924Board.org

[Doodle]

When I first bought my car, 6 years ago it had a hot start problem. Let me down the second time I drove it. At that point, I did an in depth assessment of what I had bought and decided anything less than a full restoration probably wasn't worth while. Six years later it's fully restored. Virtually every moving piece having been replaced. I've still got the hot start problem.

My most recent and disturbing discovery in the quest to solve the hot start problem involves the fuel distributor. It's not the right one for the car. As with the Haynes manual I'll talk in terms of Bosch Part numbers.

According to Haynes, Page 78, section 6-6 the original fuel distributor for my car is the 039. The only replacement available for the 039 is the 005. By the way, according to my sources the 005 is now out of production. A P.O. had kindly upgraded my fuel distributor to a 007. The 007 was designed for 1.6L Volkswagen & Audi, 08/75 thru 07/80. The Haynes then goes on to explain that when replacing the fuel distributor with the superceeded part, the fuel accumulator must also be replaced as the 039 accumulators are not compatible with the 005 distributor.

I wish I had questioned the above information sooner, as too this point I have replaced every component in the fuel supply chain from the tank too the injectors and back again in the hope of eliminating the hot start problem. The fuel pressure leakdown tests still indicate a rapid loss of system pressure after shutdown. There are no leaks.

Based on the above information I believe I might have the wrong fuel accumulator setup for the existing fuel distributor. I have the two 20cc fuel accumulators commonly found on the early cars. Can any one tell me what the correct setup might be, or care to comment?
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Doodle
Pre 77.5 Mars Red

[Smoothie]

[thane]

i used to have a hot start problem and 1-2% of the time i still do, but usually starts on 3rd or 4th go. Originally, i used to have to leave it a minimum of 30 mins before she would even think about firing up agian. I then got a new fuel? relay put in and things have been smooth sailing ever since. Dont know if this helps u or is even relevant but just in case.....sorry if im way off
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1982 Porsche 924 125hp

[Doodle]

Sorry Smoothie, by rapid pressure loss I meant over approximately the first half hour after shutdown when performing the leak down tests. After 1/2 hour pressure has dropped to nearly zero. No leaks and the two accumulators are new. Of course new doesn't necessarily mean good but no leaks when I pull the bottom screws.

I believe I need to investigate further the statement in the Haynes regarding the relationship between fuel distributor and accumulators when updating one or the other. The Haynes states pretty emphatically that the new distributor won't work with the old style accumulators. I'll check with the Dealership when they re-open tomorrow. Perhaps they can shed some light.

Thanks for the suggestion thane, but I've already replaced the VW fuel pump relay which came with the car, with the correct one from Porsche and the new one tested OK a month ago.

I did encounter some other parts wierdness when I replaced the fuel pump. The correct pump for my car is the long neck one with the check valve supposedly built in. In order to fit the fuel line from the pump too accumulators I had to buy the spring loaded type check valve to accomodate the banjo type fitting on the fuel pump end of the line. I understand the spring loaded check valve is for the short neck style pump. I now assume I actually have two check valves at the fuel pump? This issue also leads me to suspect perhaps the wrong accumulators for the fuel pump and fuel distributor.
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Doodle
Pre 77.5 Mars Red

[Smoothie]

I don't know what they could find incompatible between the fuel accumulators and fuel dist. A fuel accumulator is just a spring-loaded rubber bladder. Different fitting sizes on the accums can be incompatible with the fuel lines, but other than that I can't imagine. The car runs ok, right? That would seem to rule out a compatibility problem. -And if the car runs ok, then having 2 pump check valves in place isn't causing a problem and could only help to hold pressure in the system.
Maybe try some temporary insulation between injector lines and engine/head to rule in or out whether it's a vapor lock problem.
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"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[-nick]

I agree with Smoothie- I don't know what the Haynes is talking about when they say to change the accumlators to match the fuel dizzy. 2 20cc accumulators hold exactly the same pressure as one 40cc accumulator. The only problem I could foresee with using a VW fuel dizzy is that it may have a different "map" of fuel delivery. ie, the dizzy may give less fuel when the air metering plate is at X height or less fuel at Y height than the 924 dizzy.

Anyway, with the CIS gauge you should be able to somewhat isolate where the pressure leak is coming from. Old hoses are always suspect.

-nick

[Lizard]

I know that you replaced nearly everything in the system, however if or when you replaced the fuel pump did you replace it with a fuel pump with a built in check valve, or did you reuse the old check valve, some of them the check valve resides in the fuel pump itself other screw into the end of the fuel pump and then the banjo fitting attaches onto it,

might be a thought to replace that first, or try to source out an inline check valve that is able to sustain the 75PSI mark that our cars run at.
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3 928s,

[Doodle]

I've just found a major intake manifold leak at the #4 runner. I'll have to fix this before I can start chasing the hot start problem again. Maybe it is somehow related?
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Doodle
Pre 77.5 Mars Red

[Chrenan]

Doodle,

I question whether the accumulator matching the fuel distributor can have such an effect. My car came originally with the larger 40cc accumulator. This spring it developed a leak. I had previously received a new-old-stock small 20cc accumulator in an EBay grab bag of 924 items. So, as a temporary fix, I swapped the leaking 40cc accumulator with the single 20cc version. This temporary fix has been in my car all summer. I have not had a hot start problem this summer at all with this setup. I did experience hot start problems when I first got the car, but replacing a laundry list of items related to the fuel, spark and air systems has solved any hot start problems, and the problems have not re-surfaced with a switch to a 20cc accumulator. I can't imagine why you are having this issue after the extensive work done to the car.

I don't know if these items will help you at all, but I have 2 kits that were used to convert the early 924 with a single 20cc accumulator setup to a double 20cc acccumulator setup (with German instructions). The kits consist of some funky fuel hoses, mounting brackets, and other smaller items that I don't recognize from my 1980 924 rear fuel line assembly. If you'd like one (or both), drop me a PM and they are yours for free. I'm not sure they'd help with anything, but the replacement hose might be handy.

Chrenan
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1987 951 - M193 Version for Japan

[Chrenan]

Technical Bulletin regarding hot start problems for 1976 924 and how the kit I have is a fix:

http://944faq.986.org/KevinGross/TechBulletins/TB76_01/TB76_01.htm



Another Technical Bulletin regarding hot start problems for 1977 924:

http://944faq.986.org/KevinGross/TechBulletins/TB77_05/TB77_05.htm
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1987 951 - M193 Version for Japan

[Doodle]

Wow thanks Chrenan for the links. This is potentially excellent information. These bulletins indicate that even with a leak proof system and all new components it may still be possible to experience hot start problems with the early '76/77 models. Interesting, the solutions put forward by Porsche.

I'm still waiting for a replacement intake manifold gasket to arrive. It should be here the beginning of the week. While waiting for it I decided the logical thing to do is start again. Assume nothing. Just because parts are new doesn't mean they are working properly.

While checking the wiring connections and specs for the individual fuel system components I found a short too ground in one of the wires from the thermo time switch. This may have been preventing the cold start injector from providing that initial 10/12 seconds of extra fuel at cold start. Perhaps in the end my hot start and running problems will end up being a litany of minor things.

I'll keep the group posted.
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Doodle
Pre 77.5 Mars Red

[dpw928]

Doodle,

A leaking cold start valve could cause the pressure leak down as well as your hot start problem. Have you checked or replaced it?

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

[Doodle]

Yeah, I replaced the cold start valve with a new one this past spring. They're VERY pricey. As soon as I receive the new intake manifold gasket I'll start testing the fuel system again. I plan on starting at the beginning. Just because a component is new doesn't mean it's working properly. Thanks for the suggestion Dennis.
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Doodle
Pre 77.5 Mars Red

[ponchojuan]

I'm assuming you have follwed the Haynes Manual concerning the pressure testing process, including the cold and hot checks. DOing them all, and in the right order, really helps ferrett out the likely cuprit.

Remember that over pressure is bad news on starting as well.

Also, if you finally find you need to repace the fuel distributor, there is a guy in Texas who will rebuild that 005 for $139.. and warranty it for a year. http://www.specialtauto.com/

His name is John Hervey, and he specializes in CIS. His specially is DeLoreans.

He can also make you a snazzy set of SS injector hoses!

[ponchojuan]

Typo. I mean't $359. Still not a bad deal.

You can get a warm up regulator rebuild for $139.