Crank shaft sensor? How to test to see if its good or not

Tiny
1CAPTAIN
  • MEMBER
  • 2005 CHEVROLET IMPALA
My car runs great as long as it does not get hot. When it does it shuts down and will start and instantly shut down. Will run again after it cools off. Changed the fuel pump and temp sensor. Next what to try?
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Saturday, August 27th, 2011 AT 3:32 PM

12 Replies

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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Saturday, August 27th, 2011 AT 3:57 PM
Tiny
JDL
  • EXPERT
When the problem occurs, have a helper crank it, while you check for spark at the plugs. You can carry a spark tester in the glove box, it won't get hot. If it is hot under the hood, use gloves, pull off a spark plug wire, stick tester in boot, ground metal part of tester to metal part of engine, watch for spark.

What is litre size of engine? I looked at 3.4L, you have two crank sensors. One puts out an ac pulse signal and wiring goes to ignition module. The other is a hall switch, puts out a dc pulse goes to the pcm.

Any applicable trouble codes?
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Saturday, August 27th, 2011 AT 4:03 PM
Tiny
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It starts when its cold. And runs until it get hot and then shuts down. Then until it cools down it will start but not stay running. Sounds like crap for the few seconds it does run we did manage to pull a code last night while it was running briefly after shutting down. It was a P0300. We have not check engine lights on or anything like that.
Now today it will start after sitting all night. Warm up and poof shut down.
Its frustrating thinking a stick of dynamite might be the fix to it.
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Saturday, August 27th, 2011 AT 4:45 PM
Tiny
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It is a 3.8
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Saturday, August 27th, 2011 AT 4:46 PM
Tiny
WRENCHTECH
  • EXPERT
If you perform the testing I requested we can isolate whether the crank sensor is working but it has to be done while it's not starting.
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Saturday, August 27th, 2011 AT 4:48 PM
Tiny
1CAPTAIN
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Ok what do I need to do to test the crank sensor?
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Saturday, August 27th, 2011 AT 4:49 PM
Tiny
1CAPTAIN
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Sorry did not read far enough. Fuel pressure tested ok. Will check spark. But why would it stay running for approx 10 minutes until it gets hot and then shut down.
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Saturday, August 27th, 2011 AT 4:54 PM
Tiny
JDL
  • EXPERT
I agree with wrenchtech, check the basics.
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Saturday, August 27th, 2011 AT 5:02 PM
Tiny
WRENCHTECH
  • EXPERT
Sure, you can go buy a lab scope and test your Crank Sensor which won't help unless you're doing it when it's dead or you can do the easier tests and we can find out through process of elimination.
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Saturday, August 27th, 2011 AT 5:08 PM
Tiny
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Ok have checked and it has spark. Will start right now also not sure how long it will run that's anyones guess.
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Saturday, August 27th, 2011 AT 6:31 PM
Tiny
1CAPTAIN
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A friend that is a mechanic stopped by and tried several things and ended up unplugging the mass air flow sensor and it started right back up with no problems. Now I will get one to replace it. Thanks
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Sunday, August 28th, 2011 AT 3:08 AM
Tiny
JDL
  • EXPERT
Hope everything works out for you. Have a good day.
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Sunday, August 28th, 2011 AT 2:04 PM

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