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DBabbitt 09-28-2017 06:36 PM

CIS Injection Loses Pressure
In my 1978 VW Rabbit with CIS, 4 cylinder, from Canada and minimum emission controls, I'm loosing pressure overnight so that it takes 1/2 mile of road driving to clear the "air" from the system. I've changed fuel pump check valve several times and disassembled the fuel distributor's pressure relief to inspect. I've checked fuel injectors that they open/close with pop/seal as well as the 5th injector. I've replaced the fuel system accumulator.

Could I be loosing fuel past the fuel metering plunger in the barrel? Could CIS-Jetronics do something in that area? What if the slots in the barrel are misformed?

By the way, VW said to never open the fuel distributor and I know why, hard to seal. What works is a homemade gasket made of 0.001" aluminum foil that fits agains the metering diaphragm.

Golten951 09-28-2017 11:01 PM

If you have a bad fuel pressure accumulator it can cause that, Had the same issue with my 82 Porsche 924, which shares A LOT with the VW CIS. Changed out the Accumulator and it solved the problem.

DBabbitt 10-01-2017 07:02 PM

That's what I thought too, bad accumulator. Replaced it, no improvement, so now I have a good, used, spare accumulator.

I checked with CIS-Jetronic and they recommended sprinkling baby powder at the fuel distributor's mid-line and below it but above the Air control box to find leaks. Problem is, can't gain access to 2 of the 3 screws as they're directly below fuel lines. I do think I'm losing fuel past the plunger. Don't believe there are O-rings around it.

I have 2 fuel distributors. The first one is the only one I've completely disassembled, sealed with an aluminum foil homemade gasket, put it into use, no leaks at the mid-line but had fuel delivery problems. I think the slits in the barrel are deformed. So I removed/replaced with this distributor and after a year in use, am losing fuel from it overnight. It does fill back up but takes 1/2 mile of driving for that to happen.

One of the two distributors needs to be examined closely for clearance issues with the plunger while the other keeps us driving.

DBabbitt 10-03-2017 07:33 PM

Would you think one path for fuel to return to the tank could be via the control pressure regulator/warm running compensator as shown on the right side of the Bentley fuel control schematic above? Could another path be by the pressure regulator above it, lower half of the fuel distributor body?

Golten951 10-03-2017 10:54 PM


Originally Posted by DBabbitt (Post 9762292)
Would you think one path for fuel to return to the tank could be via the control pressure regulator/warm running compensator as shown on the right side of the Bentley fuel control schematic above? Could another path be by the pressure regulator above it, lower half of the fuel distributor body?

That does have a possibility of causing a leak down. Sadly I do not have a huge amount of knowledge on the CIS system, But if the Pressure regulator is failing can cause your issues. My 944 pressure regulator failed, and would take several seconds before firing off. like the engine would crank like ten times, changed the regulator and problem solved. silly question, but have you verified all the fuel lines in the system? seeing if you have a leak lingering. The crush rings can wear out and not torque correctly. replaced all of them in my 924, least 7 of them were smashed and leaking.

DBabbitt 10-06-2017 05:23 PM

I had considered fuel injectors leaking after a short run, cold engine shutdown. I pulled them out and placed each in its own test tube and checked after time. No fuel leaked.

I don't think I'm losing fuel pressure via the control pressure regulator as it is 2 feet lower in elevation than the fuel distributor. There is no gravitational way for it to leak fuel back up to the area of the distributor, then back down again to the return line to tank.

I think I'm leaking fuel past the bright stainless steel end of the pressure regulator which I show completely disassembled at the top of this thread in the photo. Like a leaky faucet washer in the house, it is leaking past the end of the regulator and its seat with the fuel distributor.

I'm also making a tool to check that the fuel pump check valve is not leaking. It will be like a big nut with air fitting on the high pressure side. I'll pressurize and place under water to check any leak rate. I now own 4 check valves. Two are new. The new one in place now may be the cure. Jury is still out.

DBabbitt 10-07-2017 06:34 PM

I made a tool today to check for leakage past the fuel pump check valves. Apply air into the Schraeder valve, place the check valve end in water and look for bubbles. All the check valves I've used the last 3 weeks check fine, so I'm losing fuel somewhere, perhaps through the fuel distributor, overnight.

DBabbitt 10-07-2017 06:57 PM

Here is where I think I'm losing fuel overnight. I don't see this listed as a possibility when I read a troubleshooting guide.

Golten951 10-08-2017 06:40 PM

Your certainly have explored the roads! I am impressed. I do see what you mean about that valve in ths CIS housing. Possible the spring is worn out?

DBabbitt 10-10-2017 08:16 PM

I made another tool. It will be installed at the fuel return line banjo connection, in lieu of it, after a cold engine shutdown. I'll put a test tube at the Schrader valve (minus its spring seat) to see how much fuel would otherwise be pumped back to the tank through it (should be none, but there must be some) from the fuel accumulator. If the pressure regulator leaks at its seat, this will show it.

DBabbitt 10-14-2017 06:02 PM

I found the leak, whether it is supposed to or not I don't know, but it occurs for an hour at the return line to the tank at the fuel distributor. You can see the gas in the clear fuel test line about 20 minutes into the drain down. The accumulator unloads itself through the distributor via two pressure paths, perhaps directly through it or out to the warm up compensator and back to the tank via the distributor. Takes an hour to do it.

Of course, takes around one to two minutes of running the engine to fill it back up again and charge the accumulator. Again, this is on a VW Rabbit, 1978, CIS. I need to learn about the passages in and around the pressure regulator, how the piston and O-rings work.

DBabbitt 10-15-2017 07:30 PM

In these next two posts I'll show something new that the Bentley manual doesn't address and that is that the pressure relief valve provides two functions: 1) to control pressure during running and 2) to completely isolate it from the fuel tank, to shut it off, during shutdown.

I'll provide 3 sketches in this posting, the next will show photographs of the red colored shut off section of the pressure relief valve on the left side of the drawing.

DBabbitt 10-15-2017 07:52 PM

The photos show the left side of the pressure regulator of the fuel distributor. Note the O-ring on the head of the red "pin" or nail that seals off the warm-up control (WUC) regulator on shut down. Opened when the silver piston of the pressure relief shifts left.

Photos taken 2 years ago when I didn't know its function. I wonder if the rebuild kits for this include 3 O-rings for the pressure relief valve.

If a new O-ring doesn't seal off the WUC, another option could be to trim off the pointed red end on the right side where it hits the piston. Would allow the O-ring on the left end to have more squeeze to it.

DBabbitt 10-16-2017 05:52 PM

CIS-Jetronics has the repair kit, very reasonable, has all the O-rings it appears from the packaging. This is a sub product of American Precision Machine it appears.

DBabbitt 10-21-2017 08:25 PM

I replaced the 3 O-rings associated with the fuel distributor's pressure regulator and WUR poppet valve and am still leaking fuel, at the same rate as before, after shutdown back to the fuel tank. Takes an hour or so. I'm wondering if the seat at the piston end has a crack. The poppet valve O-ring was brittle and had to be whittled to remove/replace it. But it is the right side, by the piston of the pressure regulator, that I think I'm losing fuel after shutdown.

What is acceptable for volume to leak down? I know the pressure is supposed to slowly recede per Bentley, but how much volume of fuel is to leak by and from where? Can't be the midline of the main steel gasket plate. It is in the lower half of the fuel distributor.

One photo shows how to push the piston out after the bulk of the valve is removed. Do it via the supply fuel line to the WUR by feeding in a copper wire.

DBabbitt 12-12-2017 06:55 PM

Thanks to and this web site, I found the problem with my CIS pressures. This AM with it below freezing I took new pressure readings with the test valve open and closed and in all instances read 72 psig. I surmise the warm up regulator (control pressure regulator) is stuck closed so that for the first 1/2 mile of driving, the car always ran lean and "stumbled" under any load.

I've ordered a replacement and between it and the old should have the car running as it should. I was putting too much rocket science into the situation as current pressure readings should have led me to a resolve sooner.

DBabbitt 12-16-2017 06:29 PM
After installing my new used control pressure regulator which works fine (actually, it is still causing us to have to rev the engine when cold, OK when warm) I disassembled the original to find where it had plugged up as it behaved that way. Didn't know it had a screen behind the larger banjo union, the inlet.

Completely disassembled it to include the electronic plug via its C clip and the bimetallic metal. Removed 4 screws holding the pressure assembly together and put the upper shell upside down in warm soapy water in an ultrasonic cleaner until one could blow air through the small inlet orifice. Should work fine as a backup.

DBabbitt 12-30-2017 06:32 PM
I found a 3rd passageway for fuel to drain from the fuel distributor after shutdown. It is via a land or groove around the piston that faces unregulated pressure from below the distributor diaphragm, opposite the drain line banjo. It isn't a large passage, almost capillary in size.

Also note that when installed in the car, the drain line is directed up before going down to return to the tank. Keeps any vapor that might accumulate in the line away from the distributor but trapped in that small arch.

DBabbitt 01-02-2018 07:00 PM

Despite checking the aux. air regulator (its open), replacing control pressure regulator and dressing the drain line of the fuel distributor higher than itself, still is difficult to start. It starts 3 times but runs only 5 seconds each time, starved of fuel. The 4th time it runs and when warmed up, runs fine. Still thinking this through.

DBabbitt 09-01-2019 12:33 PM

I've also rebuilt the throttle body sensor by replacing packings on both ends of both shafts. Intake manifold pressure at idle improved to 11" Hg, but the car still shudders, jerks, hesitates when running. As though there is air in the fuel lines, but that can't happen with a pressurized system. Don't see leaks anywhere. Don't think they're in the fuel distributor, either.

I have dimensions on all sorts of things for the throttle body if interested, such as if screws are stripped and can't be re-installed in the butterflies.

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