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Ozzie · Posted: Fri Oct 27, 2006 8:40 am Post subject: Hot Start Fix?

Going through a few ideas for fixing my hot start problem and wondering why a fuel pressure regulator cannot be fitted the fuel return line.
It appears that the one built into my fuel dizzy doesn't work as everything else is fine.
I'm looking at this one.
http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&ih=001&item=110047148737&rd=1&sspagename=STRK%3AMEWA%3AIT&rd=1
Comments anyone?
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

Ozzie · Posted: Fri Oct 27, 2006 2:12 pm Post subject:

I'd be setting the return line to 20-25psi and see what effect is has on the WUR and I wont be connecting a vaccum line at first.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

Mike924 · Joined: 12 Aug 2004 Posts: 2601 Location: IoW UK

I don't see how it would help, Ozzie.

All the regulator would do is maintain the pressure between the regulator and the tank. It would do this by bleeding excess pressure back to ...er... the tank.

It could only do this if the back pressure was over 25 psi (say 30) anyway. Once this pressure drops to below 25 the output pressure from the regulator would drop too.

Besides, wouldn't the system pressure regulator close off the return line if there's no pressure from the pump?

I may have misinterpretted what you're trying to do.
_________________
1985 Porsche 924 'Lux', Kalahari Beige (my ex)
1993 Porsche 968 Coupe, Midnight Blue, 6 spd

'There is no substitute for a little grease under your fingernails.' - Chrenan, 924board.org

Ozzie · Posted: Fri Oct 27, 2006 5:32 pm Post subject:

I believe the pressure regulator in the fuel Dist is fubar and leaks back to tank after shutdown and parts are not available to repair.
AAV and WUR appear to work fine but I still have a hot start problem.
I plan to put a pressure regulator in the fuel return line that will keep the pressure at a minimum of 25psi (about 1.7bar).
This will keep the system from the pump through to the regulator at 25 psi and prevent vapor lock (after shutdown)
When the motor is running the fuel dissy will operate as normal. (in theory)
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

Mike924 · Joined: 12 Aug 2004 Posts: 2601 Location: IoW UK

Mike924 · Joined: 12 Aug 2004 Posts: 2601 Location: IoW UK

If you're sure that your fuel dist regulator is completely U/S, what you can do is put your new regulator in the line between the filter and the dist, and set it to 70 psi, effectively replacing the function of the fuel dist reg. Block off the return port from the fuel dist (not sure how to do this) and feed your return line from the new regulator.

Should work in theory, but I can't picture the circuit in enough detail to be sure if it will work in practice.
_________________
1985 Porsche 924 'Lux', Kalahari Beige (my ex)
1993 Porsche 968 Coupe, Midnight Blue, 6 spd

'There is no substitute for a little grease under your fingernails.' - Chrenan, 924board.org

Ozzie · Posted: Fri Oct 27, 2006 10:46 pm Post subject:

The fuel pressure regulator in the dist has two functions.
1 maintain system pressure when running at 4.5 to 5.2 bar and drains excess to tank.
2 maintain pressure when shutdown at 1.5 to 1.7 bar by shutting off the drain.
It does the 1st one just fine.
After shutdown any pressure above 1.7 usually drains to tank and then it should shut off. This it doesn't do.

The accumulator is like a balloon which pressurises when the pump is running. When the pump shuts down the accumulator will maintain pressure in the lines if there is no leaks. Mine is leaking past the pressure regulator.
If you look at page 73 of the Haynes and look at item 13 in the picture you' get an idea of the CIS. I am thinking of putting a regulator between 13 and 15.
From this diagram if you blocked off the fuel return line you would get pressures well above 25psi.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

Ozzie · Posted: Fri Oct 27, 2006 11:00 pm Post subject:

Another option I was looking at was an electric shutoff solenoid that would shutoff with the fuel pump.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

Mike924 · Joined: 12 Aug 2004 Posts: 2601 Location: IoW UK

That would work much better. If fact, because it's effectively instant, it might keep the pressure up well above 1.7 bar. Again, it all depends on how good your accumulator is.
_________________
1985 Porsche 924 'Lux', Kalahari Beige (my ex)
1993 Porsche 968 Coupe, Midnight Blue, 6 spd

'There is no substitute for a little grease under your fingernails.' - Chrenan, 924board.org

Smoothie · Posted: Sat Oct 28, 2006 1:57 am Post subject:

Why not just replace the o-ring seals in the fuel dist's pressure regulator? Should be one, or in the case of later versions with the WUR return check valve, two o-rings as in this diagram - http://pg.photos.yahoo.com/ph/smoothies931pics/detail?.dir=341f&.dnm=3e72.jpg&.src=ph
_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

Mike924 · Joined: 12 Aug 2004 Posts: 2601 Location: IoW UK

Ozzie · Posted: Sat Oct 28, 2006 7:24 am Post subject:

In Smoothies pic it shows the return from the WUR going throught the regulator.
Mine does not do that. Maybe Lambda?
No kit available for the NA.
The 'o' ring option would be cheaper.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

Ozzie · Posted: Sat Oct 28, 2006 9:52 am Post subject:

Decided to pull out the regulator and check the seal etc.
This is what I found

No shims and the seal is hard so I'll see about getting these from the dealer on Monday.
Pelican has them but I'll have to import from the USA.
Might solve a few problems.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

Paul · Posted: Sat Oct 28, 2006 10:04 am Post subject:

New info in next post...
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

Paul · Posted: Sat Oct 28, 2006 10:21 am Post subject:

I bought these to fix mine:

http://www.specialtauto.com/Merchant2/merchant.mvc?Session_ID=b93da62daaec7d6ac29e08870baa78d4&Screen=PROD&Product_Code=30198

_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.