864kQ2000S4

I've have an old 86 Audi 4000 CS Quattro and have a problem with fuel leaking out of the bottom of the airbox. As background, I did a rebuild of the fuel distributor with a kit that took the car from a massive fuel leak situation and not running (maybe a stuck plunger??) to now where it will start and run fine but with a small fuel leak from the airbox. I suspect return fuel is not going to the gas tank but coming out the bottom of the fuel distributor, through the air filter, and then out to the ground. It will leak while running and for a little while after shut down. I do not see any leaks coming from any of the lines into our out of the distributor or pressure regulator so it seems to be some problem within the distributor itself (but the car starts, drives and idles ok) or perhaps a clogged return line, causing the return fuel to exit wherever it can.

I'm definitely not a mechanic but through google and an eBay kit I got the car running with what appears to be a functioning fuel distributor, except for the leak. I hate to waste gas, let alone risk fire, if I were to drive it. Registration is due soon, so this may be the end of my ownership with this car I've kept running since '86!

Any thoughts of how I can figure out the root cause of the leak Perhaps disconnect the return line from the pressure regulator and see if fuel will exit into a container? I'm tempted to change the differential pressure regulator, but would rather save the money if it could be an easier fix. I'm fairly confident I did a proper rebuild of the distributor since the car runs quite well.

Thanks for any ideas

Rogviler

When you say "rebuilt," does that mean completely opening the fuel distributor? If so, did you make sure to keep track of all the little pieces? And did you use a shellac sealer on the large metal gasket or another sealer or none? Those would be the two main sources of problems with a full rebuild.

Can you confirm that it's coming from the plunger tube versus a seam or line?

-Rog

864kQ2000S4

I did a full rebuild with a kit from CIS Jetronic (cis-jetronic on eBay). It came with all new O rings and a custom made gasket to reseal the two halves together. I even used the special tools they sell to ensure proper alignment of the two halves when putting everything back together. There is no leaking from the seam or any visible connections so I can only presume the leak is coming out the bottom and hidden section of the fuel distributor. I don't know of a way to visually check this while the engine is running other than seeing fuel seeping out the bottom of the airbox at the lowest point and running along one of the big hoses/tubes in that area.

Prior to reinstalling the distributor I checked the plunger and it moved freely and appeared to seat well in the unit. As mentioned the confusing thing is that the car runs nicely leading me to believe the problem is occurring after proper fuel supply to the injectors and cylinders. I just don't know enough about the system to figure out what is happening in this case.

Rogviler

If you take just the top part of the fuel distributor off (three screws) you'll be able to see the bottom of the plunger. Then have someone run the fuel pump (take the relay out, jump the two opposing sockets that are perpendicular to each other) and see if that's where the fuel is coming out. I would bet that it is.

-Rog

Rogviler

Also, see if you can tell whether the fuel is leaking between the plunger and the barrel or the barrel and the housing. That'll be tough, but if it's the plunger then that's easy, it or the inside of the barrel probably has some damage (crappy). If it's between the barrel and housing then it'll be harder to tell whether it's an o-ring or the metal gasket, but that's fixable.

-Rog

864kQ2000S4

As you suggested I lifted the fuel distributor while activating the fuel pump. Good news in that the bottom of the distributor remained completely dry throughout several minutes of activation. The outside of the distributor, including all lines in and out of the unit also remained dry.

The bad news is that the leaking fuel reappeared at the bottom of the airbox and one one of the hoses coming out of it. I've attached a picture to try to explain where this fuel is appearing.

Since the fuel doesn't appear to be dripping into the box from the distributor at the top it must be flowing from the manifold to the hose and perhaps getting enough volume to make it all the way to the airbox. It seems like the only source of fuel would be the cold start valve. When I have the wire hooked up, if I put my ear to it I can hear it making noise. I'm not confident that if I disconnect power to it, it will go to a closed state. I'll run some further tests and let you know what I find. Is there a way to force that valve closed for a test to see if I can get the fuel to stop?

I'm going to reattach the fuel distributor since that doesn't seem to be a source of the problem. Thanks for your help!

2 pictures
1. dry plunger
2. wet hose (orange color) and fuel seeping from the black piece which I think is the bottom of the airbox

Rogviler

Interesting... And just to be clear, it IS fuel, right? They do tend to leak oil through the intake system is the only reason I ask. (I assume you would know the difference, but one can never be presumptuous on the internet.)

Well, given all that I would pop the cold start valve out and do the same test. Ideally it should be closed all the time unless it's powered. It's entirely possible for it to become stuck open or for it to become shorted. Upstream I believe it's controlled by a sensor that could be stuck on. But see if that's what's leaking first.

-Rog

864kQ2000S4

Yea, it is definitely fuel. I just got back in from doing the test you suggested and the cold start valve was also dry. Would the fuel injectors be spraying fuel the whole time, even with the plunger down as you can see? That's the only other idea I can think of because the distributor and all connections are dry. This doesn't necessarily explain why this same leak appears after the car has been running. In that case it seems like the fuel would be burning and not leaking.

Now I have to recharge the battery to continue testing. I'm about ready to give up and call the salvage yard :-)

864kQ2000S4

Ok...after putting everything back together and jump starting the car it started...but you can see how serious the leak is...I did drive the car to the mailbox about a quarter mile away, but after sitting at idle for about 60 seconds I had to be gentle with the throttle at first to get going because I think it was about to flood. After I got going again it drove fine back home. Obviously I can't use it as is so back to searching for ideas.

The video shows the standard noisy valve lifter noise but at a relatively smooth idle with a lot of gas dripping out. The rate seems higher than before the disassembly and reassembly so maybe I aggravated the problem?

Rogviler

Sweet Maria that's a lot of gas. This one's quite a puzzle. I don't think there's any way the injectors could be the cause, since they'd have to not only fill the intake manifold all the way to the top for gas to get into the air boot and beyond, but engine vacuum would make that nigh impossible.

I wish I could see it in person, but I do have quite a bit of CIS stuff piled up, so hopefully tomorrow I can dig into it and see if something stands out.

-Rog