[ischmitz]

Greg,

I'm still puzzled by your data. You say fuel pressure was 35 psi during cranking. That sounds about right (spec is 36 psi, engine off, fuel pump jumpered). It wasn't clear whether this was due to residual pressure from jumpering the pump prior or because the pump ran during cranking. Further you say you are going to check if the pump is running while cranking.... so you are not sure either?

FYI, the Porsche WSM calls for several checks for the fuel system:

- static fuel pressure with engine off: 36psi
- residual pressure: >14.5psi after 20 minutes
- fuel delivery rate 0.85 liter in 30 seconds


Sounds like you have done (1) and (2). Maybe check (3) delivery rate while you are at it.

I'd still be curious to verify that the DME relay is switching correctly. For the first stage it is easy to just listen to the relay while turning the key to RUN. Every time you turn the key to RUN you will hear it click. I believe that is working as your ICV comes on fine.

For the second stage the check is a little more difficult because of the noise from the starter. The Porsche WSM suggests an assistant listening to the pump while cranking the engine. Alternatively, you could try to place your hand on the DME relay and see if you can feel it click while cranking. Or you could temporarily disconnect the yellow spade connector at the starter relay. This will prevent the starter solenoid from kicking in.

As a matter of fact you can turn the key to RUN, disconnect the yellow spade connector from its terminal at the starter and then momentarily touch it to the big red wire on the starter relay. This is equivalent to putting the key in START (energizing terminal 50). You should hear the fuel pump running right there.

A little safer: Get back up and turn the key to START and you will hear the second click of the relay and the whirr of the fuel pump coming on. If one or both don't happen you found a critical issue: Its either the DME relay (not very likely as you tested two, but not unheard of either) or the DME itself because you have tested the fuel pump can run.

On a side note: Rather than shifting towards other tests now I'd follow one lead to the end first. Keep in mind you found damage on the PCB inside the DME and it's highly questionable that replacing R750 is a sufficient repair. Once you confirm that you have the fuel pump running while cranking and decent fuel pressure it's time to move to the next set of tests.

Ingo