Eggmanmja01]

I'm glad she didn't need a tow 😁

 

[basstracker89]

I'm glad she didn't need a tow 😁

$$$$$$$$$$$

 

[greg vess]

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!

Did you replace the pick up sock in the fuel tank. It's a little nylon sock that goes over the pickup in the fuel tank. I've had cars before or trash gets into the gas tank and accumulates around that fuel pick up sock and chokes the flow of gasoline off. It causes symptoms exactly like what you have explained. In a run for a while that trash gets around the sock and then it cuts off. After you let the truck set for a while it'll start back up but then after you let it run for a little bit it'll cut right back out. Usually a new pickup sock is offered with the new pump but if it wasn't then it could be your problem. If that is the problem you need to take the gas tank off or out and totally dump it out. Clean it out real good and then put the fuel pump back in with the new clean sock. These LS engines being fuel injected running extremely high pressure. Like 58 PSI believe if I'm remembering that correctly. Any kind of blockage in that fuel system is going to cause a problem with fuel delivery. It could be a falter fuel pressure regulator, a clogged rail or that fuel sock if the gas tank is full of crap.

I've also seen sensors that will act up like that as well when they get hot. As soon as the center cools down it'll work as normal but then when it heats back up it'll shut off again. Normally the mechanics can't diagnose that because they're testing it when the sensor is cool. The technician needs to test the system when everything is it operating temperature including all the sensors then he may be able to get an accurate reading. I'm not saying any of this is definitely the problem but I have running this before and these were two problems that caused a lot of frustration.