Porsche 944 turbo dme relay troubleshooting (1986-1991) pelican parts diy maintenance article electricity receiver definition


If your Porsche 944 will not start or suddenly dies on you, one of the first places you should check is the DME relay. On the older 944s, the relay is known as the fuel pump relay and is located on the fuse panel under the dash on the driver side. On later 944s and 951s, the relay is located in the fuse /relay panel in the rear left side of the engine compartment close to the windshield and A-pillar. These relays are prone to failure, a lot of failures. They usually fail from broken joints in the circuits, but they can also fail from the diode and or have issues with heat sink.

This article will show you how to check your relay for proper function and show two emergency stop gaps to get you home, but these stop gaps should only be used in the most extreme of emergency situations. If you are going to drive a 944 or 951, invest in a couple of extra DME relays and always carry a spare. There is even room in the fuse box for the spare. With a proper functioning relay, buy a spare and swap it out with the good relay. If the car starts and runs with no problems, then you know the new relay is good. Switch them back and place the spare in the fuse box. While all of these tests will help track down a problem, it is still easier just to install a known good relay.

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All the gauges in the cluster shut down and don’t come back even if the car dose start again. It takes a while for them to come back with random restarting and waiting.Is it possible that the faulty DME is affecting this Ive ordered a new one? Or is it a completely different problem.all the fuses are good.

Comments: My 85.5 944 was running perfect. Backed into the driveway and next day turns over but no ignition. Never had a no start from this car. I’ve been through all the obvious things listed, but no spark still. Does this system use a resistor like the the old days? Or is the transister in the DME what I should be testing? If so, how? I know how to get access, just not sure what I’m measuring.

Comments: Thanks for the info. Power to the sensors come from the DME and then goes back to the DME correct. It has fuel pressure, no spark. The sensors were new last year and fuel pump this spring. I do have a feeling it may be the sensors, I was hoping for a way to test them. Thanks MAK54

Followup from the Pelican Staff: The DME is only the receiver of the analog signal, those sensors should produce an AC voltage when cranking the engine, however I have not had much success testing them by voltage. They sometimes test OK, but when I swap them the car starts. If you find a spec for the AC voltage when comparing the two please let us know! The adjustment can be off from sensor to sensor so I suspect that is why testing for a/c voltage is not a perfect test. You may however test the resistance between the first two terminals on the sensor connector and the resistance should be between 800-1600 ohms, then between the first and third terminals should be no continuity. I have found however that these tests are not absolute. – Casey at Pelican Parts

Comments: I did the McGyver fix and still no start. I have battery voltage to both sides of the coil but no pulse. I disconnected the speed and timing sensors at the bell housing which are new two years ago, and haven’t any voltage to them. I fear a DMC, but want to make sure. The car is a 1983 944. Any other ideas before I spend a bunch of money.

Followup from the Pelican Staff: Ok, so you have no spark, now an important piece of the diagnostic equation is do you have injector pulse, and do you have fuel pressure? You will need a noid light set, to plug in to one injector. http://www.pelicanparts.com/catalog/ShopCart/TOOL/POR_TOOL_CAT447_pg28.htm