Tweet
I've tried posting on some of the Chevy/GMC forums but have come up empty so far.
Slightly long read...
I have a 2008 Sierra CC 2WD with a J-code 5.3L LY5 with the wonderful active fuel management system. Truck has 344k miles on it.
On Friday, I drove roughly a 160 mile round trip to a job and all was well. Come Saturday i get about 5 miles from the house and I get the Service Traction/Stabilitrak and engine lights flashing on the dash. I get rough idle around 580-630RPM. The truck is sluggish until it gets up to speed and then drives fairly normal aside from the annoying dinging and flashing lights every few minutes.
I use a handheld scanner(Snap-on/Matco, I don't remember which) and at first it has a P0300 - random multi-misfire. I clear that code and restart the truck. After about a minute it throws P0306 for #6 misfire. Same flashing lights and the engine light goes from solid to flashing every few minutes. Sunday, I finally get a chance to start checking forums and get my list of things to look for.
Based on other similar cases found online, so far I have:
Replaced the plugs and wires(which were close enough to the change interval)
Swapped the coil with #2
Swapped injectors with #2
Ran some Injector cleaner through it
Checked all wiring for damage
Pulled the valve cover and checked the springs, rockers, and push rods. -Everything looks brand new under the valve cover(no sludge or buildup)
None of the above changed the symptom or checked bad.
Ran a compression Test - At first it did not read any compression and #2/#4 read 160psi. I applied air(~50psi) to the cylinder to see if a valve was hung open or if there was blow-by in the crankcase. This seemed to make a difference because afterwards it read 160psi just like #2/#4. This has me thinking it is a sticking valve or lifter problem. After the compression/air testing the truck idled normally for about 7-8 minutes before giving me my p0306 and flashing lights back. And after driving it and checking again I still have good compression on #6.
To add to the fun, driving back from the Chevy house to my shop and then again to my house - the warning lights and symptoms would come and go(and by go I mean a completely clear dash and normal idle). This intermittent nature has me thinking even more that it is something sticking on a valve or lifter.
From all of my reading on this forum and others, it appears to be one of two things - either the AFM lifters or the AFM solenoid(s). Speaking with my friend at the Chevy house, he said he rarely sells the solenoids/plate kit but frequently sells the lifter sets. However he said normally the lifter sets are for lifters that have turned and started eating the cam.
I have access to a Tech2 to do some further troubleshooting, but haven't had a chance to stop by and use it.
My Questions:
How many out there have had the AFM solenoids replaced and it resolved the misfire problem?
Can a Tech2 activate/deactivate the AFM solenoids while running?
Will a Tech2 give me data to the specific solenoid for #6?
Can a Tech2 permanently disable AFM?
I'm really not wanting to pull the heads to swap lifters(because of the high mileage).... At that point, I would look for a new long block or low mileage 5.3 to swap in.
The fucked up thing is, I've driven about 800 miles on 7 cylinders and it's getting slightly better mileage than it was before! (of course that could be the plugs and cleaners helping it out)
Any help or assistance is greatly appreciated.
Slightly long read...
I have a 2008 Sierra CC 2WD with a J-code 5.3L LY5 with the wonderful active fuel management system. Truck has 344k miles on it.
On Friday, I drove roughly a 160 mile round trip to a job and all was well. Come Saturday i get about 5 miles from the house and I get the Service Traction/Stabilitrak and engine lights flashing on the dash. I get rough idle around 580-630RPM. The truck is sluggish until it gets up to speed and then drives fairly normal aside from the annoying dinging and flashing lights every few minutes.
I use a handheld scanner(Snap-on/Matco, I don't remember which) and at first it has a P0300 - random multi-misfire. I clear that code and restart the truck. After about a minute it throws P0306 for #6 misfire. Same flashing lights and the engine light goes from solid to flashing every few minutes. Sunday, I finally get a chance to start checking forums and get my list of things to look for.
Based on other similar cases found online, so far I have:
Replaced the plugs and wires(which were close enough to the change interval)
Swapped the coil with #2
Swapped injectors with #2
Ran some Injector cleaner through it
Checked all wiring for damage
Pulled the valve cover and checked the springs, rockers, and push rods. -Everything looks brand new under the valve cover(no sludge or buildup)
None of the above changed the symptom or checked bad.
Ran a compression Test - At first it did not read any compression and #2/#4 read 160psi. I applied air(~50psi) to the cylinder to see if a valve was hung open or if there was blow-by in the crankcase. This seemed to make a difference because afterwards it read 160psi just like #2/#4. This has me thinking it is a sticking valve or lifter problem. After the compression/air testing the truck idled normally for about 7-8 minutes before giving me my p0306 and flashing lights back. And after driving it and checking again I still have good compression on #6.
To add to the fun, driving back from the Chevy house to my shop and then again to my house - the warning lights and symptoms would come and go(and by go I mean a completely clear dash and normal idle). This intermittent nature has me thinking even more that it is something sticking on a valve or lifter.
From all of my reading on this forum and others, it appears to be one of two things - either the AFM lifters or the AFM solenoid(s). Speaking with my friend at the Chevy house, he said he rarely sells the solenoids/plate kit but frequently sells the lifter sets. However he said normally the lifter sets are for lifters that have turned and started eating the cam.
I have access to a Tech2 to do some further troubleshooting, but haven't had a chance to stop by and use it.
My Questions:
How many out there have had the AFM solenoids replaced and it resolved the misfire problem?
Can a Tech2 activate/deactivate the AFM solenoids while running?
Will a Tech2 give me data to the specific solenoid for #6?
Can a Tech2 permanently disable AFM?
I'm really not wanting to pull the heads to swap lifters(because of the high mileage).... At that point, I would look for a new long block or low mileage 5.3 to swap in.
The fucked up thing is, I've driven about 800 miles on 7 cylinders and it's getting slightly better mileage than it was before! (of course that could be the plugs and cleaners helping it out)
Any help or assistance is greatly appreciated.
Comment