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

asked by on November 18, 2016

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.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

What others are asking

Large EVAC leak.

Hello. If the gas cap is verified to be good, the most common culprits are the purge valve and charcoal canister. If you would need help having this checked, a certified technician from YourMechanic can come to your car's location...

Won't start after filling gas tank

The most common cause of hard or no start after getting fuel is due to a leaking purge valve leaking vapors into the engine when refueling. This will flood out the engine causing problem. Have the purge valve checked for...

I have a very loud knocking sound from the front driver side of my 1991 Jeep Cherokee Laredo 4x4

Hi Taylor. Thanks for contacting us tonight. A loud knocking sound coming from your front wheels can be caused by wheel bearings or inner transaxle components. If the noise does not come on during reverse, then it's likely a forward...

Car starting, idling, and then stalling

Hello. If the engine will only run for a short period of time then it may have a failing fuel pump or an electrical issue. Being that you stripped out the fuel filter connections, the metal lines may need to...

1991 chevy g20 van replaced wih new fly wheel and starter after 2 days getting clanking sound when i first start vehicle

You should check to make sure the starter bolts did not come loose and remove the lower inspection cover for transmission and check to see if flywheel teeth are damaged or flywheel is loose or bolts for torque converter are...

Car won't start even after I replaced the fuel pump.

If the fuel pump has been replaced and your issue is still fuel related you may have a clogged fuel filter or malfunctioning fuel injectors. If all of these parts are known to be functioning properly the issue is likely...

Coolant leak coming from behind the radiator

The coolant leak can only be pinpointed after an inspection but a leaking hose in that location would not be unusual. Coolant leaks can sometimes be either a cause, or a consequence, of overheating. Be sure not to drive the...

Gas not getting to the throttle body

The problem could be a bad fuel pump, but I would start with checking the Inertia Cut Off Switch. This switch is in place to stop fuel delivery in the event of a collision, although they sometimes trip when you...

Stalling fuel pump flapper on 1994 Ford Probe

Hello. The fuel pump on your vehicle is powered through the fuel pump relay through direct battery power. The fuel pump itself is located in the fuel tank and there is not an access panel to easily change it. The...

Related articles

Top 10 Factors to Consider When Buying a Luxury Car
The The idea of owning a luxury car is appealing. The glossy paint, swoopy lines, and prestigious badges speak of the owner’s success in life, while the interior opulence offers scented leather surfaces, high-tech telematic devices, and all the creature-comfort...
How Can I Keep My Fuel System Clean?
Proper Proper maintenance of the fuel system is crucial for consistent long-term performance of a vehicle. The most easily clogged parts of the fuel system are the fuel injectors themselves. There are a number of ways this can happen: ...
How to Replace a Door Lock Relay
Electric door locks work via a door lock relay located near the brake pedal, behind the stereo, behind the passenger air bag, or under the hood.