art

I have blown out the diaphragm twice on my fuel distributor(same cylinder). Everything in the system seems to be right and I am at a loss as to why this would happen.

One thought was that the check valve in the fuel pump was bad which allowed a surge of pressure to hit the FD. I checked it and the pressure bleeds down overnight to a few PSI. This was just with a gauge on the pump output, not the specific CIS gauge.

Could this be the problem? I also had a hot start issue during the short period before this happened.

I definitely have other problems related to idle fluctaution and the hot start issue mentioned above, but I don't think they are part of this issue.

Thanks for any help

Peter Zimmermann

Art: I thought that I had seen every CIS problem - ha! Let us have a little more info; year car?, year engine?, model (2.7, SC, Turbo)?, engine swap car (SC engine in '69T, etc.)?, totally original car? Also, who did you purchase the rebuilt exchange distributor from after the first diaphragm blew?
Pete

art

The car is a '75 Carerra with a '78 3.0 engine. Pump is the correct unit (new) for the SC engine with the internal check valve. Control pressure reg is the 045 correct for the SC. Injectors are new, filter and accumulator are new. FD was rebuilt through SpecialT automotive in Texas. They have a website www.specialtauto.com with all of their info. They send out the FDs for rebuilding, but don't say to who(somebody in Alabama I think).

First rebuild was to correct for 10+ years of sitting, gunk, etc. Second was to fix blown diaphragm (their diag) and third will be for the same problem.

I plan to buy the CIS gauges to check pressures per the correct procedure, but I really can't figure out what is going wrong. I don't want to do this again until I understand it.

What is the third line from the bottom of the accumulator for? It does not seem to show up in most of the system diagrams I have looked at.

Thanks for your interest.

Peter Zimmermann

Art: Because I've never seen, or heard of, your problem, I'd say that the issue is the way the fuel distributor is being "rebuilt." Many years ago, and I'm taking this info from a somewhat fuzzy memory, not notes, I was told that fuel distributors were "not rebuildable" because of the assembly process that Bosch uses. Apparently the adhesive is very special, as well as the press that they use to assemble the units. The press develops about 30K pounds of pressure (this is where my memory is fuzzy!), and that pressure has to be maintained for a certain period of time. I have only used Bosch rebuilds throughout my career, and have never had one leak. It sounds like you've got all the correct components in place, so I think that you might want to try a Bosch unit. Good luck with it!
Pete

art

The rebuilder claims that they have done '00s or'000s of these and have never if ever seen this problem either.

That always seems to be the answer when you have a problem: 'we've never seen that before'. In other words 'you screwed something up and we ain't gonna help you'!

I'm not discounting that, I just would like to know what it is.

RoninLB

I was on phone with a Bosch tech a while ago and he said to never open a Bosch fuel pump or fuel distributor because there is no garantee that it will not leak in the future. That Bosch has a technique for closing them up.

Hladun1

FD's don't break. This points at the rebuilder. If they're not too helpful that just adds to the suspicion. Tell them you post on the Porsche sites and see if that brings them to life. My advice, buy the Bosch part and forget these guys.

CIS systems are very reliable (How’s your EFI system going to work when it’s 30 years old?), but they suffer from being “fixed”. They’re highly adjustable with discrete systems and are generally all screwed up using the “1/4 turn” repair methods.