1320king

iTrader: (4)

So Ive had a post going on another forum and figured to bring it here as well. I have a Misfire that is driving me nuts trying to figure out.... Here is what is going on so far and my setup.

2007 Avalanche LTZ 169k:

Recently did the AFM delete because of a collapsed lifter (2,200 miles ago) here is what is new / changed:

Fully Rebuilt heads (seals, springs, retainers, valve job)
New GM lifters
New GM plugs
New GM wires
New complete GM gasket kit
New GM non AFM Cam
New GM oil pump
New NON-AFM valley cover
New pushrods
New timing set
New air filter
Reprogrammed ECU

Car drove perfect for over 2,000 miles after doing all this work and now this is happening.

What is happening:
Service stabilitrak and traction control light comes on then goes away and the CEL stays on. When you shut the truck off and read it with a scanner it comes up with CYL3 misfire. NOTE: It mostly happens when its cold or warming up.

What I have done so far:
Swapped coil pack from 3 to 1: Cyl 3 misfire still
Swapped plugs and wire from 3 to 1: Cyl 3 misfire Still
Swapped injectors from 3 to 1: Cyl 3 misfire still
Compression check on cyl 3: 135psi compression within 3 cranks. manual requires over 100 for 7 crank

1320king

iTrader: (4)

Edited first post to make it shorter

D1SCSS

iTrader: (3)

Have you checked for a vacuum leak on the intake manifold?

Atomic

iTrader: (42)

What do the other cylinders put out on the compression test? Most of the time that is best to compare cylinders to one another rather than the absolute value.

1320king

iTrader: (4)

I checked for vacuum leaks but I realized both times I checked was with the truck hot and it usually only happens when the truck is starting to warm up.

1320king

iTrader: (4)

Checked for vacuum leaks with the truck cold and it was fine. I sprayed carb clean all around the intake manifold and no noticeable change at all. Sprayed around the inake manifold, vacuum hoses and intake and it was all fine.

1320king

iTrader: (4)

Bump, Today it was cold and the thing was misfiring all over. I need to find somebody with a nice snap on scanner so I can monitor whats going on. I did notice on my scanner that the TPS was at 23% wile it was about 170 degrees. Not sure if thats normal. I also saw that it said OL-Fault in one freeze frame. Not sure what thats about either.

FFDP

iTrader: (2)

There is no IAC on the DBW throttle bodies so the TPS will always read when idling. Some engines are different but anywhere from high teens to low 20's on the TPS is pretty normal. The colder the engine is the higher the number could be because the blade is open further as the idle rpm is higher.

OL-Fault is some sort of failure on the o2 sensors. Possible a sensor is dying and failing to report back proper data. A scan tool that can log the sensors and fuel trims is key to figuring that out.

1320king

iTrader: (4)

Good point on the IAC, I forgot about that. I was running a live monitor on the truck and saw the OL and CL was fine and Fuel trims looked fine but the truck was missfiring on cyl3 about 3 counts every 10-20 seconds. It was not enough to trigger a CEL wile the vehicle was hot. But cold the vehicle was misfiring enough to throw a CEL. All other cylinders were fine.

IAt looked goo
Map looked good
oxygen sensors tested fine
The cats were within about 3-5 degrees from eachother

I am not sure how to monitor for ignition dropping out on this scanner I have.

Atomic

iTrader: (42)

Last time I had something like that ended up being a bent valve causing bad compression. A leak down test will tell you a lot about the mechanical health of the engine.