Thursday, September 8, 2011

1997 ford expedition starts and dies in few seconds?

The PCM can be tested by dealer, its a tool to test the PCM.If its shorted, then PCM needs to be replaced.-------
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But there are other possibilities too line faulty fuel pump relay, or faulty pcm relay or faulty antitheft module or faulty wiring or connections.----------



Signal flow has brought me through the following:
12v at fuse 19 - fuel pump
12v at fuel pump relay terminal 30
6v at fuel pump relay terminal 87. this 6v is coming from the PCM, the relay is not engaging.
10v at fuel pump relay terminal 85 - this is fed by the PCM

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The fuel pump relay and pcm relay both located under hood fuse box in the engine compartment:----

What are you reading on the coil side of the relay on pin 86? Are you getting a good ground from the PCM on pin 85?

The coil side of the relay has to energize to create magnetic field to pull the switch side closed. I suspect that you are not getting enough juice here to do this. Also since when you jump pins 30 and 87 and get 12V to the pump and it still doesn't run confirms this. Pin 86 gets its power from the PCM relay and I suspect your problem is here .

Here is the wiring schematic for this

graphic

Check power on pin 30 and 87 of the PCM relay see if you are not getting the same results there also. If so then jump pins 30 and 87 and see if it runs then. If it does then check the PCM diode I suspect that this is your problem.


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So this is what I got:

PCM diode passes 12 volts in one direction

Fuel Pump relay pin 86 gets 12v when key is on

Jumped 30 and 87 on PCM relay and same thing, not engaging fuel pump relay

Power Distro Fuses in engine compartment fuse box fuse 30 & 24 , check this fuses,

If there is No continuity on pin 85 of the Fuel pump relay to ground, the ground it and the relay closed so this tells you that the PCM is not grounding the relay.

To test this open up the wire harness to the PCM and checked continuity between all ground pins and ground.

Engine fuse module fuse #1 (pcm) good and continuity to battery terminal and to the pcm pin 55 so this will confirm that you are getting power to the pcm
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NOW ONE MORE THING:----
What is the anti-theft light doing when you turn the key to the run position?



The antitheft light is flashing, Will

the pats cut voltage to the fuel pump via he PCM.


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On this vehicle it does not have a starter interrupt it disables the fuel pump.

If the anti-theft light is flashing rapidly when the key is turned to on position this is your problem.


When you turn the key to on position the theft light should come on solid for about 2 seconds then turn off.

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BUT IF ANTI THEFT LIGHT IS CONTINUOUSLY FLASHING THEN, you need to test the anti-theft module wiring.------
The wiring is shown below:----
graphic