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Need elect. help with fuel pump relay

This is a discussion on Need elect. help with fuel pump relay within the General Help forums, part of the LSx Technical Help Section category; I just got a used 98 T/A, auto. I'm trying to work through some of the bugs. I found out ...

  1. #1
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    98 T/A A4

    Need elect. help with fuel pump relay

    I just got a used 98 T/A, auto. I'm trying to work through some of the bugs. I found out that the previous owner (idiot) jumped out the fuel pump relay. When you turn the key on, the fuel pump comes on and stays on. I have 12v. at the relay, but don't have a signal from the computer to close the relay. Any help would be appreciated. Am I hurting the car to run it this way?

  2. #2
    Veteran 0rion's Avatar
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    98 Formula
    06 duramax

    Do you have a haynes manual? The schematic for it is in the back of that. I have a page or two scanned that shows those wires. Looks like blk/wht and Dk grn/white are the relay wires. I can email you the scans or I can link them to you in PM if you want them. They are a little large to put in the thread and will cause load problems for dial up people trying to view your post to help you out. Are you sure the relay is good?

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    I have the schematic and the manual, and yes those are the wire colors. But there is no signal voltage on the grn/wh wire from the comp. to the relay, to tell the relay to close. It's either a comp. problem or a fuel pressure sensor problem. I don't know where the fuel pressure sensor is, I would assume it's in or on the tank somewhere. Is it hurting anything on the car to run it this way till I fix it?

  4. #4
    Veteran 0rion's Avatar
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    98 Formula
    06 duramax

    Have you tried swapping out the relay to make sure it's good? That's the cheapest place to start. I answered your other question in that post. The sensor is on top of the tank attached to the fuel pump module. I tried to do some research on your problem but didn't really come up with much. I'll keep looking and maybe between the 2 of us we'll find something. Does your car have the air injection still on it or is it removed? It looks like that might be on the same circuit as the pump relay. I'm not great with schematics so that could be totally off base. Those wires coming from the pressure sensor are pretty easy to get at. It's on the drivers side rear bulkhead just above the rearend.
    Not sure if it's hurting much running like that as long as you go ahead and start the car. It wouldn't seem to be a problem IMO. Hopefully you can get it fixed pretty quick. Keep me posted and if I find anything I'll post it up.

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    Thanks for the feedback Orion. The relay is good, there is no voltage coming from the ECU to tell the relay to close(grn/wh wire). Maybe the ECU is bad, I hate to take it to a stealership. I'll let you know if I get it figured out.

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