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Will not start

Tiny
DAVIDANDSHERRY
  • MEMBER
  • 2003 FORD F-250
  • 5.4L
  • V8
  • 4WD
  • AUTOMATIC
  • 100,000 MILES
We have replaced the fuel pump and filter. The truck ran good for three days, and now it won't start. It cranks and cranks, but won't start.

Earlier today I pushed the reset switch, but I didn't think it pushed in. About five hours later I went out and tried to start it. It started right up. Could it be a faulty reset switch?
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Tuesday, March 19th, 2019 AT 11:57 AM

1 Reply

Tiny
SCGRANTURISMO
  • MECHANIC
  • 4,897 POSTS
Hello,

This sounds to me like it could be an intermittently failing Crankshaft Position Sensor (CKP). These are really hard to diagnose because they usually work great when the vehicle is cold, but as they warm up they start to fail. The CKP sensor works by keeping track of the engine in it's four stroke cycle. The Power-train Control Module (PCM) AKA, "computer" uses this information to fire the spark plugs and send the duty cycle to the fuel injectors.
I have included in the diagrams below, two different factory tests on your vehicle's CKP sensor. Please go through them and then get back us with what you find out.

Thanks,
Alex
2CarPros
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Tuesday, March 19th, 2019 AT 4:12 PM

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