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Matt
Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 21854
Experience:  BEng hons Mech engineering, in auto industry 22 years
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just fitted a new DME relay to my 86 porsche 944. Engine will

Customer Question

just fitted a new DME relay to my 86 porsche 944. Engine will fire up, idles for a few seconds then dies out. It also dies out as soon as I touch the accelerator pedal. Can you offer any advice please. PJ
Submitted: 3 years ago.
Category: Car
Expert:  Matt replied 3 years ago.
Hello


this sounds like a lack of fuel and could be a lack of fuel pressure from the electrical pump at the tank.

If the connections to the pump are corroded or damaged then the pump could stop at any time or could not be running at full speed. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse,
Ideally measure the pressure at the injectors and if this is low check the pump as described and also consider changing the fuel filter as if this partially blocked this too will reduce pressure.
Customer: replied 3 years ago.

Hi Matt,


Pump working fine, good fuel pressure at rail but problem persists.


 


I dampened a ragcloth with petrol, opened air intake pipe and covered it with wet cloth. Switched on ignition, petrol vapour sucked into engine, it ran perfectly and throttled up with accelerator. Something is starving injectors, any ideas ?


PJ

Expert:  Matt replied 3 years ago.
Hello


From your description its likely that the ECU isn't opening the fuel injectors, if the injectors are working you can hear them click - its difficult to hear them with background noise so use a long screwdriver like a stethoscope, placing the handle end in your ear and the metal tip against the body of the injector whilst your assistant turns the engine over.
If you can't hear anything check the ECU power is present by measuring voltage at the fusebox and on its relay socket if OK then check the connections to the crank speed sensor and consider replacing this sensor if the wiring / connections look OK