Having problems with your 2002 GMC Sierra 2500HD ?
2002 gmc sierra 2500 HD 8.1 496 DTC P0300 The truck has a serious misfire from 1800 rpm up. If i try to powerbrake it, it acts as if i had a rev limiter on it and have it set to 2000rpm.under normal driving cond. truck drives fine, but if i try to go over half throttle it will misfire and hesitate. i have changed throttle position sensor, throttle body, checked for bad grounds, vaccum leaks, changed wires and plugs, checked fuel pressure 58psi, changed fuel filter. Any help would be greatly appr
Well i could make a joke about the magic multipurpose relay,but i dont think you would appreciate that one.now two things i would look at here ,firstly the crank sensor ,try a new one and if that doesnt work then it could be the ECU unit playing up ,because in the ECU is a chip that controls the firing order and spacing of the spark ,like 153624 .But again this sort of problem can be very difficult to locate ,If you can borrow an identical truck and swop bits over till you locate the problem all well and good .but if you do change the ECU with one from a scrapyard dont forget the chip in the key ,transponder as well or it will not start
You may want to check the fuel pressure regulator. Remove the vacume hose from the regulator and see if it is sucking fuel. I repaired one today with the 6.0l but it is the same concept. That vacume hose is filling the plenum with fuel and causing a po300 which is multiple cyl. misfire.
Repair Help & Product Troubleshooting for 2002 GMC Sierra 2500HD
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