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2002 silverado with a p0300 code and out of ideas?

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by cowboy2586, Nov 11, 2011.

  1. cowboy2586

    cowboy2586 New Member

    Hey, new to site. i have a 2002 silverado with a 4.8l 2wd. a few weeks ago, it started running really rough, so i put my scan tool on it, had several codes. knock sensor circuit 2, random misfires. and a few i can't remember. started with wires, plugs, seafoam in the fuel tank, and it helped, but not fixed. kept reading through the forums here, and got led towards knock sensor. replaced both, and rtv'd the plugs to prevent future corrosion and replaced intake gasket. that took care of the knock sensor code. but still running like crap. changed fuel filter. have between 160 and 175psi of compression on all. fuel pressure is holding between 50 and 55psi. checked individual coils and all are firing. it really feels like the timing is being retarded by the ecm. if the misfire code is cleared prior to starting, the engine fires without hesitation and it is smooth, for a few seconds. the longer it runs (which is not but maybe 30 sec to a minute) it gets worse and worse and worse, like the ecm is trying to correct the misfires incorrectly. have checked the MAP sensor, fuel pressure regulator, fuel injectors are spraying evenly on both rails. there is not an intake leak any where. no cat codes are present. or o2 sensor codes. does anyone know of anything else that would cause the ecm to falsely adjust timing or a next possible step?? i'm staring at a brick wall with this thing..
  2. TRPLXL2

    TRPLXL2 New Member Platinum Contributor 1000 Posts

    Welcome to the club!On my s10 the ecm retarded the engine -4 degrees, and I read in my helms book that it should be 0 so I did a crank relearn on it and it made the truck run better although I didn't have any codes like you do, a bidirectional scanner would help you out a lot.
  3. cowboy2586

    cowboy2586 New Member

    Thanks for the info. How do I do a crank relearn?
  4. WARLOCK

    WARLOCK New Member

    What do you have for a scanner. If youhave a good one it will tell you about crank relearn.
  5. TRPLXL2

    TRPLXL2 New Member Platinum Contributor 1000 Posts

    I have a Snap on MT2500 scanner updated to 2008, on several vehicles it walks you through the crank relearn. You gotta have the certain tools to do it, tools make the mechanic in some cases. New cars suck lol!!!

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