06 with the 4.2L, engine has about 130,000 miles. The engine is a 2004.
I just read the misfire diagnosis thread but I don't have the same symptoms.
Truck starts and runs fine when cold. When hot, it has a slight misfire at idle, but it's weird. I'll slow down to a stop light and it will idle fine for 30-60 seconds before the misfire starts. Or it will be misfiring in park, I'll hit the throttle and it will run smooth for 30-60 seconds again.
What I've done so far;
-Replaced the plugs (worn autolite platinums were replaced with the OEM AC Delco 41-103s)
-Cleaned throttle body, which was gunked up
-Cleaned MAF sensor
-Short and long term fuel trim are within 5% of zero, so it doesn't seem like a vacuum leak
The only code I have consistently is a P0418 which is for the SAIS. Every so often I get P0300 as well.
It occurred to me today since the truck and ECU are 2006, and the engine is a 2004, if that could play into this as well. I know GM made a lot of changes to the 4.2L for 2006, but I'm not sure if that could cause this issue. Whoever replaced the engine used the 06 exhaust manifold, the SAIS solenoid and hoses are attached to it as they should be.
With the new plugs and cleaned TB the thing runs way better at all other times and seems to start better.
I just read the misfire diagnosis thread but I don't have the same symptoms.
Truck starts and runs fine when cold. When hot, it has a slight misfire at idle, but it's weird. I'll slow down to a stop light and it will idle fine for 30-60 seconds before the misfire starts. Or it will be misfiring in park, I'll hit the throttle and it will run smooth for 30-60 seconds again.
What I've done so far;
-Replaced the plugs (worn autolite platinums were replaced with the OEM AC Delco 41-103s)
-Cleaned throttle body, which was gunked up
-Cleaned MAF sensor
-Short and long term fuel trim are within 5% of zero, so it doesn't seem like a vacuum leak
The only code I have consistently is a P0418 which is for the SAIS. Every so often I get P0300 as well.
It occurred to me today since the truck and ECU are 2006, and the engine is a 2004, if that could play into this as well. I know GM made a lot of changes to the 4.2L for 2006, but I'm not sure if that could cause this issue. Whoever replaced the engine used the 06 exhaust manifold, the SAIS solenoid and hoses are attached to it as they should be.
With the new plugs and cleaned TB the thing runs way better at all other times and seems to start better.