Flashing check engine light. P0300-6F on 02 chevy 1500 4x4 4.8 gas engine

[hatzie]

Originally Posted by hrc200x

Working on a 02 chevy half ton 4x4 off and on for a couple months. 4.8 gas, has around 150,000 miles. Want to say it had new plugs and wires within the last 20,000 miles and intake gaskets replaced in the last 30,000. In May it had a solid check engine light with code P0300-BB engine misfire detected, P0172-29 fuel trim system rich bank 1 and P0175-29 fuel trim system rich bank 2. It showed misfires on cylinder 3 and 4 with the most being on 4. I put the coil from cylinder 2 on 4 and the plug and wire from 4 in 2 and the misfire stayed at cylinder 4. Looking at the plugs, number 4 is definitely rich. Volts on the 02 sensor bank 1 sensor 1 seemed a little different than the rest so I was going to try a new 02 sensor on the driver side before the cat. sensor was rusted in so I wasn't able to get it loose till a few days ago. I installed a new bosch 02 sensor, cleared codes and now have a flashing check engine light with code P0300-6F engine misfire detected. There are still misfires on 3 and 4, if I increase the rpm number 4 misfires increases while 3 seems to stop misfiring. The truck doesn't get driven on the street, just moved around the property with tools in it. I took videos of the scanner screen because I'm not sure what is correct or incorrect numbers in them. Not sure the videos would upload because of the size.

It's worth running a compression check on all 8 cylinders and noting how far out three and four are to rule out mechanical problems.

If you don't have low compression on those cylinders relative to the other six then check the injectors aren't leaking or spraying very badly. If you have a couple bad injectors I'd get some used GM injectors from a U-Pull-It. New injectors are too expensive for a yard truck or not worth buying... there's nothing in between.