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Discussion Starter #1
Hello everyone,

I have been trying to find the problem with my truck it will prime the first fuel and then start then die immediately. I took off the fuel line from the throttle body and while cranking it will keep shooting fuel but will not continue to deliver fuel once engine starts. It will not idle and I cannot hold the accelerator down to keep it running. However it will keep running if you spray gas into the throttle body.

Stuff Replaced

Fuel filter
Fuel pump
All relays on the driver side (ASD, etc)
Spark Plugs & Wires
Ignition Coil
Distributor Cap & Rotor

I appreciate any advice. Thank you
 

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Have you checked your fuel pressure with a gauge? Checked your gas cap to ensure it is vented correctly? When it starts the fuel line that is not connected stops delivering gas? When the fuel pump stops delivering gas have you made sure it is still receiving the necessary voltage to run?
 

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Discussion Starter #3
Thanks for the reply jamesslcx.

I have not checked the pressure yet. Oreily's here wanted 117 dollars to rent it and I'm a little short currently. I checked the cap. The fuel line is connected back to the throttle body when I actually start it. I was just cranking it when i had it unhooked to see if it was getting gas to the throttle body. I have not checked to see if its still getting voltage. I have looked around and it could be something with the ecm only giving power to the ASD for two seconds. I am really at a loss. Thanks for suggestions.
 

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I hear you jab, that steep to rent a pressure gauge. I bought my Innova one on sale at Advance when it was about 25 bucks, it was worth that. Anyway that voltage check could tell you a lot when you get the chance. Let us know because it is a good learning experience.
 

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Discussion Starter #5
jamesslcx I checked power at the fuel pump I have a nifty cut out in the bed, :). It was getting power there with the key turned on. So then I hooked up to the fuel pump relay and i was getting 12.38 there but once I started the vehicle that voltage dropped to like .37 or something. That seems to be not good right?
 

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Discussion Starter #11
jamesslcx i changed the ecm and its the same problem I am totally lost. I have replaced everything I can think of. Thanks for your help.
 

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Damn, I thought we had it Jab. Knowing me I would run a 12 volt wire to the pump and bypass the factory wire. I'd make sure it was fused and operated when the ignition switch was on. Would that work until we figured the problem out?
 

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Discussion Starter #13
Yeah I am going to try that and see what happens. I figured if anything I will go through all the wiring. Thanks again jamesslcx
 

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Discussion Starter #14
jamesslcx, I had a thought is there anything on the 1988 3.9L throttle body engine that reports the RPMs to the computer? I was looking around and saw something about a safety feature where the key has to be turned on and the engine show RPMs for the fuel pump to keep pumping. Thanks
 

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Jab, you may be on to something but I'm not sure. I don't know of anything on your throttle body that informs the computer of rpm. We know the tps lets the computer know about how much throttle is given, the map sensor informs of load on an engine, the coolant temp sensor acts like a choke letting the computer know the temp of the engine so it can adjust fuel amount. Whatever is wrong with your engine is something small it's just a matter of figuring it out, I was positive another pcm was the answer for you. When you first turn the key to on do you hear the fuel pump run? There has got to be a reason the pcm cuts back on voltage to the pump.
 

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Discussion Starter #16
James, yeah Im not sure of anything either. When the key first turns on I do hear the pump run. It does prime it. Even when cranking it spits fuel but as soon as it starts no more fuel. I have replaced pretty much everything except the sensors you mentioned.
 

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Discussion Starter #17
James,

Get this I rigged it to where the fuel pump is on all the time with a toggle switch for testing purposes it still doesn't run. Totally at a loss here. Thanks for all your help.
 

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Jab, I've never seen one act like this. I am at a loss also. Let me try to figure something else out. My brother bought a 89 Dakota with similar problems believe it or not, he thinks replacing the ASD relay will fix his problems, time will tell he may be surprised.
 
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