Hi fellow 928-colleagues,

can perhaps someone point me to the right direction, as in which component could be the culprit for my warm start troubles :
1. I have a 928S euro of 1980, 4.7L 300Hp 3sp AT with K-Jet
2. cold start is no problem. Engine fires up right away without pressing throttle pedal
3. once engine is warm and I shut engine off, I can easily start after 5 to 10min, without pressing throttle pedal
4. however, when engine is warm and I shut it off for more than 30min, I cannot start the car again, not even when pressing pedal to the metal
I can hear engine wanting to start up but no luck. At the same time I can smell fuel at the exhaust.

Here is what I already did :
- check injectors : they are not leaking
- check system and control pressure when engine is cold and is not running : pressure within specifications
- I replaced diaphragm and seals of the WUR
- I replaced my ignition coil
- I replaced distributor rotor
- I replaced ignition leads
- I replaced my spark plugs
- I checked my emission value and it is 2% CO, so within specification of Porsche (between 1,5 and 2,5)

Is a bad WUR the culprit?
Or should I look for other failing components....

Here is a picture from one of my spark plugs :
https://cimg6.ibsrv.net/gimg/rennlis...3c6328008.jpeg

Then there are 2 things I can check:
- return valve fuel pump: easy to check : when engine is warm and before I try to start, I can jumper the fuel pump
to build up pressure again and then try to start. I can also measure pressure fall with a clamp on the fuel line at the
pump side.
- measure control and system pressure when engine is warm

That is indeed what I still need to do, I just am afraid of creating fuel leaks during tests with a gauge especially with a hot engine.

Btw I do not have a fuel accumulator, nor on this engine, nor on my old 4.5 240Hp engine
Before I swapped my 4.5l engine with this 4.7l engine,
everything worked. I never had starting issues.
Except from the ignition distributor, all CIS components are the same.
So I reused them on my newly rebuilt 4.7l engine.

Dear Allan,
when I have a problem with my return valve of the fuel pump, shouldn't this also occur at cold start?
I will try to eliminate the return valve issue first by putting a clamp on the fuel line near my fuel pump
If fuel pressure still drops, the problem is my fuel distributor.

However, I still suspect my WUR as I needed to knock the pin (where bimetallic coil is attached to) further into the WUR as
my control pressure at cold was too high(3,5bar instead of 1,3) and thus I could not start the car as I got too much fuel when starting.

but of course this will also influence my pressure when warm, not?

Hi Alan,

now I know what you mean. Is there a rebuilt kit with the O-ring so that I can replace mine just to eliminate faults on the relieve valve?

I speak fluently French As I am working in Brussels, but my technical language in French is not so good.