Kevin in Atlanta

1990 S4 105k recently resurrected (second time) after sitting for years in NC. Gas tank is 3/4 with fresh gas put in there last year.

Last night:
Cold start fuel pressure good (55ish as needle bounces) and will start. Hot little or no fuel pressure and non start. Pushed it into the garage.

Today:
Doing diagnosis. Car was cold. Checking continuity at the FP fuse. At first no continuity, but seemed to flicker when I cranked her and fuel pressure built up and car started.

Drove approximately 4 miles in my subdivision. Ran ok but seemed down on power. Park it in front of my garage, turn it off and immediately try to restart it - would not restart. No fuel pressure.

Diagnosis:
Key on hot no continuity at fuel pump fuse (#38). Pulled fuse and it is very warm. Would like to avoid melted CE panel.

Ordered a new fuel pump just in case this one is giving up the ghost.

While I wait for the new fuel pump I'm going to replace the fuel pump relay.

How do I measure the amperage it the fuel pump is drawing? (newbie)

Also replaced the fuel regulator with new one earlier today- fuel pressure was dropping to 0 as soon as the engine stopped. Checked the regulator and it was full of gas.

Any additional guidance? Anything i have not considered?

John Speake

Changing the relay is a good idea. You probably know that the fuel pump and also the O2 sensor are powered by that relay and fuse.

If you disconnect the O2 sensor then pull the fuse, and connect your multimeter on 10A range across the fuse terminals you can measure the FP current draw.

Speedtoys

Should have started with measuring voltage drop down the electrical path.

Might have a lose fuel pump fuse holder...ive had that.

The heat is resistance..find it, could save you $ in parts thrown at the car.

Kevin in Atlanta

So, tried to start it - and with the key on no continuity either side of fuse. Try to start the car no continuity - but when I release the key I have continuity. Some fuel pressure is building up. Time to pull the computers so I can get to dadgum relay that Porsche managed to hide back there.

Kevin in Atlanta

There you go - replaced what appears to be an original relay with a new - same test - different result - it starts up immediately after running about in the neighborhood.

Continuity test post new relay was different. No continuity until it starts and then it stays on. Wierd. Going to double check that finding. And going to replace all the 53 relays.

John Speake

Remember that the FP is not energised until the engine is turning.

928S MN

I just replaced all the 53 Relays in my CE panel because after 31 years it's cheap insurance. What is this one behind the computers you speak of?

I have a 85MY 5 spd.

Kevin in Atlanta

On the 90 and up maybe earlier, the FP relay is the last one on the top right. Right behind the computers.