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Join Date: Jun 2018
Location: Brittany, France
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Fuel Pressure Regulator - faulty?

Hi everyone...

In tracking down my poor performance issues.....just trying to eliminate possible faulty parts.

So, my fuel pressure checks out as per Clarks under the various conditions. The only thing I have not done it physically drive it with it stuck to windscreen......anyhows, I don't have a non start issue but when I pulled the small vac hose from the FPR it smelled of petrol. There where no drips of petrol coming out and checked for about 5 mins with engine running and vac hose off and still no drips. However, it really does smell of petrol when you take it off.

Is this normal? If not, any way to test it?

Thanks,

M
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Old 08-30-2018, 10:37 PM
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If it were leaking enough fuel to cause poor running the plugs would show signs and it should also produce black smoke or at least smell rich when sitting at idle. At idle your vacuum should be quite high and that'd be when the most fuel would get sucked through the failing regulator into the vacuum system.

You could use a hand pump and the vacuum brake bleeder can that often comes with it to see if you can pull some fuel out, try it with the system under pressure for maximum pressure delta to vacuum.

I'll smell-test my regulator in a bit. -Joel.
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Old 08-31-2018, 04:42 AM
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OK just checked and I can not-really smell fuel at the regulator vacuum line. One sniff produced a very faint fuel smell but really it was insignificant. Of course the other end of this hose is connected to the intake which can smell of fuel a bit. This was a vague suggestion of a fuel smell and of no concern.

If you have a stronger smell it might be coming from elsewhere, a dripping injector or maybe just bad luck with an injector firing after the ignition was shut down at key-off.

If you disconnect one injector does it run better?
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1987 928S4
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1994 968 cabrio - Supercharged
Old 08-31-2018, 04:53 AM
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The damper diaphragm could be bad and cause fuel to get pulled in through the vacuum line into the throttle body.
Old 08-31-2018, 12:35 PM
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Quote:
Originally Posted by djnolan View Post
The damper diaphragm could be bad and cause fuel to get pulled in through the vacuum line into the throttle body.
Easy check. Pull the vacuum line of the damper and see if it leaks fuel. If it does itís bad which means itís dumping raw fuel directly into the intake!
Look closely you can see a drip of gas from the vacuum line. This was on my S2.
Old 08-31-2018, 04:18 PM
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^^ This is good advice. Had the same problem with my 944T and its FPD. Some other symptoms are slow loss of fuel pressure and lazy/slow starts. Also wrote up a little except about it on my blog. Bad news for the 944 crowd is that OEM FPD is currently NLA jacking the prices through the roof of any left around.
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Old 09-01-2018, 04:23 AM
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as the OP said "There where no drips of petrol coming out and checked for about 5 mins with engine running and vac hose off and still no drips. However, it really does smell of petrol when you take it off. "
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Old 09-02-2018, 03:20 AM
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M, you need to measure actual fuel pressure in rail.

One reading at idle with vacuum hose connected.
Another reading with it disconnected.

Also measure voltage output of AFM as you manually move flapper door through its entire range of motion. What is minimum voltage with door closed. What is max voltage with door fully open? Does voltage increase smoothly with no dropouts along way?

Disassemble entire intake from AFM to intake-valves and replace all gaskets and clamps

Last edited by DannoXYZ; 09-03-2018 at 08:46 AM..
Old 09-03-2018, 04:14 AM
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