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Thread: 3.5 v8 revs real high then shuts off when trying to start

  1. 13th July 2014, 06:27 PM #1
    Zacs
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    3.5 v8 revs real high then shuts off when trying to start

    my 3.5 v8 will start but only runs for a few seconds. It will automatically rev to about 4000 rpm on start up sits there for 3 seconds or so then shuts off. Any help on where to start looking would be great.

    I've replaced fuel pressure regulator and the stepper motor.
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  2. 14th July 2014, 08:25 AM #2
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    Kevin B
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    have a listen for yuor fuel pump when turning the key on, does is buzz, if not there is the problem, i had the same issue and that was the cause

    Kevin
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  3. 14th July 2014, 12:25 PM #3
    Zacs
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    fuel pump appears to be working. I did find that the fuel pump relay is switching off after 3-4 seconds of running.
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  4. 14th July 2014, 12:31 PM #4
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    Kevin B
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    yes i believe thats correct at Key on the pump primes then turns off after 3-4 seconds, once engine starts the relay comes back on and pump runs till engine turned off, thats my understanding of it.
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  5. 14th July 2014, 01:21 PM #5
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    clubagreenie
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    Replace the relay, if the timer circuit is built into the relay this could be the issue.

    Otherwise, if its a flap AFM and its like early.Togo stuff the flap also switches the pump. No airflow no pump power so if it stalls in an accident the fuel is shut off. Try holding the flap open slightly.
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  6. 14th July 2014, 01:48 PM #6
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    Kevin B
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    thats a thought, also check the inertia switch as well, you said its a 3.5lt, on my 93 model 3.5 the inertia switch is located under the dash on the drivers side firewall above the brake pedal, little black box with a button on it, long shot but worth a look.
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  7. 14th July 2014, 02:01 PM #7
    Zacs
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    the relay turns off after the engine has been running for 3-4 seconds. I've tried a new relay. And its not a flapper afm .
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  8. 15th July 2014, 08:41 AM #8
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    Need to work out what's controlling the timer circuit then. Maybe swap ECU's with a known good unit to see if it sorts itself out.

    Or test the power input and the switching input to the relay to see which one is turning off. If it's the switching wire (that turns the relay on) then whatever is controlling that needs looking into. If the power supply to the relay is turning off then it's being controlled by a secondary circuit (as a safety backup?).
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