924Board.org

possu · Joined: 29 Dec 2003 Posts: 7

Hi. I have a problem to start when my car have been stand by a while it doesnt run.
I have solved a problem by putting a button(12volt) in cold start valve that i can open that manualy it s working but i want to fix that properly, any hints how i solve my problem?

BTW.Sorry my bad english"

Roger · Joined: 06 Jan 2003 Posts: 1235 Location: Cordova, TN

What year and model?
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1981 924 NA

Some people are like Slinkies. Not really good for anything, but you
still can't help but smile when you see one tumble down the stairs.

possu · Joined: 29 Dec 2003 Posts: 7

-78 924 its in topic.

dpw928 · Joined: 02 Nov 2002 Posts: 1860 Location: owasso, ok 74055

Possu,

The cold start valve is only supposed to work when the engine/water temp is less than approx 100 F. If it doesn't work at that temp, the thermotime switch is bad. If you have a problem at warmer temps the probable problem is in the warm up regulator or your air/fuel adjustment.

Dennis
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81 931 5 sp
78 928 5 sp Silver
78 928 AT Euro Black

Lizard · Posted: Tue Dec 30, 2003 6:03 am Post subject:

There is a constant 12 volts which runs to the thermo time switch on the back of the head, this then flows through the switch ove to the cold start valve, the +12 volts which runs to the thermo time switch is fed by the fuel pump relay/power system, check to see if you have power at the thermo time switc if yes then the thermo time switch is bad, if no then you have to trace the wires and find out where the power break is
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3 928s,

CMXXXI · Joined: 05 Nov 2002 Posts: 1939 Location: Vicksburg, MS

Don't overlook the check-valve at the fuel pump and the accumulators. Between them, they are always warm start problem culprits.
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'79 Eurospec 931

dpw928 · Joined: 02 Nov 2002 Posts: 1860 Location: owasso, ok 74055

CMXXXI,

Knew I was forgetting something. Good catch. They say the memory is the second thing to go when you get old. Think I'm in trouble.

Dennis
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81 931 5 sp
78 928 5 sp Silver
78 928 AT Euro Black

possu · Joined: 29 Dec 2003 Posts: 7

Thanks.
Can i broke something with my modification in cold start valve?
When i give 12 volts manualy to that.

Roger · Joined: 06 Jan 2003 Posts: 1235 Location: Cordova, TN

Sorry I missed the year and model in the subject. Porsche went to a single 40cc accumulator in 79 ir 80, and the check valve on fuel pump. That was the factory solution to the warm start problem. I belive that you have two 20cc accumulators. Your modification to the cold start valve has been done many times and you wont damage anything.
_________________
1981 924 NA

Some people are like Slinkies. Not really good for anything, but you
still can't help but smile when you see one tumble down the stairs.

numbbers · Posted: Tue Dec 30, 2003 11:19 am Post subject:

Possu, I don't think you could have broke anything. The thermo-time switch supplies ground to the cold start valve. Putting a constant 12V on the valve will not do anything once the thermo-time switch has opened. The hot start problem is caused by the thermo-time switch timing out too soon. Even under hot conditions the thermo-time switch supplies ground to the cold start valve for approximately three seconds. This give a shot of extra fuel to the mixture for starting. The problem is that three seconds of extra fuel is not always adequate for an old engine where everything is not up to snuff.

The hot start problem mod that I wrote for the tech section allows you to override the thermo-time switch to get your car started.
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1980 924 Turbo

Paul · Posted: Tue Dec 30, 2003 11:30 am Post subject:

This problem is caused when the car sits after being run and the heat in the engine compartment causes the fuel in the lines to boil. Its the classic vapor lock that has been a problem for decades in many cars. In our cars, Porsche has tried to reduce this problem by running a radiator fan after shutdown and by trying to keep pressure in the lines (causes the fuel to boil at an higher temp).

The solution is to run the fuel pump long enough to purge the lines of vapor.