Hi there, I'm new to rennlist. I am piecing together a Porsche 928, 1980 4.5l Euro model.

The issue that I have is that when testing the fuel distributor, when "idling" (no airflow, lever arm isn't pushed down at all), the fuel distributor only sprays out of 1 injector with a high pressure (so high it doesn't mist, and you can see the spray pattern clearly), but as soon as you push down on the lever arm then the rest of the injectors spray.

Is this the normal operation of the fuel distributor, and if not, any ideas on where to look to try rectify this issue?

Thanks

 

This is a great resource for CIS related issues

http://www.928classics.com/4/post/20...ide-78-79.html

 

They should all spray the same.

With the arm up, none should spray.

 

Try swapping injectors to see if it's the injector or fuel distributor.

 

medipedicman: thanks for that, i'll definitely check that out.

LT Texan: they do all spray but only once i start to push down on the arm. As soon as the arm goes up to its resting position (all the way up), only one injector is open, the one right on top of the fuel line to the starter valve.

Jadz928: I have swopped out the injectors, and the same issue occurs. Sometimes though when I swop it out, the high pressure just moves to another injector, normally the one just over the inlet line, but sometimes its random.

 

Just an update: I tested the injectors, they're all fine and unblocked. I believe the problem lies in the fuel distributor, because I disconnected all the fuel lines that connect the injectors to the fuel distributor, and I sprayed carb cleaner into those holes while the arm up. There was no flow for 5 of the 8 holes, but for 3 of the holes there was a flow that leaked into each other and into the start valve outlet.

Any ideas what could cause that? My guess is that the small o-rings on the inside for the 3 that are leaking into each other aren't sealing.

 

Well you've confused me.

There are 8 injectors to the intake runners and one "cold start" injector to the plenum on your model. (If I remember correctly.)

How can the 8 spray when you push down the arm with 3 clogged fuel lines to them?

And are you saying that the cold start injector is always open?

 

LT Texan: okay let me clear up the confusion. Yes that is correct, 8 runners and 1 "cold start" injector.

There is no blockage in any fuel lines. Its when the arm is in the "idle"/arm completely up that 1 of the runners is still spraying whilst the rest do not.

the cold start injector is always closed.

 

If with the arm up an injector sprays, either the fuel injector is bad or the fuel distributor is bad for that cylinder.

As suggested, switch fuel injectors to isolate the problem.

 

LT Texan: swopped out injectors, same problem occurs. So the problem is in the fuel distributor. Where would the problem lie inside the fuel distributor though?

 

Since the problem did not follow the injector, You'll need to replace the fuel distributor with a new or rebuilt unit. Or rebuild it yourself. There is a link to a rebuild procedure on the link in the second post.

 

What's happening is your fuel distributor diaphragm (thin metal plate btw the two halves) is no longer sealing on at least one port.

Also worth noting, the link mentioned above offers a rebuild service too... for those not inclined to diy their FD.

Here's a shortcut to it - http://928classics.com/cis-service-and-parts.html

 

Good point Jim.

Rebuilding yourself is not for the faint of heart.

High pressure gasoline and leaks.

It does seem like sealing it up is a coin flip from some of the stories.

 

I've just ordered the parts for a rebuild, hopefully that sorts out the issue. I will keep you posted on how that turns out.

 

would one recommend sealing the inside with liquid gasket maker or grease?