Originally Posted by hgrimm
Hello, I love my GMC 2500 4x4 but have been having issues over the last 2 months. It first started missing (engine light flashing) when I hit a bump in the road. Five times the trouble started when I passed a bridge on paved roads. **Gotta be a ground..!! That eventually turned into a hard start much like a loose battery cable. After much reading on the internet and 4 visits to mechanic shops who applied 3 different scanners, the truck finally died on the road today.
It won't start and more or less just weakly turns the starter very slowly and sporadically. Prior fixes included: Plugs and wires changed, fixed a vacuum leak, checked for intake leaks (none), cleaned the MAF sensor and scanned the O2 sensors (one is weak). Tightened and cleaned all battery cables and the ground was checked. Battery is strong and battery ends are good. Did the tug test on throttle body sensor and pedal sensor. Does not indicate symptoms of the fuel filter or the cat. converter. Scanners gave the P0300 (Random misfire) each time. Not all on one bank. Mileage is 220,000 and fuel pump was changed probably 80,000 miles ago.
More reading leads me to suspect the computer ground itself (under the battery). I understand there are more body grounds on the rear of the engine. It may be the computer itself. Any ideas appreciated...and thank you.
I suspect the misfiring and weak starting are unrelated.
Have you checked the battery voltage while off and while running?
Hard to do when she won't start, but did you prior?
Should be 12-13 volts off and 14-15 running.
That'd rule out battery and/or alt, which leaves starter.
Concerning the misfire, maybe a plug is bad?
Wire not connected firmly?
No doubt you've checked that already.
Bad coil on that cylinder maybe?
Hope you get her figured out bud.