Thinking of converting from CIS to carb

82vdub · Post by **82vdub** » Thu Dec 03, 2009 10:04 am

With my new 86 gas Jetta, apparently the control pressure regulator (commonly called the warm up regulator) is bad. It's fuel pressures are just a hair out of spec from what the Bentley manual lists (plus the resistance is definately out of spec). I'm finding replacement parts on fleebay for $300, but I'm afraid that this fuel system could cost me a lot of money to fix, if this doesn't completely fix the issue.

Anyways, I was thinking of converting to a carburetor setup. I believe that the 1980-84 Rabbits had carburetors on them, and some of them with two barrel carbs on them. The intakes from these 1.5-1.8's should fit my 1.8L gas engine, right?

Does anyone have a complete carb/intake/air cleaner setup that they want to sell? For those that have converted or worked on these cars, does anyone see any issues with converting to a carb setup? I realize the fuel pump under the car has to be bypasses, but what about other issues that I may not have thought about? What carburetor (Bosch, Solex, etc) came on these and anyone see any downsides to this? All thoughts are welcome. This is my winter car, and winter is knocking on the front door......

Harry · Post by **Harry** » Thu Dec 03, 2009 10:22 am

Check out redlineweber.com, I think it is. I did this several years ago to my 77 Audi Fox. By-passed fuel pump, accumulator, etc. and added a Facet brand fuel pump and did a little mod of the throttle linksge, as I recall. Had to fiddle with the line from the tank going forward to engine, a bit, as I recall, nothing really hard. Just have the gasoline way down on the tank-fuelline thing when ya do it, don't wanna go ka-boom!!!

Uses Weber progressive 2-bbl, works pretty good. My old Audi has automatic so mileage is only about 27-29mpg, but the auto is nice at times. Getting old I guess.

The old original Zenith 2B2's, or whatever they were, were dogs to get right, I was told.

Vincent Waldon · Post by **Vincent Waldon** » Thu Dec 03, 2009 12:07 pm

Harry wrote: The old original Zenith 2B2's, or whatever they were, were dogs to get right, I was told.

100X... as I recall poor fuel economy, lots of flat spots in the acceleration curve, etc etc etc.

On the other hand it may be all you can find... but if so just don't pay a lot if you can help it!!

Vince

bscutt · Post by **bscutt** » Thu Dec 03, 2009 1:40 pm

My first Rabbit was a '75 "Swallowtail" as they now call them and came with the 1.5 gas motor with the Zenith carb. What a useless piece of crap. I replaced it with the Weber setup and threw in some cheap headers, mileage went from 22 (awful) to 27 mpg and power went up by a good 25%. I used to beat early GTIs in it. Anyway the weber was a great carb and the only problem I had was that parts would vibrate off unless I kept the idle speed up high (kinda like a MK1 diesel).

So if you can locate a weber carb setup (try the vortex) it should work well for you. Converting from the FI setup might be a little challenging but the early cold start setups were not known for their reliability and fixes can get expensive.

Quantum-man · Post by **Quantum-man** » Thu Dec 03, 2009 5:36 pm

My first Passat had a manual choke, twin throated Webber put on it. It went really well. Other's with the auto choke, [pierburg] could be tempermental with al the unneccessary control bits. Converted my last Passat to diesel a few years ago.

bvolks · Post by **bvolks** » Thu Dec 03, 2009 6:22 pm

I just sold a Holley 2 barrel carburetor and intake off an early Omni that came with the Rabbit motor for $20. I don't know if they were any good or not but that might be an option too if you can find one.
I know a guy who was having trouble with the CIS injection on his Cabriolet and he switched it to the Digifant II system from a newer Jetta. He claims it is a very easy swap if you can get ahold of the parts.

wolf_walker · Post by **wolf_walker** » Thu Dec 03, 2009 8:09 pm

I have to say on principle, that a well tuned CIS is a beautiful thing.
My last 85 Scirocco 8v bone stock turned in consistant 38mpg in combined driving and started perfectly in any extreme of weather seen in eastern N.C.
I miss that car.

I have a couple dgv-5a's kicking around, been trying to find a use for them.
I don't think I can fit them both on the Mercedes unless I bulid an intake.

Quantum TD · Post by **Quantum TD** » Fri Dec 04, 2009 2:47 pm

You can clean and recalibrate your Warm up Regulator (WUR, also known as the control pressure regulator). They're easy to take apart, and with a CIS pressure gauge and a means to know the ambient temperature, you can calibrate a used WUR pretty easily:

http://www.pelicanparts.com/techarticle ... up_reg.htm

There is tons of info on the vwvortex about diddling with the WUR. You can also find used ones cheap:

http://forums.vwvortex.com/zerothread?id=4673384

You can get a rebuilt one pretty cheap too. IMC parts carries them for about $50 for a jobber, plus a $25 core. A fair retail price is about $75-125.

Quantum TD · Post by **Quantum TD** » Fri Dec 04, 2009 2:52 pm

Also, the upside to your 1986 is that it has a plastic gas tank. The real problem with CIS is the metal tanks that rust and spew crap through the system. If you fuel tank is clean, and everything else is working, then chances are the only parts that may be bad are:

Injectors: spray patterns get goofy after not running for a while. You can pressure pop and clean them using your diesel injector tester (the threads are the same: Bosch).

WUR: As you've found out. At stone cold, your control pressure should be about 15-25 pending the temps. Once the car is warmed up, it should be about 48-55. If that checks out, then you just need to adjust the fuel distributor to get the prop fuel air ratio.

O2 sensor: they're cheap and easy to replace. They are the heart of the CIS system on those cars

Frequency valve. If your control pressure is zero, or 70-80, then your frequency valve may be stuck closed or open (not sure which). They're easy to replace, and no need to buy new.

82vdub · Post by **82vdub** » Fri Dec 04, 2009 3:03 pm

I appreciate all the comment and really at a crossroads on what to do. I sure didn't intend until December to start to wrench on the winter car, as I felt I could get it running decent way before then, or have decided that I couldn't long ago and work on swaping the engine or something. I'm just not 100% convinced that it's the control pressure regulator that's causing the issue. I also stopped by a foreign car repair shop today that's down the road from work. They have lots of Audi, VW, Volvo and Porsche's outside and in the shop. The parts guy there said that from the symptoms I described, it doesn't sound like a control pressure regulator.

Quantum, the fuel pressures are a couple psi out of spec from the Bentley manual, which the guy today said that's no big deal. But, with the control pressure regulator plugged in or not plugged in, it still runs the same cold and the same warm, no matter if it's plugged in or not. That tells me that it's not necessarily this unit that's bad.

Tank was pulled and drained and cleaned, injectors tested for spray and flow (#3 was flowing little less fuel) and CO2 was adjusted (by my mechanic). It's cold out and I can't work outside like I used to be able to a few years back. I wish there was someone close by that has messed with these gas motors that I could get another opinion and another hands on with. Maybe I should run it by this shop down the road and see what they can diagnose. But, if it's going to cost me $1000 and many parts replaced just to get it running right, a carb setup would probably have been better in the long run.

wolf_walker · Post by **wolf_walker** » Fri Dec 04, 2009 6:30 pm

Quantum TD clearly knows em better than I, but they are truly a simple system once you get the jist of what they were trying to do with it.
I started on mine with the assumption that somebody had screwed with every adjustment, that it was filthy, and all the wear items were worn out.
I tested and adjusted and proved right or wrong all of that and ended up with a wonderful system after going through the book. As I recall I cleaned the WUR on that one, little
screens had a small amount of deposits, cleaned the injectors in an ultrasonic bath, centered the air flow plate and adjusted something else on it.
After the fresh correct O2 sensor and verifying a good ground the rest was tuning timing mixture. That car made a believer out of me, I was pretty concerned with having a CIS vehicle of that age when I bought it.

That being said it was spring and I had time and money to burn, so I understand your point. If you can really find a shop that knows them well it might be better that way. That's a big if in my book, having a lot of euro cars sitting out front don't make a shop good, but it's a start.

As an asside there is a really neat digital WUR one can plug in a laptop and play with I'd love to get my hands on sometime.

bvolks · Post by **bvolks** » Fri Dec 04, 2009 11:56 pm

Quantum TD wrote:Frequency valve. If your control pressure is zero, or 70-80, then your frequency valve may be stuck closed or open (not sure which). They're easy to replace, and no need to buy new.

Where is this located?

wolf_walker · Post by **wolf_walker** » Sat Dec 05, 2009 1:44 am

bvolks wrote:
Quantum TD wrote:Frequency valve. If your control pressure is zero, or 70-80, then your frequency valve may be stuck closed or open (not sure which). They're easy to replace, and no need to buy new.
Where is this located?

Was near the airbox on the scirocco, two pin elec plug, fuel line goes through it heading to the fuel dizzy, it should buzz when it's working seems like. On the older CIS, the lambda was an add on such that one could disconnect it and it became a non auto adjusting CIS again. The idea was it helped keep it a little closer to target AFR, having the freq valve reading off the 02 sensor to vary fuel pressure some. I think that's how it went on VW's anyway. Lot of the Porscche guys ditch it all together.

Quantum TD · Post by **Quantum TD** » Sat Dec 05, 2009 3:27 am

bvolks wrote:
Quantum TD wrote:Frequency valve. If your control pressure is zero, or 70-80, then your frequency valve may be stuck closed or open (not sure which). They're easy to replace, and no need to buy new.
Where is this located?

The frequency valve is located on the side of the fuel distributor. Basically, it's a round solenoid with fuel inlets and outlets (one on each side) and a 2-wire plug on it.

As for 82DUb, I think you're on the right track.
This is how I would approach it:

1) Clean and flush tank: DONE!

2) Check in tank and external fuel pump: CHECK!

3) Check the fuel accumulator (it's located on the side of the fuel pump reservoir). Undo the screw on the tail end of it. If fuel comes out, it's bad. New ones are NOT cheap. But, this probably won't cause your car to run poorly. If anything, it will be hard to start, especially on hot days (vaporlock).

4) New check valve on fuel pump? These are 'relatively' cheap. They screw into the fuel pump delivery end. If they're bad, they let fuel drain back to the tank. Again, it won't make your car run poorly, but you may get vaporlock on hot days, or have to crank a while before it will start on any day

5) Fuel lines cleaned: CHECK!

6) Fuel system pressure tests: You'll have to do at least 2 of them.
a) System pressure: Put on your 2-way fuel pressure gauge and
jumper the terminals. Check your pressure. It should be about
68-74. If not, you can check the pressure relief valve. It's got a
16mm head and screws into the side of the fuel distributor. If you
pull it out, check for ripped seals. There is also a part of the valve
that may stay in the dist when you pull out the spring part. Slip a
magnet in there and pull it out. You'll need to check the rubber seal
on the tip. If that all checks out, you can install shims on the spring
to raise the pressure into specs. New relief valves are available from
Bosch. My wholesale cost is like $30, maybe you can find them online
for about $50. They come with an assortment of shims to adjust
them.

b) Control Pressure. Looks like you've already checked this route.
Here's the best way to test. Install your 2-way pressure gauge. Open
it to the WUR. UNPLUG the electrical connector to the WUR. PUll the
fuel pump relay, and jumper the terminals. When cold, you should
see about 20 PSI. I think that's the lowest they'll go in any condition
(unless you alter them to run richer: i.e. lower control pressure).

Start the car with the gauge hooked up, and the electrical connector
hooked back up to the WUR. Watch the pressure gauge. It should
slowly increase and stabilze at about 48-55 psi (mine stops at 52,
and it was rebuilt recently). If you cannot get those higher numbers
for control pressure, then the unit is faulty. You can test the
resistance on the electrical unit. It's not the most-reliable indicator,
but as long as you have about 18 ohms, it should be good. Again, the
big thing is having the correct pressure. It doesn't matter how you get
there (i.e. engine heat or heated rod). If you can't get the pressure
right, everything else will fail.

c) You can also test for residual pressure, but as noted above, that's
only if you have hot-start problems.

7) Test Frequency Valve: This is outlined in the Bentley. Check the resistance and check for power at the valve. If the resistance is OK, and there's power at the terminals when you jumper the fuel pump, then you're ok. If you have no power at the plug when you jumper the fuel pump relay, then your CIS ECU relay is bad. It's the silver metal relay with the # 26 on the top. These go bad. When they do, your car runs ONLY in CIS basic. In other words, the oxygen sensor is reading the exhaust and trying to adjust the mixture, but there's no communication to the computer. When this happens, your frequency valve will NOT work. When it's working, you will hear it buzzing when the car is running. If not, you've got to figure out if it's the wiring, the relay, or a bad frequency valve. They don't go bad often, but they do.

Dwell meter test. Hook up an electronic (or old analog) dwell meter to the CIS test plug. It should be zip-ted to the cold start injector (one brown wire, one blue wire with a white stripe hooked into a white plastic plug). This will measure the duty cycle of the frequency valve. With the car warmed up and all electronics and fuel pressure good, the frequency valve should be running 50% duty (45 degrees on a dwell meter set to 4 cyl). Adjust the fuel mixture via the fuel distributor 3mm screw until it reads 45 (50%) at idle.

That's it!

Now, you could have a bad fuel enrichment switch (on top of the throttle body), or a bad temp sensor on the water jacket (front of head). But these really won't affect too much. If anything, your car will run a little richer, which would be smoother.

Good luck.

Quantum TD · Post by **Quantum TD** » Sat Dec 05, 2009 3:33 am

P.S. If your pressures are not perfect, it should run pretty good. I just worked on a Rabbit pickup that had a WUR running at 40 PSI. I adjusted it with an exhast gas analyzer in hand until it ran at the proper Fuel Air Ratio. But I wanted it perfect, so I installed an old WUR, that had been rebuilt but was dirty inside. I pulled it apart, cleaned it, blew it out with an airhose, put in in the truck, and boom: perfect 52 PSI. It should be noted that that resistance on the unit was perfect.

The point being, I had the truck running really smooth, but it was running rich. That's why I fixed it. If you live in cold weather, a car that's running a little rich is a good thing. Easier starts and smoother running. You lose MPG though and can damage the cat.

Let us know what you find out about fuel pressures (i.e. give us numbers) and we can go from there.