Electrics and the DME relay
Why the DME relay comes up so often, how the fault shows itself and which other electrical points to check.
In short: The DME relay feeds the engine management and the fuel pump. If it fails, the car will not start. A common cause is cracked solder joints inside the relay.
What the DME relay does
One contact powers the engine management (on the Turbo also the knock regulator), a second the fuel pump and the oxygen sensor heater. From model year 1985.5 the relay sits in the relay panel in the engine bay.
Failure pattern
- The engine will not, or only reluctantly, restart when hot and only starts again after 30 minutes to 2 hours of cooling.
- The engine suddenly cuts out while driving.
- Tapping the relay while cranking sometimes helps temporarily.
The relay can be tested with a multimeter and repaired by re-soldering.
Other electrical points
Common causes of failures are corrosion at the fuse and relay panel and weak earth connections; slow pop-up headlight and window motors are also typical. Try every light, gauge and switch during a viewing.
Technical values
Only work with the workshop manual and the correct tools. Do not use unverified values without checking them – wrong tension values can destroy the engine.
Sources
- Secondary source DME (Fuel Pump) Relay Technical Information and Testing
Function, failure pattern and testing of the DME relay.
- Secondary source Porsche 944 buying checklist (PDF)
Buying checklist ordered by area.