C4Spolar

Hello Rennlisters.

I'm having a big issue with my fuel pump. No power to the pump at all, I checked the fuse and replace it with a new one, replace DME relay, had the ECU checked and still no power to the pump. The battery reads 12.6V. I also plug direct 12v to the pump and the pump works.

When ignition on no voltage on the 2 wires that feeds the pump. I think the problem is between the DME relay and the pump meaning bad wires. Is there a way to bypass the relay and direct feed power to the pump? Electrical trouble shooting is not my strength.

Any other suggestions.

Thanks.

pp000830

If you pop the cover off the DME relay and plug it in you should see the two relays inside of it actuate. One when you turn the ignition on and the other when you turn the key further to the start then back to the run position that controls the fuel pump. If you do not see both internal relays move the problem is upstream, ignition switch / the DME-ECU or the wiring harness wires/plugs-sockets. if you see the relays both move your problem is downstream. To check downstream issues, check the continuity from the DME Relay socket to the pump or with the pump attached the resistive load caused by the pump that disappears when you detach it under the car. Also, DME Relays can be DOA new, out of the box and ignition switches do fail but are easy to replace.

Andy

pp000830

Here is the full set of wiring diagrams to scope things out.
https://993servicerepair.blogspot.co...-diagrams.html
Andy

IainM

With the DME relay out, you could test for the resistance of the pump on the DME socket, probably pin 5 but maybe 7.
not sure what the resistance should be, maybe 5-20 ohms but it shouldn’t be 0 or infinity (short/open)
test to ground/chassis

71-3.0-911

Make a jumper and bypass the relay. It'll be fine just for a quick check.

Foxman

This. “Make a 3-way jumper to (temporarily) replace R53 ...... connect pin 30 ( +12V) to both pins 87 & 87b: try to start the car.

If it starts and runs, the relay is defective. If that is the situation, either repair or replace the relay.” (Courtesy Garth S)

C4Spolar

Thank you all for your help.