WUR Help!! (long)

code7rpd · 06-17-2006, 04:48 PM

My SC (just rebuilt as a 3.2 SS, sport cams, and SSI's) backfires a little when cold for about a minute. During that time if I accelerate the car hesitates and does not want to go. After about a minute it runs with no problems. The mixture has been adjusted so that the CO is at about 1.00. When it was at .08 it would buck and backfire more.

I decided to check the fuel pressures and this is what I got:

At ambient temps of about 95 degrees when I have the valve on the tester off with the engine off and fuel pump running I get 0 fuel pressure. With the valve in the on position under the same conditions I get 53 psi.

If I have the engine off, valve off and the WUR unplugged I get 19 psi.

The cold pressure is 41 psi and the warm pressure is 49-50 psi. If I close the valve the pressure drops from 49-50 to 25 psi rapidly and then continues to drop slowly which does not seem right.

I thought that the control pressures were just a little low so I knocked the pin on the WUR in and it went in about 1/4 of inch before the car died. It seemed as though pushing the pin in caused the pressure to drop not increase. I took that WUR apart, pushed the pin back, and upon staring it I had 50 psi. I knocked the pin in and after going in over a 1/4 of an inch there was no difference. Incidentally, when I pushed the pin back after taking apart I set the pin flush with the housing but after knocking it in more that 1/4 an inch there is no change.

For residual pressure I have found that if the valve is open the pressure remains constant but if closed the pressure drops to 16 psi, according to the bently manual, the test is supposed to be done the the valve closed. If the valve is closed, the residual pressure drops to 16 psi rapidly which is out of spec.

What do these results mean? I am really confused.

boyt911sc · boyt911sc's Garage

code7rpd,

What's your system pressure (fuel pump)? You should have atleast 60 to 65 psi from your fuel pump (cold). Measure your fuel pump delivery pressure (cold) and see what pressure you have.

Tony

1982911SCTarga · 06-17-2006, 05:47 PM

I'm not sure what type of a gauge setup you've got and how you hooked it up, but I'll try to help.

Quote:

At ambient temps of about 95 degrees when I have the valve on the tester off with the engine off and fuel pump running I get 0 fuel pressure. With the valve in the on position under the same conditions I get 53 psi.

If the 53 PSI that you're referring to here is your "system pressure" -- engine cold and not running, fuel pump running and with the test gauge set to read fuel pressure with the WUR (or control pressure regulator) taken out of the equation, it might be low. Again system pressure looks at everything outside of the WUR or control pressure regulator. My Bentley SC manual indicates that your system pressure should be between 65 to 75 PSI (4.5 to 5.2 bar). This would affect the cold and warm control pressure tests that follow.

Also, with your cold control pressure check (WUR electrical connection unplugged, fuel pump running and engine not running), you need to look at the correct chart to see where you're at with the pressure you get. There are four different temperature/pressure charts depending on the year and the WUR part number to refer to in the Bentley manual.

One more thought. With your 3.2 build, you might need a slightly higher control pressure. The engine and CIS gurus can chip in on that one.

Don't be in a rush to knock the plug, make gross adjustments, etc. Work carefully and thoughtfully.

You want to know three things: system pressure; cold control pressure and warm control pressure. Hope this helps.

Brian

code7rpd · 06-17-2006, 07:07 PM

Thanks for the help guys. My system pressure shows zero with the engine off, fuel pump on, and WUR taken out of the equation. With the valve on the tester open, which includes the WUR, the system pressure is 53 psi. I know that doesn't make sense but without fuel going to WUR it reads 0 psi.

The tester runs from the fuel distributor (line that goes to the WUR) and the other end goes to the WUR (the other end of the line which was disconnected from the fuel distributor) and in the middle is a T fitting with the guage. The T fitting has a lever which controls fuel going to the WUR - with the lever closed I get 0 psi for system pressure but with it open I get 53 psi.

code7rpd · 06-17-2006, 07:11 PM

Also, with the engine not running, fuel pump running, and WUR unplugged with the engine cold I get 19 psi.

code7rpd · 06-17-2006, 07:17 PM

The the other thing is that with the car warm, WUR plugged in, engine running, with the valve on the tester closed to take the WUR out of the loop the pressure rapidly drops from 50 psi to 25 psi. It then slowly continues to decrease to about 15 psi.

code7rpd · 06-17-2006, 07:58 PM

I think I will do the tests again tommorrow - I must have done somethign wrong.

code7rpd · 06-18-2006, 08:11 AM

I tried the tests again, after realizing the gauge was hooked up wrong, and got a system pressure of 68 psi. The cold control pressure was 13 psi and warm pressure was 50 psi. How do I get the cold pressure up?

1982911SCTarga · 06-18-2006, 08:22 AM

If you've got your gauge correctly installed for doing the tests, your system pressure looks good. Now focus on what your cold control pressure readings are telling you compared to where they ideally should be.

I just picked up a Bentley manual for 1975-77 VW Rabbits and Sciroccos at a used bookstore for $1 this morning. There's a good section in this book on Bosch CIS systems theory and troubleshooting (including charts that aren't in the Bentley Porsche SC manual). Another good future reference.

Brian

code7rpd · 06-18-2006, 10:37 AM

I have the Probst Bosch Injection manual which details things pretty well but I didn't see anything in there regarding what would cause, and how to correct low cold control pressures.