Hi guys,
I have had an ongoing issue with my Porsche and with no useful mechanic in my area willing to help I intend to fix this problem at last by myself, with the help of this forum

I have a 964 C2 manual that will not start.
She splutter starts usually on the third attempt when cold,
When hot she turns and turns but no luck starting,
I have put in a brand new fuel pump,
I have put on a brand new aftermarket DME from design911,
When I take off the old DME relay cover I can manually prime fuel pump and she starts perfectly,
The car is idling/running and driving perfectly in general,
I have just got immobililser inspected and removed, which I believe it was already removed as it made no difference to starting issue but got charger €350 all the same...

The fuel filter I'm told was replaced two years ago, ±500 miles ago, and only ever e5 fuel.

Attached video is after 3 mile drive.

Please help. Thanks

 

Just to clarify, if you manually jump the old DME relay, the car starts perfectly both when hot and cold? Did the new DME relay from Design911 work initially?

 

when I jump the old DME with cover off the car will start hot or cold. The new DME didn’t have any affect, problems persists.

 

That's interesting. I had hot-start problems and the solid-state DME relay from Ftech fixed it immediately: https://www.ftech9.com/new-products/993-ssr-pp. To me it sounds like the relay you got from Design911 is faulty, but that's my only somewhat educated guess.

 

I considered this product before and was tempted. I think I will order it now, should I pay extra for the diagnostics?
a mechanic warned me this could just be covering up an issue that will continue to linger and get worst… what’s your thoughts?

 

Hoping others who are more familiar with the entire fueling system chime in, but if manually jumping the original relay resolves all the problems, I'm not sure I understand how another part of the system would be at fault.

I suppose having the diagnostic feature of the Ftech would be useful. I didn't opt for it but seems like a good idea in your case.

I will say the pump prime feature not only eliminated hot start issues, but just makes hot startup a lot more "satisfying" (in that the engine just starts immediately and doesn't sputter at all).

 

That's a very good point,

I have ordered one, paid the extra 20 as shipping was so high that the difference is minimal.
Will post my results in a few weeks when it arrives... snailmail

 

Have tried an OEM DME relay?

 

The only other part I can think of is the fuel pressure regulator. The membrane inside the part can go bad and it won't hold pressure. Usual symptoms are fuel in the intake and start up issues. Did you clean your ISV just to eliminate another possible issue? Easy to do with a bit of carb cleaner. Your issue sounds more like fuel pressure related but it won't hurt to clean the ISV.

 

We were on a road trip and a fellow 964 owner had his car cutting out and at times not restarting.

We tried a spare DME and it would start but cut out a few Km later.

The car was flat bedded to a mechanic who eventually discovered that the wiring under the DME relay was loose. So it was not the DME but the wiring it uses.

 

Fuel pressure regulator is what I'd check after DME, but the crank position sensor is another thing that can start to fail in odd ways, and its cheap to replace.

 

My car had a broken solder joint in the alarm module that would randomly shut off the DME relay. If jumping the relay manually fixes the issue and you can absolutely rule out the relay itself then you must dig into the wiring diagrams and find/test/jump every possible circuit that is involved in the power to the relay. I finally found the alarm circuit and jumped that circuit at the alarm connector. Re-soldered the PCB and was good to go.

pete

 

it got a brand new fuel pressure regulator in 2019 so I doubt that’s the issue, however I will clean the ISV in the meantime for good practice.

 

No I haven’t. I have my reservations that the brand new DME from design911 was working..

I have my new pump prime relay coming and I am hopeful that will fix it. As when I prime it myself she starts first crack each and every time.

 

my car doesn’t cut out, maybe if I don’t give her enough rev taking off in first gear but that’s user error