Fuel pressure testing. System pressure = cold control pressure, residual press = 0

[david05111]

Hey gents-

I have an '80SC that I've been trying to get running for a while. It's now running - sort of -, having gone through a complete top-end and CIS rebuild. The shop that did the work lost a few good techs, and I'm not sure they really know what they're doing beyond re-assembling stuff, but they got it running. Since it had a lot of idle surge, I decided to start tracking down what's going on. After eliminating a few vacuum leaks, I bought a CIS fuel pressure tester kit (33800) and decided to have a go with it tonight.

The system pressure reads 4.95 BAR/72 PSI which is in-spec. No issue there.

When I went to check the cold control temperature though, absolutely nothing changed. When I opened the valve and allowed fuel to flow to the WUR, the pressure didn't drop a single bit. I think I can hear fuel returning to the tank (maybe?), so the return line is getting fuel, but the actual fuel pressure is still like 4.95 BAR on a cold regulator. I didn't even try plugging it in; seems there's little point in doing so, at the moment.

As I understand it, where these WURs usually go wrong is in the heating element. I've heard of cases where the element is shot and therefore the pressure never rebounds, but in my case, it seems there's something causing my pressure to be really high from the beginning. I expected the cold pressure to drop to like half of what the system pressure is (say 2.4 BAR), but it never budged.

What could cause this? I thought maybe the return line was clogged, but I can hear fuel returning to the tank. I'm not sure how else to test that. I know there's a screen/filter in there as well, which I'm inclined to check.

What else should I be looking at?

Another issue is the residual pressure bleeds REALLY quickly. Basically as soon as you shut off the pump, it starts to drop. It drops almost immediately to around 1.2BAR, then arrives at zero in about 40 seconds.

I don't even know where to begin on that. I could use any input you guys have.

I haven't removed the WUR from the car yet, so I don't have the part number on it.




Just as an aside, the car no longer runs lambda; the o2 sensor was eliminated.

Also, the top of the WUR has a vacuum port that has nothing connected to it. I've done a little bit of reading and it looks like it's not necessary, but it's not capped or anything. There's also nothing that I can tell that's supposed to be connected to it in the engine bay, though I could look more thoroughly if someone could point me in the right direction there. We tested for vacuum leaks and corrected the ones we found.

[andino]

What's the 3 digit code on your WUR? 80sc shouldn't have a vacuum port on the WUR so you may have the incorrect WUR. The 80sc WUR is unique to that year only iirc from my research. I also have an 80sc but I could be mistaken as I'm still learning about the car as well.

[E Sully]

The WUR should be 0 438 140 072, and would not have a vacuum line connected to it.

[david05111]

Originally Posted by E Sully

The WUR should be 0 438 140 072, and would not have a vacuum line connected to it.

Thanks, I have the Bentley manual for the car and found that data. The system pressure is fine; the rest isn't (didn't test the warm pressure).

The WUR has a bung for a vacuum line, but nothing is connected to it. I'm going to head over to the garage and pull the WUR out of the car to get the part number off it. I haven't done enough reading on the subject, but I remember seeing it mentioned somewhere that you could basically just cap that off and it would be fine.

I honestly don't know what function the vacuum line plays on the WUR anyway

[boyt911sc]

David,

If your car is ‘80 CIS US spec., the warm-up regulator would be WUR-072 and fuel distributor is FD-077. Check and confirm them before proceeding to troubleshoot your problems.

For the cold control pressure to get as high as the system pressure, the culprit is your WUR or its return line is restricted (clogged).

Tony

[david05111]

Originally Posted by boyt911sc

David,

If your car is ‘80 CIS US spec., the warm-up regulator would be WUR-072 and fuel distributor is FD-077. Check and confirm them before proceeding to troubleshoot your problems.

For the cold control pressure to get as high as the system pressure, the culprit is your WUR or its return line is restricted (clogged).

Tony

I'm going to pull the WUR to have a look at it and get the part number. Where is the part number located on the fuel distributor?

[david05111]

Ok, pulled the WUR from the car.

Firstly, it is the correct part number: 0 438 140 072. That’s good news. A few observations:

- The return line has a connection on it that I’ve never seen before in any of the literature. See attached. It’s a flexible line with sort of a cone fitting that slides over the port in the WUR and is secured with a bolt with ports in it that allows fuel to enter the line.

- The ports on the WUR look rusty. That’s not entirely surprising; the engine underwent an overhaul after the car had been sitting for 25 years. While the main hard lines coming out of the distributor were replaced with flex line as part of the overhaul (along with a new fuel tank), it looks as though the shop didn’t replace the WUR or the return line. As a result, I’m guessing both are pretty gummed up.

How to fix that, I’m not really sure. The WUR looks like it's a short fuel path. I could probably replace the fitting on the top of it hit the area that fuel runs in with some carb cleaner. The line is another story. I had a look at the path of fuel in the Bentley manual. It looks like there's a a main return line from the fuel distributor and there's a smaller line that runs from the WUR and connects to the main return line. I'm not sure where the issue in the line is. I sort of suspect that the main line has to not be totally blocked. Can the car run and drive if it is blocked? I'd be surprised. That sort of makes me think that the line from the WUR to the main line might be jammed up; at least that being jammed wouldn't keep it from running. I haven't a clue where that line goes though...it's hart to follow it's path in the engine bay. I assume the fuel lines run underneath the car, so I suspect that the junction for the return is somewhere accessible.

Regarding the WUR, I obviously can't test it like the manual suggests at the moment since the pressure is so high already. Is there any other way to reasonably tell if the element inside is working? For instance, can i plug the thing in for 10 minutes and touch it? Would the casing get hot enough to notice if it's working?

It seems like the main issue with these is the element. If the element is fine, the rest can be serviced. If the element is bad, you have to basically send it off and get a refurb.

[david05111]

Just a follow-up. I grabbed the part number off the distributor and it looks correct.

0 438 100 077

[pmax]

Originally Posted by david05111

Yep, looks cruddy indeed.

There's a debris screen under that adaptor which is likely clogged. The rest of your system could be similar, take a peek into the fuel tank, change out the fuel filter if you haven't already.

[david05111]

Originally Posted by pmax

Yep, looks cruddy indeed.

There's a debris screen under that adaptor which is likely clogged. The rest of your system could be similar, take a peek into the fuel tank, change out the fuel filter if you haven't already.

I'll take that adapter off and see what I've got underneath. If that's the issue, that would certainly be nice.

I know the fuel tank is good to go; it was replaced recently since the old one was a mess. Fuel filter has also been swapped. I don't think the return lines (and maybe not the feed lines either) were replaced though.

It does look cruddy, that's for sure.

[david05111]

Another small update.

I tested the WUR with a multimeter. The good news is that it isn't dead. That said, the ohms definitely read low. It's reading about 9.3-9.4 ohms in a 70 degree room, or thereabouts.

I found this thread that talks a little about the 072 WUR. It looks as though the port on top isn't for vacuum; it's a vent. Unfortunately, it's supposed to have a down-turning vent hose on it and it doesn't, so hopefully it hasn't let a bunch of junk in to screw it up.

The guy in that thread also had an ohm reading on his of around 9.4. That gives me some heart, because his ran as well.

Can anyone give me an idea of the physical path of the return lines and how I might go about best dealing with those? Maybe best to disconnect all of them, blow some compressed air through or perhaps use a straight rod to sort of poke around in them?

Not really sure how best to proceed.

[PeteKz]

Yeah, that's pretty cruddy. I strongly recommend you disassemble and clean it out before proceeding.

Hose routing. The control pressure line goes from the middle of the FD to the threaded nipple on the WUR. The return line goes from the banjo bolt on the WUR forward to the return line to the tank. It T's into the hard return line at the front left of the engine.

The vent nipple on the top of the WUR should have a hose that goes to the topmost nipple on the back of the throttle body. It's between the top of the airbox and the throttle body.

[pmax]

Originally Posted by PeteKz

...
The vent nipple on the top of the WUR should have a hose that goes to the topmost nipple on the back of the throttle body. It's between the top of the airbox and the throttle body.

The link above is correct, it isn't a vacuum hose just a vent of some sort to atmosphere. If I'm not mistaken, the 072 in the 80, have one as well, is a "special" in this respect.

[david05111]

Originally Posted by PeteKz

Yeah, that's pretty cruddy. I strongly recommend you disassemble and clean it out before proceeding.

Hose routing. The control pressure line goes from the middle of the FD to the threaded nipple on the WUR. The return line goes from the banjo bolt on the WUR forward to the return line to the tank. It T's into the hard return line at the front left of the engine.

The vent nipple on the top of the WUR should have a hose that goes to the topmost nipple on the back of the throttle body. It's between the top of the airbox and the throttle body.

By disassemble and clean, you mean the WUR, right?

Do I risk screwing up factory calibration of the unit if I take it apart? Or does it all basically stay where it needs to be?

[pmax]

Originally Posted by david05111

By disassemble and clean, you mean the WUR, right?

Do I risk screwing up factory calibration of the unit if I take it apart? Or does it all basically stay where it needs to be?

The CPs is the calibration. In fact, many make these adjustable, I have one, to tune the CP when it goes out of spec. CIS Troubleshooting for Dummies

It's controlled by a bimetallic strip with a heating element pressing down on a "sombrero hat" against a mild spring adjusting the pressure via a pin on a diaphragm. The 072 being lambda controlled doesn't have a vacuum section so it just has a single compartment with the above inside. I don't think you will screw anything up by removing the cover and checking if things look good inside, nothing burnt, diaphragm's intact etc.

[PeteKz]

Yes, the WUR. You won't screw up the calibration--it's already screwed up! Unless you rip the internal diaphragm, you will improve its operation. The 072 WUR might not even have an internal diaphragm because it does not have a vacuum function (Tony or someone else can verify).

Take it off the engine, then remove the screws that hold the top and bottom together. Carefully separate the halves and take care that you don't tear or puncture the internal diaphragm. Internally, it's pretty simple. Clean everything with a mild solvent, like kerosene or WD40. Pay special attention to the very fine screen at the inlet to the WUR and get any crud out of it with a fine brush, air pressure, whatever. But if you use air pressure, make sure the screen doesn't fly out and hide somewhere in your shop.

When you are satisfied that the internals and fine screen are clean, put it back together and re-run your CCP and WCP tests. Since you don't have the fancy setup that Tony does, you will have to check it on your engine.

Check the return line too and blow in it to make sure it is clear.

Report your results here.

Residual pressure loss: Since your CCP is the same as your SP, that indicates that the WUR is completely blocked, so that's probably not where you are losing RP. 3 other parts seal RP: The SP regulator valve on the FD, the Fuel Accumulator (FA) and the fuel pump check valve.

FA: Very common for the internal diaphragm in the FA to be leaking after this many years if it's still the original FA. To test, run the pump and disconnectt the bottom fitting (return line) from the FA. If you get fuel running out, it's bad. Replace it with a new one.

Then retest your residual pressure. If it's still losing pressure, then most likely the check valve is leaking. To test for that, pinch off the rubber line that goes from the return hard lines on the engine to the firewall, then re-pressurize the system and turn it off. If it still loses RP, then the check valve is bad. If it doesn't lose RP, then either the SP regulator valve or WUR is leaking. Then turn the valve on your gauge set to measure SP and recheck RP loss. If you still lose RP, then the SP regulator valve is leaking. If you don't lost RP, then the WUR is leaking.

[E Sully]

You would want to re-calibrate after rebuilding. You can take a look at the K Jet Specialists manuals to get some idea of what is involved.
https://k-jet.biz/rebuild-manuals/

[david05111]

Been sick for a few days. I forgot to post this the other day. The screen on the WUR had *some* gunk in it. I cleaned it up a bit.

Is a partial blockage enough to cause the pressure to be equal? Or is this not enough of a problem to explain what’s happening?

[Alan L]

That looks completely blocked - it is not the large bits that are the problem. The mesh looks clogged.
You can remove it. CAREFULLY. Don't go sticking a sharp object in there to fish it out.
Try blowing it out from the other side (inside). On to something like a rag. As PeteKz says - don't loose it on the other side of the shed. Then soak it in kero, brakekleen, carb cleaner etc.
You could try soaking/cleaning without removing it - but you are still going to flush the other side to get the gunk out.
Alan

[boyt911sc]

David,

I will be back home in a week after traveling through Netherlands and Belgium. I have several WUR-072 that have been rebuilt and calibrated. More than happy to lend you one that you could test in your car. No obligation to purchase. Send it back to me. No question asked. Your only expense will be the shipping cost. Think about it and PM me your decision.

Tony