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Video trouble shoot!! 4.0 B2 fuel pump wont turn off, and no start???


BabyBronco89

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truck started up and drove fine all the way to work, got to work parked it, went out on my lunch break to start it and she wouldnt start up just dry cranked.
i thought maybe i was out of gas..., after putting in two gallons and still no start i started at the relays theres three relays a ecm relay fuel pump and a starter relay every relay seems to be working correctly bought a new ecm relay and it didnt do anything tried swapping them out and it did nothing

when i turn the key on your supposed to hear the fuel pump click on then shut off but it doesnt shut off.
the fuel pump keeps running and sounds like its gonna explode from pumping to much
im thinking that the computer is what tells the fuel pump to shut on and off, so maybe the computer has gone bad? how do i test this?

i seem to have plenty of gas in the fuel rail????

thanks heres my lil video i made

let me know what you think
http://www.youtube.com/watch?v=SjB2-mPxNL4
 


Protowrxs

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Just a Guess:

Did you check the fuel pressure regulator? Could the diaphragm be leaking through to the intake and thus no real fuel pressure?

That didn't seem like a lot of pressure when you released it based on my experiences at least. That could force the pump to run continuously and possibly keep it from firing if it is flooding it. Could check the oil level too and make sure it's not pumping gas into the crank case. I'm not sure if the EEC cycles the fuel pump or not? It doesn't know what the fuel pressure is, just that the pump relay is on or off.

Anyhow, just an idea - will be interesting what the final resolution is. Good luck!

-Stephen
 

BabyBronco89

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no it is definately getting gas it was a very healthy stream just like it always is...
although im with ya on the maybe getting too much gas

so what turns the pump off does the sending unit itself sense this?
but im going to try and get a computer tom so i can rule that out, because i was reading some stuff about the 5.0 comupters doing the same type of thing when they failed?

any one ever had a 4.0 computer fail?
what where the symptoms?
 

Protowrxs

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Could be the computer turns off the pump after the prime if the engine is not running. That would make sense. If you can locate a computer I guess that would be an easy enough swap to make sure if that is the problem. May be it's just not firing the injectors.

Easiest to pull computer codes on it and see if it knows there is something wrong or not or passes self test.

One other idea, did you try opening up the throttle while cranking. I debugged a 5.0 with a dead IAB that was closed and would not allow a start unless the throttle was cracked some. Started but wouldn't idle so that was easy to figure out. Fuel pump didn't act like that though.
 

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any one ever had a 4.0 computer fail?
what where the symptoms?
Computer failure can manifest in many forms.

The fuel pump relay is run by the PCM. The pump get a 5 second prime and then shuts down until the computer sees a rotational signal from the cam sensor.

Pull the fuel pump relay, if the pump still runs full bore you have a short to power somewhere. If they shut down test the fuel pump relay. The two smaller pins should NOT have continuity to each other with the relay out. If they don't, check the two-tone wire to the relay for continuity to ground with the key off. If none, get a computer.
 

BabyBronco89

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Alright that's the answer I'm looking for :)
I pulled the fuel pump relay and it stopped my pump. I then swapped it with another relay and it still did the same thing. Won't cut off,
So I need to now make sure that that relay is grounded out properly.
Which I will get to later in the evening right now I'm at work and don't have a multi meter with me,
But I'm leaning more and more twords computer failure

Thanks once again!!!
 

BabyBronco89

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okay so went to the pick a part yard to try and find a 92 auto 4.0 computer.

long story short i couldnt find one but i got it running off of a 94 4.0 computer

can someone tell me what the differnce and compatibilty issues will be?
i can tell you i now have a check engine light on where as before i did not.
but it only comes on when the car gets warm
 

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