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I have a 1978 928 with a VIN in 800's that is pretty unique. Has some unique parts/features to it and is unicorn-like but have an issue. I drive it and get to store or whatever and shut off for 30min or less and it starts right back up on first crank. If I let it site for over 1 hour or more up to 3 hours when I get done with a dinner or something and it takes 5 cranks to start up and catch. Embarrassing in public lol. Sits overnight and start next day on its first crank start-up and no issues. I was thinking fuel accumulator and filter replacement? Attached is my accumulator picture. I was looking at buying one and its like 500.00 for a 78-79 mine, and people say don't use the other ones with only two and screw at top. I was looking at some that were 250.00 and it says 1978 compatible but they don't have the third threaded top hole. What is the difference and which one do I need as I heard get exact part! Any idea on issue as I don't want to replace the fuel distributor unless I have to . This issue has been a pain since I bought it and already did the fuel injectors
There's nothing connected to the 3rd port on your accumulator in that pic- did you disconnect the fitting that leads back to the overflow tank?
Hard hot starting is either bad fuel accumulator or bad check valve in/on the fuel pump. I assume you have the two fuel pump configuration?
Interesting that the issue comes up only after 30 minutes or more, wherever your leakdown is occurring is very slow. (The spec for leak down is that you should still have >23 psi at 30 minutes). A set of CIS fuel gauges would help in your diagnosis.
Porsche used a 3-port fuel accumulator in the first third of 1978 production, then switched to a two port accumulator for the rest of '78 and '79 and changed the fuel line orientation accordingly. I think for a while Porsche used the earlier three port accumulator and just stuck a cap on the third port. That may be what I'm seeing on the accumulator in your picture.
In any case, if your car had no hose attached to the top of the accumulator, then the two-port units that either Mark or Roger sell will work. You might start by checking the check valve on the fuel pump, that's an 80% cheaper solution if that's in fact the issue.
Thanks so much. I will do that this weekend. Doesn’t seem like a hard fix. I really want to avoid the fuel distributor issue. Also, the car would crank and crank and not start the other night but that could be humidity issue with something or maybe passive alarm I just learned about
The reason it starts fine when cold is because erhey cold start injector is supplying fuel. It starts within 30 minutes because the pressure hasn't leaked down enough yet.
If your accumulator was bad, there would be fuel running out of that third port. This is a vent located on the backside of the diaphragm, which allows air to move in and out, as the diaphragm moves. Any hole in the diaphragm would allow raw fuel to escape through that hole.
Before you start replacing parts I recommend you figure out where the leak is (Greg has a nice troubleshooting write up in one of the threads). Often the accumulator, sometimes the built-in check valve in the fuel pump, and sometimes the pressure regulator in the FD. Gauges are a must for troubleshooting. The third port is not essential and I replaced my early 78 accumulator with a 2 port, but as Greg said, if it’s bad yours would leak out the third port.
Before you start replacing parts I recommend you figure out where the leak is (Greg has a nice troubleshooting write up in one of the threads). Often the accumulator, sometimes the built-in check valve in the fuel pump, and sometimes the pressure regulator in the FD. Gauges are a must for troubleshooting. The third port is not essential and I replaced my early 78 accumulator with a 2 port, but as Greg said, if it’s bad yours would leak out the third port.
Perhaps of interest to some:
The two port accumulators have what appears to be a screw in the bottom (or top depending on model year.)
This is actually a vent (the internal diaphragm needs to be able to move air back and forth to correctly function) and also will allow raw fuel to leak out.
The Germans changed to the 3 port design and hooked up the 3rd port to the return line.
This ensured that there would never be raw fuel dripping on the diaphragm failed (inevitable.)
(I have always assumed that this was a "government mandated" change.)
If you see a 3 port accumulator with the 3rd port open to the atmosphere, you can be absolutely certain that the accumulator has already been changed once....the factory never did this.
When building my Spyder it had a 3-port accumulator and it was difficult and expensive to find a replacement but I did. Maybe they're more available or cheaper now, or maybe not, but I'd use the right part for the way the plumbing on the car is setup.
07-21-2023, 01:16 PM
1978 928 starting/fuel issue - help please
