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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.



Old 09-28-2017, 07:36 PM
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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.
Old 09-29-2017, 12:01 AM
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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.

Last edited by DBabbitt; 10-01-2017 at 08:08 PM..
Old 10-01-2017, 08:02 PM
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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?
Old 10-03-2017, 08:33 PM
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Quote:
Originally Posted by DBabbitt View Post
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.
Old 10-03-2017, 11:54 PM
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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.

Old 10-06-2017, 06:23 PM
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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.


Old 10-07-2017, 07:34 PM
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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.


Old 10-07-2017, 07:57 PM
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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?
Old 10-08-2017, 07:40 PM
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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.

Old 10-10-2017, 09:16 PM
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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.


Old 10-14-2017, 07:02 PM
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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.

Old 10-15-2017, 08:30 PM
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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.





Old 10-15-2017, 08:52 PM
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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.
Old 10-16-2017, 06:52 PM
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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.




Last edited by DBabbitt; 10-26-2017 at 07:05 PM..
Old 10-21-2017, 09:25 PM
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