1978 911SC CIS high pressures

[twaldron]

A little background. I've owned the car since '94-95. It's always been a pretty trouble free Sunday driver. In the last 10 yrs, it's done a lot of sitting as I've been involved in a frame off restoration of another vehicle, and family life. It has sat, un-started for the past 3 yrs when a brake caliper seized on me. I am now sowing the results of that inactivity. In the past couple of months, I have done the brakes (calipers, MC, booster, hoses, pads), new shocks/struts, new fuel pump (old one was loud), new fuel filter, etc etc.

I may have several issues.

Upon starting it, it will crank up, then die immediately. It will do this 3-4-5-6 times before beginning to awkwardly stumble and backfire through the air box, and slowly begin to run, very roughly, frequently stalling. After warming up awhile, I could get it to drive, barely. I put a 16 oz can of Seafoam and fresh Chevron Techron in it and got it on the hwy for a couple hundred miles with some minor popping under load (hill). Next day, same ritual, from A-Z.

Stats: US 1978 911SC, stock. 045 WUR

Tests so far:
Cold System pressure 4.8-4.9 bar
Cold Control pressure instantly bangs back to 4.8-4.9 bar. (yikes)
Warm Control pressure 4.8-4.9 bar. (yikes again)
Leak test after 10 min - 1.3 bar, after 30 min - nearly zero

I am getting 12v to the WUR when running, but that doesn't help the cold Control pressure anyway. I don't think the WUR is supposed to get power with key just to ON, but it does, albeit low. It starts around 10.5v and slowly creeps up to 11.3v one tenth at a time. However, if I crank the engine on, it hits 12.5v quickly. Confusing but probably a separate issue, lucky me.

I'm starting to suspect a fuel return line blockage, but before I start down that path, is there anything else I can check on the back end of the car?

Full disclosure: The fuel pump comes on as soon as the key is turned to ON and it will run indefinitely. I was going to start with that issue, but it's kind of been handy for the pressure testing since I just need to turn the key to get the FP humming.

[boyt911sc]

The return flow from the WUR is restricted or blocked. That is the reason you have the cold control and system pressure at same value. A good working WUR is what you need to correct the problem.

Tony

[twaldron]

Hi Tony, many thanks for the reply.

If I understand you correctly, the WUR itself is malfunctioning and the restriction/block isn’t, say in the gas tank return? Is there something I can do to to the WUR to save it? So I understand this, how is the WUR blocking the return fuel?

I did fill the WUR up with Seafoam overnight, but there was no change in behavior.

[boyt911sc]

Originally Posted by twaldron

Hi Tony, many thanks for the reply.

If I understand you correctly, the WUR itself is malfunctioning and the restriction/block isn’t, say in the gas tank return? Is there something I can do to to the WUR to save it? So I understand this, how is the WUR blocking the return fuel?

I did fill the WUR up with Seafoam overnight, but there was no change in behavior.

twaldon,

Disconnect the WUR’s return line and test run the FP for 3 sec. and read the control pressure at the gauge. If the control pressure remains the same as the system pressure, you have a blocked WUR outlet or return.

Tony

[twaldron]

Will try that next, thank you!

[Alan L]

Agree with Tony.
The WUR needs dismantling. May have crud on the disc or there is a fine screen in there.
The symptoms you describe also suggest lean mixture (high WUR pressures).
Alan

[gomezoneill]

There's a tiny screen that can get blocked buy debris such as rust etc...

[twaldron]

I had cleaned the screen previously with Seafoam as best as can be done from the top.

So what I’ve since done to try and definitely rule out the gas tank, is to leave the gauge connected to the FUEL distributor and connect the other side of the gauge set directly to the fuel line running to the gas tank, completely bypassing the WUR. I got the same System pressure of 4.9 and when I threw the lever to open up the gauge to the Control side, pressure dropped to ZERO. This seems to confirm that the line to the gas tank is clear and the problem lies within the WUR unit itself, as most of you are saying.

[boyt911sc]

Originally Posted by twaldron

I had cleaned the screen previously with Seafoam as best as can be done from the top.

So what I’ve since done to try and rule out the gas tank, is to leave the gauge connected to the FUEL distributor and connect the other side of the gauge set directly to the fuel line running to the gas tank, completely bypassing the WUR. I got the same System pressure of 4.9 and when I threw the lever to open up the gauge to the other side, pressure dropped to ZERO. This seems to confirm that the line to the gas tank is clear and the problem lies within the WUR unit itself, as most of you are saying. Make definitive sense?

With your current set-up (no WUR), adjust the valve to read 2 bar (cold control pressure) and start the engine. Your engine should start and if it does not, you probably have unmetered air going into the system. Do not run the engine too long just a minute and stop. Give it a try and keep us posted.

Tony

[twaldron]

I welcome a test for unmetered air, however, I’m not following. How do I adjust Control pressure to 2 bar without a WUR?

[twaldron]

Any reason I can’t open up the WUR and drop it in a gallon can of Chem Dip carb cleaner overnight? Rubber seal maybe?

[Alan L]

Originally Posted by twaldron

I welcome a test for unmetered air, however, I’m not following. How do I adjust Control pressure to 2 bar without a WUR?

What Tony is say is crack the valve so the pressure drops from 4.8 to 2 bar. Approximating what the WUR should be doing. Then see if it runs OK for a start up. If it does - it confirms as we have been telling you.
The WUR needs to be opened. Dropping it in a bucket of something is not going to remove the crud - it will still be in the WUR. And you have electrics in there too.
If you are not keen - maybe you can send it to Tony - if he is not too busy.
Alan

[twaldron]

I’m on the same page now, sorry for being a bit slow on cracking the valve!

And yes, it sounds like I better put a more gentler cleaning method to use. I had forgotten about the electrical portion as I was considering dipping options ala a carburetor. Once I opened it I would have nixed that idea.

As long as I don’t change the position of the pin, it will remain in calibration, correct?

[Alan L]

Correct - in theory.
But I am guessing crud on the disc. If the screen is clean.
But they are not that hard to recalibrate if it ends up out of spec.
There are threads on here on how to make them adjustable also.
Alan

[Alan L]

The pic you posted - which for some reason isn't showing up here, is the non-fuel side of the WUR. You need to get in to the other side.
Alan

[pmax]

Chemdip would dissolve that little o-ring under the diaphragm.

Some good stuff here if you haven't already seen it.
http://b2resource.com/PDFs/wurservicing.pdf

[twaldron]

Yes Alan, I realize that. it was an awkwardly crafted post on my part. I know I need to get into the fuel side yet. I was trying to make a comment on the age and condition. It looks pretty pristine inside but my brain and hands were doing different things so I immediately deleted it. .

Thank Pmax! I had read that pdf last week, but couldn't find it last night, so thank you for posting it.

[pmax]

I would go to town on that WUR Open it up and see if you can rebuild it yourself with one of the kits sold everywhere. It could just be one O-ring and some cleaning away from being back in service.

[theiceman]

so if your control pressures are too high because someone banged it in previously before you owned it, ( i can see the the punch mark , how do you know how far to bang it back out ? is it an order of magnitude in thousandths of an inch or mm ?

[twaldron]

The big problem I’m having right now is that the screws holding the discs are stuck and wanting to cam out. I have them soaking in PB Blaster, which I needed to get the case open. So far the only thing that has given has been the soft screw head.

Screws finally let go. Outlet hole blows clear but the Inlet hole doesn’t. Letting some carb cleaner sit in a pool above the screen hoping it will eat its way through.