Do I have a WUR problem?
 

Hello everyone,

Wondering if someone can help me here.

'79 SC

Symptoms:
1) Very difficult cold start - backfiring from exhaust - sputtering, etc. Warmer weather makes it easier to start.

2) missing under load - bogs down - as though running on 3 cylinders

3) No issues with restart when warm

I tested the following, using a CIS pressure tester:

Fuel pump pressure (WUR isolated): 68 psi
System pressure (with WUR) : 68 psi (same as fuel pump!!!!)
System residual pressure (upon shut down from warm - with WUR of course): Holds at 25 psi for a while but stabilizes longer at 20 psi. Eventually drops, below 20 psi, but very slowly.

These numbers were different in the distant past. I believe system pressure should be closer to 45 psi if the WUR is doing its job. no?

Is there something I can do to rebuild or adjust the WUR? Any thoughts would be greatly appreciated.

Thanks in Advance
Tarek
'79 sc

A high control pressure will make it run lean, hence your popping and missing and bogging. In your case, it's running very lean! The pumper has to work against that 68PSI..as oppose to a 45-50 psi when warm. W/o proper plunger travel, you won't get enough fuel into the cylinders.

Be careful you have not cracked your airbox with all that popping.

You can try to clean the WUR. There is a screen at the inlet to it. If that screan is clogged, you will not flow through the WUR as you should, and thus the control pressure will be the system pressure.

Clean it...then try again.

Thanks Souk. I did forget to mention that the car sat for a few months and I used a lot of Berryman cleaner in the tank (for no particular reason...just thought I was doing a good thing) when I put it back on the road.

I have the pop-off valve installed in the air box. No cracking that I could see.

Do I need to remove the WUR for cleaning or is the inlet screen accessible in the mounted location?

Thanks a bunch
Tarek
'79 sc

Hey T

Sounds almost like my car a few weeks ago, replaced WUR and no prob after that, I have a link for rebuilt ones that save you money email or pm me if you want it.

Todd SmileWavy

The control pressure needs to be lower (25-30) psi at cold start up and then rise to the 40-45 when warm. Thats the WUR s job. Check for more specific pressures for your car year and model. Definately sounds like the WUR.

System pressure = test gauge valve closed = WUR isolated out of the circuit

Control pressure = test gauge valve open = WUR dependent

POST WAS EDITED FOR ACCURACY FOR FUTURE CIS SEARCHERS

I had the same problem about 2 months ago...the exact same problem. Everyone here gave me hell for replacing it but I went through all the motions....I had the entire car checked out. Mine is a 74 911. In the summer it ran beautiful, however when winter hit, the car started like crap in the morning and later in the day if it sat, it ran like it was missing a cyl and when I hit the gas it bogged down. So I replaced the WUR and guess what??!!...It ran perrrrfect and started perfect too. My mechanic said excellent job because he had checked everything else and told me the same thing everyone else did on this site....it's probably not the WUR...but it was.

Thanks Todd. Yes I would love to consider rebuilding the WUR if the problem is narrowed down to it. Please send teh link. Thanks again
Tarek

Hi Scott,

The pressure goes straight to 68 psi quickly upon start (when it finally starts) when the car is cold. Is that what you meant by cold start up?

Thanks
Tarek

Elu,

It seems that most people here are agreeing my WUR is the culprit. The question remains if simple cleaning of the screen, rebuilding, or buying new is required

Thanks again
Tarek

Clean the tank out (drain it), replace the filter, flush the the system.

Take the WUR off and clean it. Flush it with carb cleaner (flush back wards).

It's obvious you have a blockage somewhere in your system, likely the return to the tank, which can occur through the WUR or the fuel distributor regulator.

Start at the WUR. It's easy to get out and it'll you for sure if you have a blockage there.

Do fall victim to the "replace parts until you fix it" thinking. The problem has been identified...now find address the cause.

Same issues on my 1973.5T. Unfortunately I have one of those original WURs that are half the size of the one's on the '74 and cannot be rebuilt or cracked open! My cold start pressures seem to be okay, but once in the warm zone it stumbles and sounds like its starving for fuel. Every other CIS component has been replaced!! I am now awaiting a rebuilt unit that replaced the original that the seller claims is preset and should be fine. I cannot wait to get tyhe darn thing already.

I am sure its a WUR issue, but you might want to check out some other components as well (termotime, cold start valve, and CO setting) if the WUR is not the issue.

Bob
73.5T

Hey again,

Definately do as Souk suggests before doing anything else,

I too am not a big " replace it till it's fixed " person either , so do the free stuff first, like the cleaning and what not,

If you still need to go the way of a Rebuilt WUR you might give these guys a shout, I have had really good luck with their stuff.

http://www.specialtauto.com/porsche-parts/

THIS IS IN NO WAY A SLIGHT TOWARDS OUR HOST AS HE DOES NOT SELL REBUILT WUR PARTS TO MY KNOWLEDGE AND IF I AM MISINFORMED WOULD A MOD PLEASE REMOVE THIS PART OF THE POST.

I FULLY RECOMMEND PELICAN PARTS FOR ALL YOUR NEW PARTS NEEDS.

Todd SmileWavy SmileWavy

Tarek,

Your WUR may just be out of adjustment. If you search "knocking the plug" you will see a lot of info on adjusting the control pressure. You can do this by just knocking the plug on the top of the WUR down which lowers the CP and richens the mixture, and checking the pressure again w/ the fuel gauge. Or you can make it more easily controllable with a little bit more effort.

If your car was built through Dec 78 your cold cp should be about 1.6 to 2.05 bar @ 10C. If built in Jan - Aug 79 the ccp should be1.5 to 2.0 bar.

Fuel pressure terminology conventions
 

Just so things aren't confused when speaking of fuel pressures, there is system pressure and there is control pressure. The system pressure never changes. It is the pressure regulated by the internal regulator of the fuel distributor, and is ideally about 72 psi. The control pressure on the other hand is that regulated by the WUR, or in the case of the cars up through '75, the WUR and the throttle contol pressure regulator. When the control pressure regulator (WUR in the case of '76 and later cars) is blocked, the contol pressure rises until it matches system pressure.

As Souk noted, the blockage could be anywhere in the WUR fuel circuit: the line to the WUR, the WUR itself, or the line from the WUR to the fuel return back to the tank.

Tarek,

From your description in your beginning post, it wasn't clear that you measured control pressure, as you noted "fuel pump pressure" (to me implies a measurement at the fuel pump side of the FD), and "system pressure" (implies pressure measured in the control circuit, but with the pressure guage valve closed). Then "control pressure" would be with the valve open. But since you didn't list a control pressure, I was a little confused as to what you measured. These terms are just convention, but they help in knowing what was done when "troubleshooting by email", so to speak.

Jim,

Thanks for the clarification. I guess I was using the wrong convention.

Here are the developments:

Got warmer, much warmer here, so I tried it today and the car started ok. Rough idling, and some backfiring, but far from the excessive sputtering and backfiring in the cold

I removed the WUR and opened it up and cleaned it. There was some sand here and there, but nothing major in my opinion. I put it back together and installed. Car started the same. Rough and some sputter, but it held, just like just before the WUR cleaning. Certain to backfire if you blip the throttle.

Pressure readings remain the same as before: 68 psi at the gauge, measured between Fuel distributor and WUR. Same reading with valve open or closed. According to Jim, system pressure and control pressure are the same.

So th eonly improvement is related to weather as far as cold start. Haven't driven it yet to see if it would bog down under acceleration, but I think I should not expect an improvement there.

What's next? clean up the fuel distributor? how involved is it? new fuel filter is on order

thanks in advance
Tarek
'79 SC

I've gone through at least 6 or 7 tanks since the problem started. Is it still necessary to flush the tank? I will replace the filter when it arrives, but was just wondering if flushing the tank is necessary, given that I've gone through so many fill ups already. Should I be looking for a plug at the bottom of the tank, or is it normally flushed at the fuel pump inlet?

Thanks
Tarek
'79 SC

Are you saying that your WUR control pressure never changes? You should have the WUR electrical connection unplugged on a completely cold engine. Start the car and check the pressure, it should be like 30PSi or so depending on the year, then you plug the WUR in watch it rise to the operating pressure around 50psi. If you're never getting a change then the heating element is probably shot. You should have 17ohms measured across the element.

Scott,

I measured 23 ohms across the element (plug). Starting from cold with the plug disconnected yields 68 psi immediately. No changes when the plug is connected

Thanks
Tarek
'79SC

Tarek,

If there is no difference in the pressure guage reading with the valve open or closed, and all the pressure guage hoses are properly connected, you definitely have a problem in the WUR fuel circuit. Something is plugged up. With the valve open, and a cold WUR, pressure should be 25 to 30 psi. With a warm WUR, pressure 40 to 45 psi. The WUR control pressure should never read the same as system pressure, regardless of whether the WUR is cold or warm.

For a quick test, get the fuel pump running and crack the banjo fitting on the WUR leading to the fuel return line. Do this slowly so if you do get some fuel flow, you can retighten the connection with out excessive fuel flow. Have a rag handy to catch the fuel. If you get some fuel flow, and have the pressure guage connected and an open valve, you should notice the pressure drop slightly. If you get no flow, the WUR is likely plugged. If you do get flow, the return line is likely plugged. Now try the same technique with the connection at the WUR from the FD. Remember, just crack the connection intially. If you get fuel at this point, you can confirm the WUR is plugged.

It will read 23~24 across the terminals even if the element is cooked, that's the resistance of the wiring and the plates inside, you have to check across the terminals on the element itself.

I will however say this, I'm sitting on four bad WUR's (with bad elements) and all of them have visual indications that the heating element is bad, on two the green ceramic coating is falling off, and on the others the wiring to the element is melted.

With the high pressure in your system it almost seems like the diaphram is stuck however. You can send it to:

http://www.fuelinjectioncorp.com

They can test it and make any repairs required, good guys, and fast turnaround.