Fuel pressure readings

86porsche · 08-08-2009, 10:21 AM

Hi Lads, my car is an 86 16v euro spec model.

I'm having an issue with my car hard starting, after I take it for a run and letting it cool down for 10min or more It takes a good 10 secs to start again and I have to pump the pedal a few times, starts first time every-time other then that.

So I hooked up a gauge to the fuel test point and got these readings.

Started her up and the gauge read 6bar about 90psi it was jumping around abit.

shut it down read 2.5 bar about 36psi

20 min later 2.0bar about 30psi

1hr later 1bar 15psi

I also did the test while bridging the fuel pump.

Got 6bar again 90psi and held pressure from 2.5bar to 1.5 for 20mins 0 after 30min

ran the fuel pump also to check output got 1600cc for 30 sec.

can someone please tell me are these reading ok? Need to fix this problem so any other ideas are appreciated?

zoltan944 · 08-08-2009, 02:12 PM

Hmmm, I don't know the Euro readings, but unless the euro needs 3 times the fuel pressure there is something wrong!
All OBs (at least not euro) are in the range of 30psi running and 36ish psi with the vacuum pulled, presure should be steady for 20min and GONE within an hour. I beleive you have a problem and this would make sense if this is correct:
cold car needs more fuel, starts up with the extra fuel. Car is hot, too much fuel doesn't want to start.
You should NOT press the petal to start the car, the timing can change drastically and cause negative things like backfires and such

86porsche · 08-10-2009, 05:44 AM

ok. I was thinking that my pressure was way above what it is ment to be. Im guessing the gauge was ok as I bought it new.

So that leads me to my next question. What would cause having such high pressure? The needle was also jumping around quiet abit 85-95psi. this could effect my fuel consumption also?need to fix this!anyone?

Danglerb · 08-10-2009, 10:07 AM

The workshop manual will have the test values for pressure, but off hand pressure too high sounds to me like a bad pressure regulator. Pull off the vacuum hose and see if it smells like fuel, ie leaking diaphragm.

Pumping the pedal, or holding it down is what I have heard you do for a flooded, too much fuel, condition on the 928.

928forlife · 08-11-2009, 05:02 AM

Quote:

Originally Posted by Danglerb

The workshop manual will have the test values for pressure, but off hand pressure too high sounds to me like a bad pressure regulator. Pull off the vacuum hose and see if it smells like fuel, ie leaking diaphragm.

Pumping the pedal, or holding it down is what I have heard you do for a flooded, too much fuel, condition on the 928.

I have an 85 euro, your 6 bar figure is way too high. Fuel injected engine should never need the gas pedal pressed at all.
Just turn the key and it should start.

86porsche · 08-11-2009, 11:25 AM

ya Im trying to pin down the exact cause. Going to take danglerbs advice and start looking at the fpr. Thanks for the input lads going to start investigating. oh and just as a precaution what are the side effects of running the car for a while with pressure that high? dont want to cause damage!!

Danglerb · 08-11-2009, 02:34 PM

High pressure, way too rich, I wouldn't drive it.

Bust a hose or something, not too likely, rating is like double that pressure.

Gas wetting the cylinder walls, washes down the oil, LOTS of wear.

Gas leaking through the vacuum system, hard to predict.