Pizza

I installed a fuel pressure gauge on my car last night. When I turned the key on I got no pressure at all. When I cranked up the car the gauge was only reading 10 psi at idle. I know it should read 29 psi. Any suggestions on where to start troubleshooting.

Thanks

Jim bailey - 928 International

Try pinching off the fuel return line to see if the pressure rises. If it does then most likely the fuel pressure regulator 928 110 198 01 at the rear of the passenger side fuel rail has failed.

borland

There is also a test fitting at the fuel pump. Since the regulator regulates pressure at the fuel rails (10 psi in your case), if you can install the gage at the pump test fitting, you can see the pump pressure with the engine running.

If you find enough pressure at the pump, that would rule out a bad pump and point to the regulator as being defective.

Where can I buy a gage with the proper metric fitting/adapter?

borland
90' S4, Slate Metallic

figgen

I'll echo Borland's question

Where did you get the gauge and fitting??

TAREK

So you can remove the cap nut and screw in the gauge in there? cool! (there might be a metal fuel line in the way though. Might want to consider one of those fuel pressure testers with rubber lines and various adapters)

TAREK

Also before you go crazy over your car... what are the chances that the guage itself is defective?

Pizza

Thanks Jim, I will try that test ASAP.

Thanks borland, I will try to rig up something and try that test too ASAP.

I just drilled and tapped the test port cap and installed a SS gauge.

Thanks Tarek, I will test the gauge on FeedNfrenZ's car if he lets me.

borland

So you drilled and tapped the test port cap. On the S4, the fuel rail cap is installed with a ball to make the seal. So that wouldn't work without a ball with a hole thru it?

Apparently the easiest way to adapt the gage is to use 7/16" I.D. rubber hose and hose clamps over the test port. The S4/GT/GTS test port is threaded 12mm x 1.5mm male, so the O.D. is slightly under 1/2".

The Actron fuel pressure gage for Schrader valve cars (about $40 at PepBoys) accomodates a 37 degree flare fitting. So some combination of adapters and hose barb, length of hose, hose clamps, will do the job. Leak test before running the engine with a jumper at the fuel pump relay socket.

borland
90' S4, Slate Metallic

TAREK

Nope. and it's a pain to seal, but it can be done.