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Might be a new 924 owner, need help

 
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RyanCooper  



Joined: 16 Aug 2018
Posts: 3
Location: Texas, United States

PostPosted: Thu Aug 16, 2018 7:24 am    Post subject: Might be a new 924 owner, need help Reply with quote

So I found this 1977 Porsche 924 on craigslist and I was wanting to trade my 84 300D for it, the guy is interested but the following is stumping him and me: good old CIS injection issues were thought to be the cause of the car starting and running for about 4 seconds and then dying and not restarting until waiting about 10 minutes. He replaced the fuel distributor, warm up regulator, fuel pump, some fuel lines, the injectors spray evenly, new timing belt, dizzy, spark plugs, and was timed correctly and firing order is correct.

He said it was running fine and one day he went to start it up to let it idle and it started doing this. Could it be flooding somehow? If so how do you fix this, or what else could be the issue?? He did a compression test and got 135ish psi per cylinder, is this too low? Could it be a leaking head gasket? I really love this car and want to get it but don't know what the issue is..[/b]
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Ian89C4  



Joined: 01 Apr 2011
Posts: 539
Location: North Carolina

PostPosted: Thu Aug 16, 2018 1:17 pm    Post subject: Reply with quote

Welcome!

I would get a cis pressure tester on there ( or at least the current owner) and that will tell you what the issue is. Very hard to diagnose a cis without a bead on what the three required pressures are. It sounds to me like that although there is enough pressure to open the injectors, once the cold start injector turns off, there isn't enough fuel being sprayed in. By lifting up the plenum to check the spray on the injectors you are artificially creating an air flow. In reality the actual airflow may not be enough to open the injectors at idle.

Get a cis pressure tester and get the operating and cold pressures and then we can see where to go from here there.

Good luck!
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Ian Edgerly
Spiveys Corner, North Carolina

Current:
1981 924 Weissach Race Car ("Serenity")
1980ish 931 ("Alice")
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RyanCooper  



Joined: 16 Aug 2018
Posts: 3
Location: Texas, United States

PostPosted: Sat Aug 18, 2018 6:48 am    Post subject: Reply with quote

Ian89C4 wrote:
Welcome!

I would get a cis pressure tester on there ( or at least the current owner) and that will tell you what the issue is. Very hard to diagnose a cis without a bead on what the three required pressures are. It sounds to me like that although there is enough pressure to open the injectors, once the cold start injector turns off, there isn't enough fuel being sprayed in. By lifting up the plenum to check the spray on the injectors you are artificially creating an air flow. In reality the actual airflow may not be enough to open the injectors at idle.

Get a cis pressure tester and get the operating and cold pressures and then we can see where to go from here there.

Good luck!


Well turns out he's actually made a thread here about it and was told the same thing. He doesn't wanna buy the tester because it's expensive and he belives the Fuel Accumulator to be bad as its leaking and to his and my knowledge that controls fuel pressure/flow for cold starts which it obviously can't do, he's replaced literally everything else besides that and the injectors which again spray evenly. Id say it's and good bet the accumulator/regulator is the culprit. Are he and I the only ones that think so? ("He" = seller/current owner)
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Ozzie  



Joined: 12 Mar 2005
Posts: 4416
Location: Townsville, Qld. Australia

PostPosted: Sat Aug 18, 2018 9:43 am    Post subject: Reply with quote

The fuel accumulator doesnt control pressure. It smooths out the pulses in pressure from the fuel pump and holds the system pressure after shutdown.
If leaking it needs replacing anyway.

System Pressure is controlled by the regulator in the CIS.
The WUR manages the Control pressure for cold starts and for normal running the CIS adjusts it via the flap (vacuum from TB)

System pressure can be adjusted by shims in the CIS regulator
The CIS also has an adjustment via allen key for adjusting fuel mixture.

Learning about the CIS and pressures will help with diagnosis.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance
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RyanCooper  



Joined: 16 Aug 2018
Posts: 3
Location: Texas, United States

PostPosted: Sat Aug 18, 2018 9:50 am    Post subject: Reply with quote

I would definitely check those out, but do you think it could just be weak vacuum/leak or be the regulator in the CIS or mixture that would cause it to have those symptoms?

I kinda just find it hard to justify buying a pricey pressure tester when I could just use normal engine diagnosis to figure out if it's too low of pressure or diagnose what is typically known to cause these issues.

Not trying to be ignorant just saying... I'll see what he says and check back
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Paul  



Joined: 02 Nov 2002
Posts: 9348
Location: Southeast Wisconsin

PostPosted: Sat Aug 18, 2018 12:20 pm    Post subject: Reply with quote

If you insist at throwing parts at this issue, replace these:

Fuel pump relay
Ignition switch
Ignition coil
_________________
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
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Ozzie  



Joined: 12 Mar 2005
Posts: 4416
Location: Townsville, Qld. Australia

PostPosted: Sun Aug 19, 2018 4:26 pm    Post subject: Reply with quote

check ebay, seen test kits as low as $30
While you are at get a Haynes car manual

I think there is a write up here on how to build your own tester cheaply as well.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance
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