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Discussion Starter #1
Through my related thread on "CIS and Fuel Pressure Distributor Seat" for my 1978 VW Rabbit where I discovered (with the help of others) the control pressure regulator was plugged at its inlet and should be replaced, I found out there were about 60 variations of it by Bosch. Mine ends in a part number of 011, vary basic.

There is a variant that is sensitive to intake manifold pressure during acceleration, thus lowering controlled fuel pressure at the fuel distributor. The plunger raises up to allow enrichment at the barrel slits to the injectors. Within this regulator is an additional diaphragm that drives the rod within the steel pressure chamber. Makes sense to me. Used only during the short time of acceleration.

I trust Butcher and cuppie see this thread with their shop experiences at dealerships. My questions are what part numbers would they recommend if any for my car, how/where would it be mounted in the engine, what cars/engines had this control pressure regulator, were they effective, etc. Appreciate comments from others, too. Thanks.

Are there related threads already started in this regard here at vwvortex?
 

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CIS is vary basic and usually gets difficult because people do not understand it and start mixing/matching parts. Understanding how the system works and having a good fuel pressure gauge can always point you to the right part.

That said, if you have the warm up regulator grafts, you can mix and match to your desire. The regulators all can be adjusted [none were approved by the manufactures]. The question you have to ask yourself, if they are set at the factory perfect, they should never go out of adjustment unless there is something wrong. I have adjusted many to get the car to have a better warm up. Many regulators that were installed on USA engines had emissions requirements that caused a part number change. Checking the graphs usually showed more fuel that would be delivered on Euro variants.

I think the only thing that is critical is swapping fuel distributors with air flow housings. The taper on the housing has a direct correlation with the fuel distributor. I do not think it's a good idea swapping housings. Google I'm certain will prove me wrong.

Unless you are putting in a turbo or making major engine changes, I see little to improve on a properly operating CIS system that was factory designed for your engine.
 

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Discussion Starter #3
Butcher, I ask the question (about vacuum sense input) because with this new used control pressure regulator we have problems getting it to run cold, my wife saying she has to keep reving up the engine to keep it running. OK when warm. I measured control pressures last night, 33 degF ambient, every minute. At start 17 psig, 28 psig at 1 minute, 39 at 2 minutes 46 at 3 minutes, 50 at 4, and 52 psig at 5 minutes. When blanked off, 72 psig. That matches the original readings taking 20 years back. There are no emission controls nor electronics on this car, it would continue running after an electromagnetic pulse bomb were set off.
 

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Discussion Starter #4
Buther, I agree, don't change the air flow housing with the paddle in the middle of the flow. I was mentioning changing the control pressure regulator with one having a different upper cast housing with the boss for a sense line to go up to the intake manifold. It is the device part number 0438140011. They start from 0438140001 and run perhaps as high as 0438140099. Variants, didn't know which one had the boss on it feeding an internal diaphragm, linked to the bi-metal strip.
 

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Discussion Starter #5
0.9-1.3 bar for 10 degC
1.3-1.7 bar for 20 deg C
1.7-2.1 bar for 30 deg C
3.4-3.8 No vacuum, up to pressure.

Readings from a chart on the part number I have. I think my cold readings taken last night match these values.
 

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What happens if you adjust the warm up regulator .5 bar lower?

My statement about mixing and matching was generic. I had a running running 88 Cabriolet [RIP] that had a Volvo turbo fuel distributor/housing and a Audi turbo warm up regulator that ran perfectly. So I know with the right pressures things can run right. I also worked on a lot of gray market Mercedes/BMW that were all cobbled up [add on Lambda systems, poorly adjusted warm up regulators, etc]. Most ran fairly good once the pressures were right. What was right? It was a lot of trial and error with adjusting the warm up regulator pressures. Some were never perfect.
 

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Discussion Starter #7
Butcher: I think I need to go back to the basics and check the auxiliary air regulator, ensure it is open enough when cold.

Back to my other thread on CIS and losing fuel pressure, I found a 3rd passage that is in there per design to bleed down fuel. It is via the small land or groove on the bright metal piston that becomes a capillary for unregulated fuel below the distributor diaphragm to go directly to drain. The drain line also sweeps up from the banjo fitting before turning down so that it behaves like a P-trap, locking out vapors in the return line to the tank from reaching back into the distributor. I think the land becomes the controlled means by which Bentley says pressure bleeds down over a period of time.
 

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The aux air slide valve only allows more air and does not change anything with the fuel. There should be a small nut on the housing when loosened, will allow some adjustment.

Remember, it will not change fuel mixture.
 

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Discussion Starter #9
Checked aux. air valve, its open, still have to start engine 3 times to get it to run. It starts every time but dies 5 seconds later, starved of fuel. The control pressure regulator is working properly with good, cold lower kind of pressures until it warms up and rises to a decent pressure of 52 psig. The output drain line is oriented high so that any vapors go to it rather than to the top of the fuel distributor overnight when shut down. So still thinking this through.
 

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What happens if you lower the warm up pressure .2 bars?

Sorry, we never used any standard values in the shops I worked at for >30+ years. The gauges and specs were all metric.
 

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Discussion Starter #11
Found the Issue

Our same Rabbit has been stumbling while driving for quite a while. I did have the electrical distributor apart a year back and thought it was reassembled properly. But I found there was axial slop in the shaft of 0.050" and with the slanted tooth gear at the bottom of the drive, it would change the timing as it floated. I shimmed the distributor shaft below the flyweights and now the car runs evenly. Doesn't backfire going down hills as much nor stumble while driving. I almost thought I had a bad fuel injector in the CIS system (of the 19 injectors I own) but they're fine.
 

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Discussion Starter #13 (Edited)
The Rabbit still stumbled when running, but I believe I fixed it in the last few days by getting a good, matched set of fuel injectors, tested my way.

For years I would measure crack and seal pressures and if they dribbled any fuel below the seal pressure, never quantified in any way. I used Naptha (briquet starting fluid) and a hand made piston/cylinder assembly from the rear hatchback strut with pressure gauge and appropriate, repurposed fuel injector hose. Can send photos. Also, Dr. Injector, a local injector shop, would rate the 18 injectors I had accumulated for the 4 cylinder engine. They would measure crack, seal, and flow at 70 psig.

I expanded the above my own way. I've measured flow, for 10 seconds, into a glass test tube with ruler inside at pressures of 50, 55, 60, 65, 70, and 75 psig. I plot the pressures on a horizontal axis and the inches of accumulated test fluid (now kerosene) in the 6" tall test tube on the vertical axis. Wow, I found there was guite a disparity. I also measured how many drips came from each injector at 40 psig, theoretically closed, for 10 seconds.

I made 3 groups from the 18 injectors. The first did not open at all until 65 psig, measured maybe 1" in the test tube. At 70 psig, it was a tremendous flow that gushed out of the test tube. The second group started releasing fuel at 55 psig, a bit more at 60, then more at 65 and maybe even lots of fuel. The last group are rejects but worth noting. They either weren't gushing at 70 psig, or they released fuel way too early. When quantifying drips, it wasn't very much. Maybe one drop per 10 seconds, max. Squirt gunning was no longer an issue with me to qualify/disqualify an injector.

I put the first group into the engine and it runs great. Had to back off the allen head screw on the fuel distributor to lean it out. Control pressure starts at 40 psig and slowly ramps up to 70 after 5 minutes. That was always known.

Stumbling was worse with mismatched injectors as I let up on the throttle. Now it is much less with truly, matched injectors.
 

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Discussion Starter #14
In a parallel thread today I mentioned that the Mk 1 CIS 1978 Rabbit 1.5L still stumbles/hesitates/jerks before and after throttle body work. I replaced seals on either ends of both shafts which got intake manifold better at 11" Hg during idle. But this hesitation bothers me. I had also rebuilt the ignition distributor and fuel distributor. Got fuel injectors all matched.
 

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Discussion Starter #15
I got the jerkiness solved. I fixed/replaced the control pressure regulator/warm running compensator. I was seeing 72 psig cold or hot. I replaced it with a used one and was still getting 72 psig. I could measure this running the car. How? By installing a fuel pressure sending unit at the CPR/WRC and an electronic pressure gauge in the car, $110, sold by Max Tow Double Vision.

Opening up the CPR/WRC (original and replacement) the inlet screen area was dirty. Cleaned with carb cleaner and wiped its diaphragm clean of any corrosion from the steel above. Now I see 24 psig cold, 53 psig warm. Now the diaphragm can react to pressures above the fuel distributor plunger on call for more fuel. Diaphragm can release that pressure through the return line to the tank.

I had to read the Bentley manual so many times to figure this out, draw out schematics, do my own testing, etc.

Also had problems with the fuel pump relay not coming on with the engine turning over. Remember the relay has 5 pins to it that used to plug into socket L of the fuse block until VW came up with a recall? That moved only one of its pins away from the block, namely the load side of the 16 amp relay to the pump. I had to move the source side to the relay plus the switched ignition signal away as well so that only 2 of the 5 pins now go through the L socket. Can provide details on request.
 

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That is the bad thing about CIS. All the components must be working properly and the only way to know that is with a pressure gauge. The cheaper the gauge the less accurate the readings will be. As you probably found out, the regulator is pretty simple to disassemble and as long as the parts are not broken, they can be cleaned/reassembled. An ultrasonic cleaner works wonders for this.

Glad to see that progress was made and it's running good.
 
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