| View previous topic :: View next topic |
| Author |
Message |
elitejaso
Joined: 24 Jul 2007
Posts: 143
Location: Melbourne
|
 Posted: Thu Apr 09, 2026 11:14 pm Post subject: New high pressure fuel pump but low system pressure |
 |
|
Hey Guys,
After a complete engine rebuild on my 81 S2 924 turbo and running the car it was idling rough and cutting out under acceleration.
Seemed lean so proceeded with fuel system pressure test and it was low at 4.5 Bar. Good range I believe is meant to be between 5.8-6.5 Bar.
Decided to replace the external fuel pump and in tank pump (as it was cooked) with a new 6.5 Bar external Bosch pump and strainer setup.
However with another test with the new setup still 4.5 Bar fuel system pressure. Ran a pressure test after the fuel filter and was getting 6.2 Bar, so up to the fuel distributor seems to be good.
Likely somethings up with the fuel distributor but not sure where to start, any ideas?
Would adjusting the pressure relief valve get me to 6 or so Bars from 4.5?
Thanks in advance
_________________
1981 924 turbo (daily driver) |
|
| Back to top |
|
 |
Cedric
Joined: 27 Aug 2004
Posts: 2801
Location: Sweden
|
| Posted: Thu Apr 09, 2026 11:38 pm Post subject: |
|
|
Maybe its time for a rebuild of the system pressure regulator, it sits in the fuel distributor and have some orings than can dry out, ball, spring and shims. Its very easy to take out and rebuild.
Dont run lean, you might put a whole in a piston, so be careful to put boost into it until its all sorted 
_________________
1980 924 Turbo
www.instagram.com/garagecedric/ |
|
| Back to top |
|
|
elitejaso
Joined: 24 Jul 2007
Posts: 143
Location: Melbourne
|
| Posted: Thu Apr 09, 2026 11:55 pm Post subject: |
|
|
cheers for the quick reply cecdric.
cool will get it rebuilt and see if that fixes it.
no boosting atm for me just really rough and crashing idle atm lol
_________________
1981 924 turbo (daily driver) |
|
| Back to top |
|
|
elitejaso
Joined: 24 Jul 2007
Posts: 143
Location: Melbourne
|
| Posted: Fri Apr 10, 2026 2:45 pm Post subject: |
|
|
Removed and inspected the system pressure regulator. Looks pretty good, o rings seem fine and no wear on the control piston. Had two shims installed.
Guess the spring could have weakened over time which might be the problem.
Is the spring included in rebuild kits?
Put it back in for the moment with a new copper washer which was .2mm thicker which has further dropped system pressure around .3 bar.
Can you adjust the screw plug out so the regulator sits further in hence increasing pressure?
Is there anything else that could be attributing towards my low s.pressure?
[/img]
_________________
1981 924 turbo (daily driver) |
|
| Back to top |
|
|
Cedric
Joined: 27 Aug 2004
Posts: 2801
Location: Sweden
|
| Posted: Fri Apr 10, 2026 5:14 pm Post subject: |
|
|
| elitejaso wrote: | Removed and inspected the system pressure regulator. Looks pretty good, o rings seem fine and no wear on the control piston. Had two shims installed.
Guess the spring could have weakened over time which might be the problem.
Is the spring included in rebuild kits?
Put it back in for the moment with a new copper washer which was .2mm thicker which has further dropped system pressure around .3 bar.
Can you adjust the screw plug out so the regulator sits further in hence increasing pressure?
Is there anything else that could be attributing towards my low s.pressure?
[/img] |
If i were in your case I would change all the seals first anyway to be sure Im not chasing or modding anything that i shouldnt and to be sure its as it should, before going on fiddling with more stuff. BTW whats the state of the fuel filter? Maybe could be worth it to double check the voltage at the fuel pump aswell when running.
Normally to fine tune system pressure you can add or remove the shims that you see when you pull out the pressure regulator. Though in your case your quite long way from the fine tuning range. I could measure the spring on a spare fuel head i have here sitting on the shelf aswell for comparison
I guess you know https://k-jet.biz/, an australian company ive heard knows their stuff, maybe they can sort out some seals. Just a quick 1750km drive to get there from Melbourne  Australia is friggin massive, That would be like me going from Stockholm to north of france, crossing a few countries on the way
_________________
1980 924 Turbo
www.instagram.com/garagecedric/ |
|
| Back to top |
|
|
924RACR
Joined: 29 Jul 2001
Posts: 9060
Location: Royal Oak, MI, USA
|
| Posted: Fri Apr 10, 2026 9:03 pm Post subject: |
|
|
| Cedric wrote: | | Just a quick 1750km drive to get there from Melbourne Australia is friggin massive, That would be like me going from Stockholm to north of france, crossing a few countries on the way |
Ha ha ha ha!!! Still closer than for me to drive to the Circuit of the Americas track in Texas! That's a cool 2220 km from The Motor City... and still only halfway across the States...
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype |
|
| Back to top |
|
|
morghen
Joined: 21 Jan 2005
Posts: 9095
Location: Romania
|
| Posted: Fri Apr 10, 2026 11:31 pm Post subject: |
|
|
If you csnt figure it out or just dont want to anymore, i sell an EFI conversion kit for these cars. The engine bay layout is kept and the parts are designed to look as close as possible to the originals. You even get a fuel distributor that looks very close to the original.
Check my website out: www.the924.com
_________________
Supercharger and EFI kits
https://www.the924.com |
|
| Back to top |
|
|
elitejaso
Joined: 24 Jul 2007
Posts: 143
Location: Melbourne
|
| Posted: Sat Apr 11, 2026 11:42 am Post subject: |
|
|
Looks like a neat kit Morghen, if I cant get it running will hit you up.
| Quote: | If i were in your case I would change all the seals first anyway to be sure Im not chasing or modding anything that i shouldnt and to be sure its as it should, before going on fiddling with more stuff. BTW whats the state of the fuel filter? Maybe could be worth it to double check the voltage at the fuel pump aswell when running.
Normally to fine tune system pressure you can add or remove the shims that you see when you pull out the pressure regulator. Though in your case your quite long way from the fine tuning range. I could measure the spring on a spare fuel head i have here sitting on the shelf aswell for comparison
I guess you know https://k-jet.biz/, an australian company ive heard knows their stuff, maybe they can sort out some seals. Just a quick 1750km drive to get there from Melbourne Australia is friggin massive, That would be like me going from Stockholm to north of france, crossing a few countries on the way |
New fuel filter from Porsche installed so should be all good. Also have tested the fuel pressure with the tester after the filter and it was showing a strong 6.2 Bar up to the fuel distributor so seems to be ok.
Gonna get a rebuild kit and replace the seals and what not as you've recommended and will take it from there. Cheers for the link to these local guys will check them out.
Yeah quite a drive done it once in a day do not recommend haha. Didnt have to cross multiple countries just two state lines. And if you want to drive to Cairns in Northern Queensland your basically double that.
| Quote: | | Ha ha ha ha!!! Still closer than for me to drive to the Circuit of the Americas track in Texas! That's a cool 2220 km from The Motor City... and still only halfway across the States... |
Might aswell just do the the cannon ball run 
_________________
1981 924 turbo (daily driver) |
|
| Back to top |
|
|
elitejaso
Joined: 24 Jul 2007
Posts: 143
Location: Melbourne
|
| Posted: Tue Apr 14, 2026 1:23 pm Post subject: |
|
|
| Quote: | | Normally to fine tune system pressure you can add or remove the shims that you see when you pull out the pressure regulator. Though in your case your quite long way from the fine tuning range. I could measure the spring on a spare fuel head i have here sitting on the shelf aswell for comparison |
Hey Cedric if you are able to measure that spring whenever you have a spare moment would be greatly appreciated
_________________
1981 924 turbo (daily driver) |
|
| Back to top |
|
|
|
FAQ
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
924 FAQ (Technical)
