Why does my truck turn over, but not start intermittently

Tiny
SARMARWEEKS
  • MEMBER
  • 1998 GMC C1500
  • 120,000 MILES
I have a 1998 GMC 1500 that will not start at times, but does turn over. When it doesn't start, I disconnect the coil wire from the coil that goes to the distributer and then turn over the engine. I then reconnect the coil wire to the coil and the truck starts just fine. I have already replaced all the parts in the circuitry of the ignition including the computer and the trouble still occurs intermittently. What else could be the problem?
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Thursday, September 22nd, 2011 AT 6:26 PM

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Tiny
WRENCHTECH
  • EXPERT
All "crank, no start" conditions are approached in the same way. Every engine requires certain functions to be able to run. Some of these functions rely on specific components to work and some components are part of more than one function so it is important to see the whole picture to be able to conclude anything about what may have failed. Also, these functions can ONLY be tested during the failure. Any other time and they will simply test good because the problem isn't present at the moment.
If you approach this in any other way, you are merely guessing and that only serves to replace unnecessary parts and wastes money.

Every engine requires spark, fuel and compression to run. That's what we have to look for.

These are the basics that need to be tested and will give us the info required to isolate a cause.

1) Test for spark at the plug end of the wire using a spark tester. If none found, check for power supply on the + terminal of the coil with the key on.

2) Test for injector pulse using a small bulb called a noid light. If none found, check for power supply at one side of the injector with the key on.

3) Use a fuel pressure gauge to test for correct fuel pressure, also noticing if the pressure holds when key is shut off.

Once you have determined which of these functions has dropped out,
you will know which system is having the problem.
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Thursday, September 22nd, 2011 AT 6:54 PM
Tiny
CARTERDN
  • MEMBER
I've been battling the same thing for a year. What I ultimately found was the longer bolts I installed to secure my battery cables to the battery were too long and bottoming out. This caused a loose connection at the battery. It wasn't until I decided to remove the aftermarket performance ignition box that I discovered by removing the terminals sandwiched at the post that my cables fit sloppy after tightening. I doubt this is your problem, but it was causing the voltage to drop at the coil. Had I not held a spark plug to my lips while cranking the engine over I would have never known there was no spark.
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Wednesday, October 5th, 2011 AT 12:42 AM
Tiny
WRENCHTECH
  • EXPERT
If you need help with something, Please start a new question
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Wednesday, October 5th, 2011 AT 12:44 AM

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