924Board.org

Candayanday · Joined: 11 Jul 2003 Posts: 2

Hi

I have had my 1980 2.0 924 for over 3 years, but have never properly had it on the road.

Due to previous problems with corrosion in the fuel tank, over the past 18 months, I have replaced tank, pumps, metering heads, fuel lines, idle valves, u name it.

However, It's current problem, and I hope last, is that it wont start when hot.

I was very happy when I found this article: http://www.924.org/techsection/hot_start_problem_fix.htm

as I thought my problems were solved. I had never replaced the injectors and I thought this must be it. It hasnt fixed the problem.

I understand that there is a kit that I can fit. What parts do you reccommend I use?

Has anyone here done this?

Many, many thanks.....

Andy
(In Sunny North Yorkshire)

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

Andy,

One simple test is to pull the connector off the cold start valve when you have the hot no start. If it starts, the thermotime switch is bad. If that doesn't work try cycling the key on and off a few times before cranking. If that works you probably have a bad check valve on or in your fuel pump. If that doesn't work hold the accelerator all the way to the floor and try starting it. If it starts after a few cranks there is a fuel leakdown into the intake. Since you have replaced the injectors, the leak is probably in the cold start injector or the fuel distributor is leaking.

Good luck,

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

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

I am not sure which year Porsche made the change but it is my understanding that on later models Porsche added a check valve to the fuel pump and went from a two 20 cc fuel accumulators to a single 40 cc fuel accumulator. I am not sure what you have on your 1980, but even if you have the single accumulator it could be malfunctioning. In the bottom of the accumulator there is a screw. Remove the screw and if fuel leaks out then you might want to replace the accumulator. I would also recomend a CIS pressure test.
_________________
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.

positivesale · Joined: 12 Nov 2002 Posts: 126

The check valves in these pumps are near impossible to replace, without nicking up the little holder that holds it in place. I cannot find a source for the check valve - dealer doesn't sell them. There is a little weird rubber thing, a weird washer/holder, a spring, and I think that's it.

However, it seems to be a common misdiagnosis. I had two fuel pumps on with two good check valves doing a test on a 931. It still didn't start when hot. I believe the problem was the warm up regulator, but I never really got a chance to find out what the problem was. Also, leaky fuel injectors (do you smell gas in your oil after the car has sat?) could cause some problems.

Just a thought.. maybe leaky injectors encourage air to get inside the fuel lines.. because of less pressure.If air has room to move, maybe the air can form bubbles easier (as opposed to when under pressure!). SO with leaky injectors, AND a bad chack valve, that would make things even worse (even less pressure).

I do have a 82 931 that starts when its very hot in all conditions. Today it was 30 degrees celsius. The car sat in the sun and was hot for a few hours after running. I started it right up when I came to the car with no problems. Cold start is superb too - it's instant gratification when it's freezing cold out and baking hot out.

One other problem that really affects hot starting, is a leaky exhaust manifold or gasket(s). Why? it causes more heat under the hood, and also screws up the fuel mixture. The mixture is inconsistent. this also encourages leaky injectors, because when you have a leaky exhaust manifold, the fuel mixture setting has to be set richer. When the fuel mixture is set richer, the injectors will spray fuel even when the car is turned off (for a few seconds.. also causes backfire after turned off). When the fuel pump primes in "key position 2" for that split second, you also get leak there if the mixture is set too rich. More gas in the oil, all because of a bad leaky exhaust system.

I do think that the quick fix cold start injector kit is not the way to go long term, since it's a hassle.. unless you are on a budget or need a temporary fix. Because these cars CAN start hot - even with a lot of age.
_________________
82 931

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

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

Here's the check valve I'm speaking of that is used with the "straight through" hose connections:

The other style uses a hose with a banjo-bolt arrangement to make the connection. I believe it's PN is 810.906.093

Click the photos for larger images.
_________________
'79 Eurospec 931

Porscheaddiction · Posted: Fri Jul 18, 2003 3:42 am Post subject:

Can this straight through check valve be added to an '81 with no adverse affects to the fuel sytem.
My parts man at the dealer told me the check valve is on the pump its self and he can get it. But the external valve looks more to my liking( no chance of me damaging the fuel pump in the tank that way.)

Thanks
Chris

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

It is my understanding (never taken one apart) that the "long neck" pumps have the check-valve built into the neck. It is also my understanding that the later cars (81 and newer?) use the "short neck" pump with the banjo-bolt style external valve, and a hose that has a banjo-bolt connection (about $60). The "straight through" check-valve ($16 at dealership) allows folks like me to use the newer short-neck pump, but retain the plumbing that is in the car which was originally outfitted with the long neck pump and internal valve. That make sense?

My original long-neck pump appeared to have the check-valve built in, and had a hollow adapter of the same size with the same thread combinations as on the pictured valve that attached to the line running into the accumulator.

See if this makes the three possible combinations more understandable:

Pump(internal valve)--adapter--straight fuel line--accumulator
Pump(no valve)--straight check valve--straight fuel line--accumulator
Pump(no valve)--banjo check valve--banjo bolt fuel line--accumulator

You should double check the fitting(s) that are on the fuel line running from the pump to accumulator to make sure things will match up, and/or take a look at the prices it will cost to use one style of pump/valve/hose combination as opposed to the other. There may be a mix-match of cars with different hose/pump/valve combinations out there, so we may not be able to say for certain a given year model has a particular setup.
_________________
'79 Eurospec 931

Candayanday · Joined: 11 Jul 2003 Posts: 2

Huge thanks to everyone who has offered help with my problem.

The cold start valve is fairly new and has been replaced, so I now dont think this is my prob. (I hope)...

I have just bought a brand new acumulator.

Fitting this weekend to see if it reseolves issue. Local mechanic thinks it might, as when hot, petrol is clearly vapourising, creating an airlock and then as petrol cant get through, it wont start.

Hope fully this will help retain the pressure.

I'll keep you posted.

Many thanks again, I wish had discovered this noticeboard sooner!

Andy

positivesale · Joined: 12 Nov 2002 Posts: 126

Big thanks for those pics and info about the fuel check valves that are external.

My dealer did mention that there was an external valve for other models of Porsches. I didn't order one because I had no idea if they would work or fit.. but you've checked it out!
I will have to check into PET to see if the late models did use that external type - maybe 944s or something. I don't think there'd be any harm in running two valves because I've run with two pumps with a valve in each. But I guess the flow might get cut down eventually so it's always good to check the flow by doing that 30 second relay test.
_________________
82 931

miguelefe · Posted: Fri Jul 18, 2003 11:09 am Post subject: HOT START PROBLEM SOLVED

After 3 years of hot start problems, I had it solved by a BOSCH Service Center today.
They put a valve in the fuel return line, close to the fuel distributor, conected in a way that it is fully opened when engine runs, allowing fuel excess return to tank, and it is fully closed if you stop the engine.
By this way, fuel pressure does NOT fall after running, and vapor locks are not formed any more!!!!!!!!!!!
I could see that fuel pressure is stable after engine is stopped, the opposite that happened before installing the valve.

NINEEAGLES · Joined: 25 Apr 2003 Posts: 219 Location: SW PA

-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

The fuel distributor has a valve built-in for that purpose. Sounds like miguelefe's fix is a cost effective way of avoiding replacing the fuel dizzy because of a leaky FD check-valve.

The CIS gauges will tell you where the leak is coming from (or if the WUR is the culprit if the residual pressure holds). There are too many possible components that can cause this condition to just blindly start replacing them- fuel pump check valve (internal or external), accumulator(s), fuel dizzy check valve, warm-up regulator, injectors, fuel lines, they can all cause hot-start trouble.

-nick