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Poor pickup&engine miss firring - F-450 Ford Cars & Trucks

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Crank position sensor fault. Check that the connection is clean and that the wiring to the PCM has continuity. If it all checks out swap out the CKP. The situation you describe matches the last of symptoms below:

Symptoms of faulty crank position sensor

  • Starting difficulty/failure/stall - If the faulty CKP timing problems are severe they may prevent the engine to fire, to fire and then stall, or stall at some random time without warning.
  • Hot engine shut off and failure to restart - The engine may start and run perfectly from cold but will begin to misfire or suddenly shut off after about 15 minutes once the engine has reached operating temperature. This effect is due to thermal expansion of the CKP causing an intermittent break in electrical continuity and therefore the signal output to the ECU is interrupted. Sometimes the engine will restart but fail again after a further 15 minutes. On other occasions the engine will not restart until it has completely cooled down.
  • Misfire - miss-timed spark delivery caused by a faulty CKP signal can cause misfire and back fire events.
  • Hesitant acceleration, acceleration ceiling - Miss-timed ignition due to a faulty CKP signal can be exacerbated by increased engine speed. The engine maybe run evenly at idle but will fail to accelerate properly at higher revs until the engine reaches a power ceiling.

How to check? If the CKP has died completely there will be very high resistance between the device's electrical connections associated with the open circuit. Furthermore spark delivery to the plugs will be absent. First check that the electrical connection is clean and secure; dirt or corrosion can impair an otherwise healthy CKP signal from getting through. If the CKP suffers from a drop in voltage associated with heat increase this can only be detectable with a voltmeter or oscilloscope with a graphical display; an analogue display voltmeter might just be able to show needle fluctuations due to voltage variation output.

2 pin socket (magnetic - sine wave output). One pin is 'ground' the other is 'signal'. A voltmeter set to 2 volts AC should measure a signal in the 0.2 to 2 volts range on the 'signal' pin.

3 pin socket (Hall effect, magneto - square wave form output). One pin is 'reference' (5volts), one pin is 'ground' and the third pin is 'signal'. A DC voltage should be detectable in the 0.5 to 1.5 volt range from the 'signal' pin.

It is important that the voltage measurement take place at start up when the engine is cold and again, 20 minutes later, when the engine has fully warmed up to operating temperature. Often the voltage output from faulty sensors declines with temperature rise.

Posted on Nov 15, 2010


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