Motor cranks most of the time

Tiny
ERICTYLER180
  • MEMBER
  • 2001 GMC
  • 8.1L
  • V8
  • 2WD
  • AUTOMATIC
  • 160,000 MILES
Motor cranks most of the time and I replaced the fuel pump and filter but the check engine light wont stay on long enough to throw a code to tell me what it is sometimes I have to turn the lights and all electronics off for truck to start its a 2001 GMC Sierra 2500 HD with a 8.1l vortec
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Tuesday, June 10th, 2014 AT 6:53 AM

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Tiny
WRENCHTECH
  • EXPERT
The computer stores codes in memory. The codes will be there is the battery hasn't been disconnected.
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Tuesday, June 10th, 2014 AT 8:48 AM
Tiny
ERICTYLER180
  • MEMBER
Battery hasn't been disconnected what else would it be if isn't throwing a code
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Wednesday, June 11th, 2014 AT 3:00 PM
Tiny
WRENCHTECH
  • EXPERT
If the check engine light has come on at all while the truck was running, then there will be a code stored.

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.

4) If all of these things check good, then you would need to do a complete compression test.

Once you have determined which of these functions has dropped out,
you will know which system is having the problem.
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Wednesday, June 11th, 2014 AT 3:05 PM

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