Mass Air Flow Sensor

Tiny
EDESIDERIO
  • MEMBER
  • 2000 GMC YUKON
  • 4.8L
  • V8
  • 4WD
  • AUTOMATIC
  • 200,000 MILES
Vehicle starting to shut down while driving, first we thought it was the flue pump so we changed it out. Then we were told it was our secondary Air Injector Valve now we are told it's the Mass Air Flow Sensor. Once the vehicle shuts down, we give it about one minute and the vehicle cranks and starts going again. It's constantly doing that now.
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Monday, February 1st, 2016 AT 1:01 PM

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Tiny
WRENCHTECH
  • EXPERT
If it won't start for one minute, that is when you have to do your testing.

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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Monday, February 1st, 2016 AT 1:27 PM

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