Q: Engine swap project, fuel pump relay wont engage from the ECU.

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I'm swapping the engine out from an Audi A6/C4 2.8 V6 (AAH) in an Audi 90 NG.

I got the engine wiring harness in, tho NO engine in place.

I wire up the ECU, green to the fuel pump relay (I used the 2.3 Audi 90 relay I had), black to 15, and black/green with that grounding "o ring" end to ground. small red goes to 30 (B+) and that's it. I haven't hooked up anything, because its not needed as by the schematics.

I turn the key to ignition with the ECU in place but no engine, fuel pump relay engages and primes for 2-3 seconds and shuts off. I turn the key to off position, then to ignition again, NOTHING. Absolutely nothing happens. I tried removing the battery terminals and putting them back in to reset the ECU; no. I have power everywhere I should. Afaik I only need the yellow thermo-fuse holder to be on when the key is on ignition. The relay does NOT engage no matter what I do. It almost sounds like it wants to, but sounds like it has no power? It shakes JUST A TINY bit when key is

My car has 88000 miles.
My car has a manual transmission.

Hi there. Check the wiring from the fuel pump relay to the computer and see if there is a break in the wire. If there is no break in the wire, then check the power to the pin where the green wire connects. If there is power without the yellow thermo-fuse and there is no power with the thermo-fuse, then there could be an issue with the ground circuit on the computer. Check the ground to the computer and make sure that it is clean and tight. If you need further assistance with the fuel pump not engaging, then seek out a professional, such as one from Your Mechanic, to help you.

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