Leaking CIS?

[Jay Laifman]

I'm pretty sure I know the right answer here. But I thought I'd see if anyone had anything better.

It's been a busy year. As a result, my 73.5 CIS 911T sat for the last 3 months. Over the weekend, I started it up, and backed it out of the garage - letting it idle while I closed up the garage. When I got to the car, it smelled of gas, I opened the rear deck and found fuel coming out in the vicinity of the fuel distributor. It was not coming from the hoses on the top (from the fuel pump and to the injectors). It was not coming from the two hoses in the back. It was not spraying under high pressure. But more than a small drip.

I shut down the car immediately. I cleaned it all off. An hour or so later, I pulled it back into the garage, with fire extinguisher handy. No more leak. I let it idle for about the same time and nothing.

This is too strange. Do I pull out the fuel distributor and ship it to someone to check it over? Or is there any possibility that something happened that caused this to happen but then stop? Something that stuck from sitting? I find it hard to believe. But, I thought I'd ask. Without a decent explanation, there is too much risk to not pull it out.

[larwik]

Hi Jay....if you live in a hot and dry location and the car with CIS sit unused and "dry" for a certain time (say a few weeks or so) it's not uncommon it leaks fuel at start-up....turn off the engine and wait a few hours or to next day...the seals/hoses have swelled-up and it stops leaking...I have two CIS-engines and they act the same way....if you once-in-a-while turn on the ignition (fuel pump) for 10-15 seconds w/o starting the engine the system will pressurize and prime the system and keep it "wet"....I believe it only works with CIS(Higher pressure and flow-rate than MFI)...as to "messing" with the fuel distributor, I hear it's pretty difficult to get them back together and not leak...this is of-course only handling the symptoms...I'm sure someone knows how to properly fix it permanently.../ Lars...

[Jay Laifman]

Thanks Lars. I'm in LA too - and the car definitely sat during the dry 110* days this summer.

FYI, I just found this rebuild kit for the CIS fuel distributor. They sell a set of alignment tools for reassembly too: https://www.ebay.com/itm/Porsche-911.../183460649169?

I know they used to say that Bosch would not supply the right sized o-rings. Hopefully these guys have actually made the right size. I ordered it.

[Jsottile]

Hi Jay – Can you provide a pic of where you think the leak is coming from? I would find it unusual for a leak to develop between the FD halves and consequently a rebuild may not be the answer. There is a nylon supply line at 5 bar, a CSV supply at 5 bar, and a return line. Are you sure none of these were leaking. Everything else is copper crush washers including press relief valve.

Have any fuel delivery components been replaced? If not, this may be an opportunity to go down that slippery slope and replace some 45 year old parts to prevent….well you know.

On the fuel distributor, you can certainly do it yourself. The kit you ordered will work. However, sending it out is probably the smart call. It is a bit tricky. The cast head has shims which are specific to each of the six chambers as well as the valve springs and hats. There are no adjustments. Mix these up, and the party’s over. There is a tiny decoupling bore in the diaphragm that has to line up. Even if you get everything right, then you have to make some secret sauce to seal up metal on metal on metal to get the halves sealed. The only way you know its right is to put it back in and look for leaks and check flow to each injector.

Send some pics if you can. Maybe let the 73.5 sit out in the sun for a week and then energize the pump only and see if you can reproduce the leak and find the root cause.

If you decide to do the head, send me a PM, I might be able to save you some frustration… just a little.

Good Luck

[Jay Laifman]

Thanks. Yes, I am 100% certain that it was not leaking from the supply line or injector lines. I am 95% certain it was not leaking from the two lines out the back of it, from feeling them while the fuel was flowing. I couldn't tell 100% that it was coming from the split. I don't know where else it could be though.

The car is very well maintained, and I have updated or replaced all the other CIS parts over the years. The latest being a WUR about 5 years ago. I've had the car for 30 years now, and whenever there is something not 100% right, I've attended to it.

The seller of the rebuild kit also sells a slick tool to help put it back together correctly: https://www.ebay.com/itm/Bosch-Fuel-.../183420037003?

I got that too.

But first I'm going to start it again and see if it was as Lars suggested. However, that still makes me a bit nervous about when it might happen again.