1997 Chevy Cheyenne engine turns over but truck won't start

PYLERS

MEMBER
1997 CHEVROLET CHEYENNE
V8
2WD
MANUAL
83,000 MILES

I have a '97 Chevy Cheyenne C3500 cab/chassis with 6.5 L turbo diesel. I recently tested the glow plugs because of a hard cold weather starting problem, and found that 5 of the eight needed to be replaced. I replaced the 5 gp and the truck started fine right afterwards. In fact it started fine later that day, and the next morning to go to work. However, on the way to work I noticed that the temp gauge showed the engine got to running temp fairly quickly. When I tried to start it after work the engine turned over fine, but all of the guages went screwy ( spinning around, etc.) And all of the dummy lights were glowing dim, and the glow plugs were turning off and on quickly. Checked the pcm with a code reader, and got no codes. Towed the truck home, and let it sit until the weekend. When I worked on it that weekend the code reader could not connect to the pcm, and it still would turn over, but the gp system would not turn on and the fuel pump/system would not turn on. Let it sit untlil the next day, and pulled all fuses to pcm ( to reset the computer). After an hour or so I turned the ignition to start and everything came back on, ie gp and fuel pump, and the truck started, but the engine seemed to be turning fast, but the rpm gauge read normal. Shut the truck off and tried it again, and had the same results as before, engine would turn over, but the gp and fuel system would not power up. I repeated this several times over the past month with the same results. My question is: Is this a bad computer or is it something I did while replacing the glow plugs, or possibly some entirely different issue?

1 Reply

JASONRAY

MECHANIC
213 POSTS

Since it all started when you replaced the glow plugs, I would first start there. Perhaps there's a short to ground in that circuit. Or even a bad ground. Electrical problems (shorts and bad connections) can cause all kinds of 'screwy' problems. I love your choice of words, by the way. Try unplugging the gp's and turn the key on. Does it still do it? Maybe one of the plugs you replaced is BAD and it's shorted directly to ground internally. OR, maybe one of the one's you DIDN'T replace is bad. Once you've ruled them all out, start with fuses and relays that control those systems. Possibly the same or they may be at least wired in together. If it comes and goes, I would initially suspect a bad connection somewhere.