This has been about 5 months of tinkering...on and off. 1986 951, no start. So far, i have replaced, plugs, DME relay, both reference sensors, i changed the DME and KLR to another pair of used but supposedly working ones. Now today i checked for spark, nothing. I was quite certain that i had a ton of spark a while back while working on it but i may have been mistaken. I also don't have a ton of fuel. I can remove the hose feeding the fuel rail and it trickles at best. It seems that it builds up a few table spoons of fuel and that is about it. So i really don't know where that leaves me. I have no spark at the coil, but have 12+volts. No spark and no fuel lead me to think that it is either wiring or the second set of computers is screwed as well. I really do love my Porsche...that is becoming a mantra, keeping me from burning it!

 

There is nothing wrong with taking it to a shop and having a professional look at it for you.

 

I am not against taking it to someone smarter than me Doc! The only problem is that the nearest decent Import mech is 3 hours away. I have been doing alot of reading on here. This site ispriceless to us back-yard mechanics!! Thanks for all your help and input in here Doc! I am going to change the coil (looks to be factory, and not getting spark off of it), and the cap and rotor (look like they need it, corrosion etc), and if that dosen't help than i guess it makes the trip to the city. Again, thanks for everything Doc!!

 

Ok, I'm kind of new to the Porsche 944 Crowd but I have worked on alot of diffrent brands so I'm going to make a few assumtions about how things work if I'm wrong let me know as it will help me in the future. To get this bad boy started you need, fuel, spark, and compression.

1.) Everyone seems to be at the concolusion that your tach will bounce if your primary speed sensor (the starter ring sensor)is good. So you can test that way and then swap sensors. You may also want to check the electrical connections to the DME. Here is another way to test the speed sensor.
http://www.clarks-garage.com./shop-manual/ign-02.htm

2.)Most cars that use a Crank/Cam posistion sensor of some typeand electric fuel pump don't fire the pump until it detects movement crank movement. If you speed sensors aren't working that could be an issue. You get an initial prime when you turn the key and then the pump shuts off. So, it doesn't run for very longever after you turn on the ignition. I would recommend finding the fuel pump relay / test point and jumpering the pump on with fuel hose in a bucket or something. If that works its not the pump if it doesn't go back to the fuel filter remove it and retest. If that doesn't work its wiring or the pump.
Here is a procedure via clarks garage http://www.clarks-garage.com./shop-manual/fuel-04.htm
Something not mentioned on clarks is to try and test the pump at the pump using a battery or battery charger. I would try this also if all else fails.

3.) Checking the coil see, http://www.clarks-garage.com./shop-manual/ign-04.htm

Good luck hopefully you get it to run.