924Board.org

[malpaslane]

I,m having another fuel pressure problem, after getting car up and running after four year layup, i,ve taken it to a garage to have the timing and mixture done and they,re now telling me that there,s something wrong with the fuel pressure, i,ve got other posts on here about the fuel relay and fuel filter,but i think they are now sorted. The garage are saying that the pressure was around 130 psi and they,ve manage to get it down to 90psi (not sure how they,ve done it) and are saying it should be more like 80psi ,is this right?, they say that they can,t set the mixture and timing because the pressure is going up and down to much to set it, which can understand, i,ve put a new pump,relay, wur and filter on , but the filter i was supplied was also listed for a 944, which i think is wrong and have another one coming from porsche, could this be the problem or is it something else. The car it self drives ok, but idle was high at about 1000 to 1200 warming up and when it gets hot (temp gauge to half way ) it idles at 950, but it will only get to half if i,m sat in traffic. Any help would be great, so i can her back from the garage to drive (it,s been blood sweat and tears all the way with this one).....
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931 1982, PAIN IN THE ARSE,BUT GETTING THERE. 911 1976 2.7. 931 1981 S2(NON RUNNER) ALFA 156 SPORTSWAGON.

[crow.magnum]

im having the same problem with mine any sugestions anyone

[Rasta Monsta]

Primary pressure regulator?
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Toofah King Bad

• WeiBe (1987 924S 2.5t) - 931 S3

[-nick]

You can adjust the pressure some by using shims in the regulator part of the fuel dizzy. Which is probably what they did. Check the direction of the fuel filter first off. If the pressure is fluctuating then it sounds like an issue with the pump or the power to it.
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1980 931S
15psi boost, MS-II, EDIS, 951 IC, custom intake, Ford 5.0L throttle body, Forge BOV, WB o2, G31 w/LSD, 964 wheels, 968 rear sway, Bilsteins, 200# Welt. springs. A laptop, and a partridge in a pear tree.
1991 964 C4 Cabriolet

[RC]

Why won`t the main pressure go lower? Adding shims will raise pressure and removing the 2 fitted should lower it providing the correct size O ring is installed. Does the valve piston slide easily?

Possibly may have a blockage in the return line then.

Roger

[malpaslane]

Hi All, the garage did adjust the shims in the primary pressure reg to get the pressure down, there may still be a problem with that as before i took it to the garage, when i was getting the car running i may have mixed up the piston or just the spring and valve behind the piston from another metering unit i have, so we,re trying the other piston and parts on car to see if that makes a difference,the o rings could be the problem there also, as when i first the took piston out there was only one o ring on it so took an o ring from another piston, so again this could be where the problem is, could the o rings be old and need replacing?, there,s no blockages in return line as that was one of the first things i checked when the car wouldn,t start, I have another post about the fuel relay burning out on here, which some members think could be to do with low voltage, because i have had low voltage readings from the alternator, which started to happen not long after car was up and running, so we,re looking at that to and i,ve bought a genuine porsche fuel filter now as over here in the uk most filter makers list the 924 turbo filter the same as a 944 , so we,ll see what difference that makes as well. many thanks Rik
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931 1982, PAIN IN THE ARSE,BUT GETTING THERE. 911 1976 2.7. 931 1981 S2(NON RUNNER) ALFA 156 SPORTSWAGON.

[malpaslane]

Hi All, Ok so i went and got the car back from the garage on the weekend, to see if i could find out what the fuel pressure problem was , armed with all my knowledge from you guys. I first changed the filter for the porsche one and took off the 944 one, they look the same,but who knows what the difference is, then i took the pressure reg piston out of the head and found that the two shims behind the spring were the same size 0.25mm, i,ve got another fuel head ,so i took the pressure piston out of that one and found that the shims were 0.47mm and 0.07 mm, i,m sure i,ve read somewhere that the shims should be about 0.20 something and a thin one around 0.07, so i put those two in and the the pressure came down, i also changed the seal on the end of the piston as i had fitted one from work and it looked a to thick, now the pressure is about 88 - 90 psi, which has come down from 130 psi. Just to check after i had changed the seal i put the old shims back in and the pressure went back up to 95 psi, so i think the shims were wrong,but the seal was the biggest problem. All this took me 10 mins, the garage had the car 2 weeks , perhaps all garages who work with porsches should sign up to 924.ORG. Many thanks for all the help Rik.....
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931 1982, PAIN IN THE ARSE,BUT GETTING THERE. 911 1976 2.7. 931 1981 S2(NON RUNNER) ALFA 156 SPORTSWAGON.

[924RACR]

So true... sad, but this car seems to be a completely mystery to so many "expert" Porsche garages...

It's not like it's the only CIS car Porsche or VW ever made!!!
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[jp928]

Fwiw, to properly diagnose CIS you need a gauge set so you can see whats happening - $60 at JC WHitney. Also get Ben Watson book on Bosch injection (Amazon, $15), really good part on CIS, and its diagnosis, pressure problems, the works.
jp