Need Help - weird problem

nick041881

nick041881

Member
Hey guys,

I have a weird problem that I need a hand with. I am trying to start up my new motor and I am running into this problem:

When I attempt to start the truck with the fuel pump on and 43psi to the fuel rail the truck fires but will not idle. The motor shakes and sputters and as soon as you let off of the throttle it dies.

Disconnect the fuel pump.

Start the truck. The truck now with 0 psi to the fuel rail starts and idles.

It will not run with the fuel pump on, but will run with the fuel pump off. I thought that this was impossible, but i guess not. My only guess is that the fuel pump draws so much power that is is causing the computer to suffer/lose power. Does anyone have any ideas?

Modifiactions:
Built motor
83lb fuel injectors
F.A.S.T. engine management- file ran absolutely perfect in old motor
Aeromotive A-1000 fuel pump -8 feed/return - psi gauge on rail

This combination has worked fine in the past and no configurations have been changed besides a shortblock rebuild.
 
kessler

kessler

New member
Re: Need Help - weird problem

To me it sounds like a ground Problem. But thats a far fetched guess.
 
nick041881

nick041881

Member
Re: Need Help - weird problem

As per your suggestion I went and checked all of the grounds. I screwed up when wiring the power to the alternator and accidentally powered a wire that was supposed to be grounded. I will find out if that was the problem tomorrow night. I am done for today. Thank you for the suggestion!!
 
kentuc

kentuc

Member
Re: Need Help - weird problem

That is the problem. The fuel pump is powering through the ground and grounding through the ignition. A reverse polarity.
Glad to hear your up and running again!
 
M

MadPSI

Member
Re: Need Help - weird problem

nick041881 said:
As per your suggestion I went and checked all of the grounds. I screwed up when wiring the power to the alternator and accidentally powered a wire that was supposed to be grounded. I will find out if that was the problem tomorrow night. I am done for today. Thank you for the suggestion!!
Click to expand...

Oops... :)

I'd assume that that was the cause of the weird noise coming from the alt when you switched the truck on.

That's probably going to fix a few other issues, like the dash instruments might work now... :)
 
nick041881

nick041881

Member
Re: Need Help - weird problem

Well, I made sure that those wires were grounded and still the same problem. Anyone have any other suggestions?
 
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