Q –My 1987 Carrera Targa was running just fine and then one morning it would not start. I went on line and learned about the possibility of a failed DME relay, fuel pump relay, fuel pump, computer and so on. I ordered in some parts. I plugged in the DME relay and nothing happened. I then tried the fuel pump relay but when I pulled it out, the female terminal pulled out with the relay! Naturally I got excited and figured that I found it but when I jumped direct power to the fuel pump, the car still would not start. When I ordered I got Uro brand parts. What do you know about them and what should I do next. –Steve
A – It sounds like you picked all the “low hanging fruit” so you were on the right track. The DME relay is a good bet and you are wise to have a spare even thought it did not fix the problem. Now that you know about the plug for the fuel pump, you can order that from Porsche and you might be surprised at how proud they are of that part. It is not cheap! To replace it you must splice it in.
This requires some expertise, so if you are not good with soldering or solderless terminals, leave it for a pro. That still might not get your car started. The next test is for spark and for that you have to be careful. The system can stop your heart if you do not take precautions. This too should probably be left to a pro. Things that I have seen which will stop your car cold include a failed temp sensor ground circuit caused by age and corrosion. If your car still has a “single terminal temp sensor,” replace it. If it already has been replaced, do not worry about it.
The next test I would perform would involve the crankshaft speed and reference sensors. That test requires an oscilloscope since simple resistance tests of those sensors yields far too little information. With a scope test of the sensors you should see a strong and consistent signal from both sensors. If one or the other fails, they often do on starting rather than running. Perhaps an engineer can explain this to me, but my theory is that during starting available voltage (11 to 12 volts) is lower than charging voltage (13.8 to 14.2). Finally, if the scope test of the sensors passes both, you could have a problem with the DME which is located under your seat.
Since you have a Targa, is it possible that it got wet? I know it may sound crazy but I know of one car that was left out in the rain and ended up with two inches of water on the floor. It wouldn’t start! After disconnecting the battery, removing the DME, removing the circuit board and drying it out with a hair dryer, the car started and ran! So if you think you have a bad DME there are a few options. Do you have a friend who owns a similar generation car as yours? If so, try your DME in his car and see if the problem follows the DME. If it does, Bingo! If it does not, then you will need to have it flat bedded to the expert of your choice.
As far as the Uro branded parts, most of them are made in China and I do not recommend Chinese parts for German cars. Now, having stated my general philosophy, several German companies are now sourcing their parts from China such as the original manufacturer of the fuel pump relays. Still, I would prefer German. Interestingly, the DME relays which are from an OEM manufacturer come from Hungary and many of the OEM parts from Porsche are sourced from many European countries other than Germany. –MC