Porsche Repair: 84 944 no start., mark sensor, reference mark

Question
Hey Dave,
   I have an 84 944 and for the life of me I cant figure ot whats going on. I have a no start condition, but, here's the kicker.I have both sensor signals,good fuel pressure,Spark , and injecter pulse. If you spray it with starting fluid,it'll run for a sec then shut down. I put a new engine in it with 70k on it and it hasnt been right yet. I have tried replacing everything.DME box, Relay,injectors,fuel pump. you name it.. Any help would be Absolutely GREAT...  Thanks ..Gordon

Answer
Hi Gordon,

With your analysis, there are very few things left that could be the culprit, but I know the feeling...darned frustrating!

This is a bit obscure, but your car's computer needs a signal from the reference mark sensor telling the computer how many times the crankshaft is revolving, and this is critical during the engine cranking phase and the initial start phase.  It's clear from the wirng diagram the sensor has a black plus a yellow wire leading to the computer but I don't know exactly where it's located.  Intuitively, it would be pointed at the crankshaft at the damper with all the timing marks on it. If you can find it, you should be able to test it by watching for voltage while cranking.  If there's none, that's the problem...or...there's also a possibility the sensor could be there but mal-adjusted.

Dave