Fuel Pressure Testing

[Richard BC]

I am about to check the fuel pressures on my '83 SC in order to try and identify some strange starting issues I have had for some time. My car has a WUR 089 which is not shown in the graphs in Bentley. It has a vacuum hose at the top and on the end.
What I could do with some help with is whether I follow the values set out for the 045 WUR and also which vacuum hose do I detach when doing the 'warm' control pressure?

 

[chas3.2]

Go to your OPC they will print of the page with all the vac & fuel pipes on.
Mite help.
Chas.

 

[BrianJ]

Or maybe this would help? https://assets-v2.porsche.com/gb/-/...s-Catalogue/PDF-EN-WW/KAT002_E_911_83_KATALOG

 

[Richard BC]

Thanks guys. If only it was that simple. I’ve now established that the 045 and 089 WUR’s are effectively interchangeable and the pressure readings are the same.
I just now need to confirm which vacuum line to remove when testing, the one that goes to the throttle body or to the thermo-switch (ie top one or end!)?

 

[richardstephens777]

Hi Richard,
what starting issues are you having? Is it warm start? When I did my WUR testing I left the vacuum and vent pipes connected. The Vacuum connection is for full throttle load which richens up the mixture.
The Vacuum operation can be tested using a hand Vacuum tool.. I have the figures if you need them.
Rich

 

[Richard BC]

Thanks Rich
The starting issue is very odd. Car starts straight away if it hasn’t been used for weeks and continues to fire up first turn thereafter unless it stands for an hour or so then it needs a while before it will start. Runs superbly when it does though.
The weird part is that it will be difficult to start up to 3 or 4 days after. If I leave it for a week, fires up first turn!
WUR rebuilt and calibrated by KMI, FA replaced, check valve replaced.
Should have done pressure checks first really but waiting for gauges to be delivered next week so will see how we go from there.
No one else seems to have had this issue. Normal hot start issues, yes, but not this delayed reaction business.
Richard B-C

 

[richardstephens777]

Hi Richard,
Sounds as though you might have a couple of issues. The standing for an hour sounds like a residual pressure issue. The primary pressure should be held above 35psi for at least 20 minutes.
Failure of this test can be caused by the fuel pump valve failure.
With the 3 or 4 day issue the cold start injector should start the engine. This is controlled by a thermo switch on the chain cover. Perhaps this is playing up.
Does it start and die or not start at all?
Rich

 

[T911UK]

Fuel accumulator would be my guess

 

[Richard BC]

Hi Richard,
Sounds as though you might have a couple of issues. The standing for an hour sounds like a residual pressure issue. The primary pressure should be held above 35psi for at least 20 minutes.
Failure of this test can be caused by the fuel pump valve failure.
With the 3 or 4 day issue the cold start injector should start the engine. This is controlled by a thermo switch on the chain cover. Perhaps this is playing up.
Does it start and die or not start at all?
Rich

 

[Richard BC]

Fuel accumulator has been replaced.
I tried to get the TTS out yesterday to test it but can’t shift it at the mo.
I’ll wait until I have my gauge to do a full fuel pressure test before further tinkering.
One other thing, I checked the voltage to the WUR and it is only 10.6v. It should be 11.5v min I believe. The battery is good and the voltage at the fuel pump relay is good. Not sure if the low voltage might affect the efficiency of the WUR?

 

[richardstephens777]

A resistance check of the WUR is a better test. It should be between 30 to 40 ohms.