rtbehm

My 964 turns-over for about 8-10 seconds before starting. My mechanic says its due to low fuel pressure. We've changed the spark plugs, distrubutor cap and rotor, injectors, fuel filter, check valve on fuel pump, cylinder head temp sensor.

Any other recommendations to cure this issue?

cjoenck

Yes, there is a fuel pressure regulator valve behind/underneath the throttle body. It is vacuum operated and the issue could be as simple as a bad vacuum line. They do have a diaphragm inside that can go bad from heat and age. The part number is

928 110 198 04

It is part 17 in the picture attached. You can replace this with the engine in the car.

Geoffrey

Well, it is not exactly vacuum operated. The fuel pressure regulator is operated via a spring internally and then referenced to the manifold pressure. This is to maintain the same differential pressure at the tip of the fuel injector.

rtbehm

Thank you all for the great information!

Regards,

RT Behm

cjoenck

I stand corrected. Yes, I was a little sloppy in my comment. I guess I meant to say that a "simple" vacuum issue (if there is such a thing) can have impact the operation of the pressure regulator. I was trying to say that the regulator may not be defective but could be. Enough said, thanks.

Laker

I believe there is another fuel filter inside the tank, which is a b*tch to get to.

Indycam

If you do a dme relay jumper will it start right up ?

SeanR

Those FPRs or fuel dampeners have a vacuum diaphragm inside, if they are leaking they can allow fuel to enter the vacuum lines. Take one of the lines off and give it a sniff, this will tell you if it's leaking and that is where your fuel pressure is going.

PorscheDoc

Vacuum lines are in good shape, DME relay is good. FPR is bleeding off when vacuum is put to it.

Indycam

I didn't ask if the dme relay was good or bad . I was thinking that if you started up the fuel pump with the dme relay jumper , let the fuel pump run and then turned the motor over ...
The fuel pressure would be there because the pump had pumped up the lines .

Goughary

My car does the same thing. So I'm listening to hear the solution...

Was thinking maybe to order the fuel pressure regulator to try out. Anyone know what one costs?

Marc Shaw

$166.75 from Pelican.

I ordered one about a week ago as PM (and cause it is a bugger to get to and my intake is off right now so seemed like a good time to do this).

Marc