Fabio421

I've got some issues with my CIS so I bought a test gauge kit. My control pressure is too low and it never gets lower as the system warms up. The The max system pressure is also too low ( 35psi ) and I can't get it to go up. I took the system relief out of the fuel distributor and it appears to be clean and with proper movement. It appears that you shim it to raise spring pressure. Since I didn't have any shims I stretched the spring a little. It didn't make any difference.

I'm thinking that the pump may not be working properly since I can't achieve system pressure. But the fact that the control pressure never changes makes me wonder whats up with the WUR. I took the WUR apart and everything appears to be in good order. The diaphram isn't leaking and the plunger moves. So why isn't the control pressure dropping? Hmmm?

I also have a question about the vacuum ports on the WUR. My bosch CIS book shows that an early WUR should have the small port at the bottom only and that the later WUR's have the larger vacuum port on top in addition to the small one at the bottom. But the description it reads like only one would be used. On the 928, are they both used? If so, what is the correct location to hook up the other end of those vacuum hoses?

GlenL

How are the pump and filter?

Fabio421

Filter is new. Screen in the WUR is clean. No screen in the fuel distributor .

As I stated above. I'm wondering if the pump may be weak.

Is there an adjustable fuel pressure regulator on a CIS car?

GlenL

The pressure regulator is at the fuel distributor. Sounds like you've tried that.

Do you have the warm-up circuit? This is a solenoid over the right-side head. Maybe it's stuck ON and lowering the pressure. It's a bit of a mystery device as it's not well documented.

SMTCapeCod

System pressure is the spring and plunger assembly that you pulled out of the FD.
There are a bunch of different Bosch fuel pumps for various applications- they have basically the same housing but operate at slightly different pressures, might due to make sure that you have the right one in there.

If I remember correctly, tapping the metal disc that has the fitting for the fuel lines down into the body of the WUR raises the pressure...but it is a delicate operation fraught with risk if you go to far, and it still doesn't address why you aren't seeing anything during the warm up cycle. Have you checked the electricals?

Also if I remember correctly, the upper vacuum port provides enrichment when it gets vacuum during acceleration on Euro/RoW cars, but the CIS US cars it is non functional.
Its been a few years since I've gotten into the weeds on this stuff- a good place for you to start would be the landshark OZ page, they have a .pdf on CIS with some schematics of the warm up regulators on there.

SMTCapeCod

Here's the link:
http://www.landsharkoz.com/tt/ttwur.htm

The author and a few others (Dennis, Jim) with more advanced CIS skills still ping in from time to time, I'm sure we'll get to the root of the problem.

soontobered84

I had the same problem initially on the Jalapeno car. Turns out that the PO had replaced the fuel pump with one from an '83, which has substantially lower pressure. I'm sure you've already done this, but check your fuel pump part number to make sure you have the right one. Good Luck

GlenL

This is solid advice.

I'm surprised at the variety of pumps that are available and they all look alike. Why not one or two models? I guess it's easy to spec one that meets the rate/pressure needs and not installing a higher pressure/flow unit saves a buck or two.

Fabio421

Look what I found.

GlenL

The higher the control pressure the _leaner_ the mixture. Like they show in the vid, it starts with lower control pressure and then it goes up to give extra gas during warm-up.

karl ruiter

I would worry more about the control pressure than the system pressure.

If your control pressure is not changing over time then either your plunger is not working or the thermal element is not working. First I would check the wiring to the thermal element. Is the ground side grounded? Is the hot side hot? Then I would check the thermal element. Does it have reasonable resistance? If you hook up 12 volts to it (use a battery charger) I think you should be able to see it move as it heats up. If the thermal element has the correct signals and seems to move, then I would look at the plunger. Hook it up in system with the bottom off the regulator and activate the plunger with your finger. You should see the control pressure change.

If you want to change your warm control pressure you can do it, although the 928 WURs I have seen do not have an adjustment screw. There is a rod that goes between the thermal element and the plunger. You can modify the control pressure by changing the lenght of the rod. Get a piece of 1/16" brass rod from the hardware store, cut it a little longer of shorter than your old one and tune the length with a file to get the pressure you want. This process takes a while because you have to completly assemble and install the regulator each time you want to test your rod length. But it can be done, it will work and it costs about a buck.

You can always buy a rebuilt WUR, but they are expesive and last time I tried this the rebuilt unit I got produced control pressures that were nowhere close to spec, so I returned it and fixed my old one.

Fabio421

I have verified that the pump is correct. That doesn't mean its at full strength, but at least it's the correct part number. While I was checking that, I noticed that the inlet hose to the pump was kinked. It was kinked pretty bad. So muchso, that I think it was probably starving the pump in some cases. The hose was also 7/16" fuel line. I took it loose and drained the tank. I mic'ed the nipple at the inlet of the pump and it looks like it would use 1/2" ( or the metric equivelant ) fuel line, not 7/16". The local parts supply didn't have 1/2" FUEL line, 7/16 was the biggest they had. I bought 7/16" fuel line and 1/2" heater hose. Before anyone gets all up in arms. The 1/2" heater hose is just to test to see if that restriction is causing or contributing to my problem. I won't leave it on there, I promise. [/cross heart]

Why would you worry more about the control pressure than the system pressure? They both need to be correct for it to work correctly from what I've read.
I suppose if they were both equally incorrect and the pressure diferential remained the same it would still work, just not at WOT. Hmmm? I'll have to think about that.
When I took the WUR apart, the plunger was moving freely. I moved it with air pressure. I did not bench test the bi-metalic strip but in my opinion, the WUR will get hot and change pressures just by the WUR reg. heating up from the engine temp rising. The bi-metalic strip is there to raise the pressure sooner since the engine will get warm before the WUR and therefore not need as much fuel. I've ran the engine for 20 minutes without a change. I would assume that 20 minutes would be enough time for the WUR to warm up even if the bi-metalic strip isn't working. I'll check it this evening just to be sure.

Tampa 928s

Your getting closer

SMTCapeCod

I threw down for a new Euro WUR from one of the big three...and it was waay out of spec when I got it. I wasn't able to get it back into spec, so I sent that out to a commercial CIS shop to be adjusted. Well, originally the rebuilder said it would only be a slight fee to recalibrate, then...after a few weeks...he called with the news that it had already been rebuilt. That was all fun. Not.

jpitman2

There is a doc on benzworld showing how to calibrate a WUR...watch the wrap.
http://www.benzworld.org/forums/w126...libration.html
When you looked at system pressure, did you have the WUR side of the gauge closed off? If not, you will only see control pressure. There is some latitude in the pressures - I have seen system listed as 65-75 psi (mine is 75), hot control 40-45psi. System Must be over 65 because the injectors dont open until ~55psi. Is your flow rate OK ? 1360ml/30secs IIRC. If not, look at pump, filter, or hoses along the way. Control should start LOW (<20psi), and rise within 10-15 mins to final value. FWIW mine had an S4 pump on it when I got it, worked fine. Pretty much any injection usage pump should be able to deliver in any but hottest and highest load conditions.
jp 83 Euro S AT 52k