great post jacob............. I can see that you have been extremely thorough in your testing and followed the Porsche Workshop Manual .I'm impressed ...Good work !;)

With all the work you have done and the parts replaced you have to wonder what on earth could still be wrong with the car but Springs post highlights potential faults that are often overlooked . How many owners possess a Noid light !? .
Ground or earthing points too are so often overlooked . owners think that they are such a mundane component that they couldn't possibly be the reason for a failure.

On the late 944 the ECU is located under the passenger carpet . Above the ECU alongside the fuse relay box there are 2x vital ground points for the ECU under the dash on the scuttle .
I cannot remember where the ECU and the fuse/relay box and ground points are on the early 944 but I believe that none of them are in the same place as the early cars
It is essential that you find these ground points and remove and clean them when you replace the wiring loom as a lot of the work that the ECU does is by grounding components using those specific ground points

Good luck with the rewire I shall monitor progress with interest

Thanks to this forum (and Vitesse John), this year I learned the awesomeness of a simple (and cheap) 12v LED light for diagnosis. This can be had at any electronics supply.

So easy to see injector signals, coil signals, lots of signals. Everyone should have one in the car's armrest or glovebox. Quicker & easier than a voltmeter, noid light, etc

have you done a search on this forum and the net for '944 starts and dies ' ??

Firstly are you using the DME relay or have you fitted a 3x wire bypass whilst you are testing ? If you are using the DME relay again then that would be my first port of call.
Stick the bypass in there so that everything is supplied with power constantly and try that

If it were me I would fit a fuel pressure gauge to the fuel rail so that I could monitor the fuel pressure all the time when starting and running the car. This will eliminate fuel pressure being the culpret

Either you are losing fuel air or ignition spark and knowing which would narrow down your search considerably.

have you got the 3x wire bypass fitted whilst you are testing ?
I don't understand why there is a reluctance to do this . it immediately eliminates a lot of components .

Don't rule our your ignition switch having a bad connection or the base connector for the DME relay in the fuse relay box .

well obviously you will have a much better assessment than me as I'm 1000s of miles away lol.

The 3x wire bypass doesn't just supply a permanent 12v+ supply to the fuel pump . It does all of the many jobs that are normally done by both of the relays inside the DME relay can .

If everything thing is going dead when the engine cuts out thats is a very important bit of information and really helps direct you to the problem source.

What is it that could cut power to the whole ignition and dash ? .......
I would look at your ignition switch first .
I will have to refresh my memory from my electrical schematic which will take a while but do you have a factory alarm or aftermarket immobiliser fitted to the car ?


Jacob I know that you will already have checked the battery and battery terminals but just humour me and check again by removing the terminals completely and checking the battery cables and chassis ground. If you have a jump lead you could attach one end to the negative battery terminal and the other end to somewhere on the engine or gearbox .Try starting the car This will bypass your negative battery ground wire and could show up a poor connection somewhere

mmmm just a thought , you replaced the crank position sensor and speed sensor didn't you ?
I wonder if the ECU is shutting down the engine because it isn't seeing sufficient engine speed ......
its a safety feature that prevents fire in the case of an accident . The ECU won't normally let the car start if the revs are not high enough but I suppose it is possible it could start and be shut down by the ECU. if the speed sensor is sending faulty information.

you said previously that everything went dead ?.......is that different now

you need to buy a new battery for the car. You cannot expect a battery booster to supply enough amperage to power the car when its running. Its not about volts otherwise we would be able to start the car on a torch battery. its all about amperage or amphour rating .
You are still hitting things at random .

If you have a fuel pressure gauge attached to the fuel rail....... tell me exactly what the fuel pressure is when it is running and what exactly happens to the fuel pressure the second the engine dies . That will tell me something useful and help tremendously with the diagnosis .

that is not the most accurate gauge on a car but the most important thing it is telling us is that the engine is not cutting out due to the fuel system suddenly losing fuel pressure .

Good we are getting somewhere.
We can probably assume that the injectors , the fuel pump and the non return valve are not leaking . Same goes for the FPR and damper and the fuel system generally.

Because the car is actually starting and running for a few seconds we can also assume that the DME relay the ECU , the crank position sensor , injectors , and secondary ignition system are also all working ......otherwise the car would not start and run.

So we are now looking for something that would cause one or more of those components to stop working as they should .