77 911s Fuel Pressures

[Avanti]

Engine requires 5 to 10 tries/cranks to start. Idles OK but sputters on rev up. Feels very lean which it is if I deciphered my pressures below right.


Control pressure: 70 psi
System pressure cold: 70 psi. (does not drop to mid 20s)

Connect WUR harness: Pressure stays at 70 from 0 to 5 minutes. However, needle quivers a little after 2 minutes and pressure goes up a couple of lbs. then no change.

Gauge hooked up correctly with shut-off valve on side of WUR.

Residual pressure little or none. Drops to 10lbs. in 40 seconds then to 0 after 1 minute.

WUR# 0438149 033 - Resistance cold is 27 ohms

This car sat for 18 years. Fuel tank, pump and filter are new. Check valve was not replaced (forgot to order) and accumulator bench tested OK and looked clean.

Figure I have two problems, the system pressure and residual pressure. Can one affect the other? Although the accumulator looked clean, could a frozen or gunked up WUR give pressures like this?

[boyt911sc]

Originally Posted by Avanti

Engine requires 5 to 10 tries/cranks to start. Idles OK but sputters on rev up. Feels very lean which it is if I deciphered my pressures below right.


Control pressure: 70 psi
System pressure cold: 70 psi. (does not drop to mid 20s)

Connect WUR harness: Pressure stays at 70 from 0 to 5 minutes. However, needle quivers a little after 2 minutes and pressure goes up a couple of lbs. then no change.

Gauge hooked up correctly with shut-off valve on side of WUR.

Residual pressure little or none. Drops to 10lbs. in 40 seconds then to 0 after 1 minute.

WUR# 0438149 033 - Resistance cold is 27 ohms

This car sat for 18 years. Fuel tank, pump and filter are new. Check valve was not replaced (forgot to order) and accumulator bench tested OK and looked clean.

Figure I have two problems, the system pressure and residual pressure. Can one affect the other? Although the accumulator looked clean, could a frozen or gunked up WUR give pressures like this?

Avanti,

Are you sure you have 70 psi. control fuel pressure? For the control pressure to be the same as the system pressure simply indicates blockage or restriction to the return line. Double check your gauge connection. System fuel pressure is measured with the valve closed and control fuel pressure with valve fully open. When you open the valve after checking the system pressure, the pressure should drop down. If it does not, either the gauge is defective or the fuel is not flowing freely back to the tank. A clogged WUR or return line would exhibit this type of problem.

Tony

[Avanti]

Tony,

Sorry, I had it backwards.

System pressure - valve closed is 70 psi.

Control pressure - valve open is 70 psi.

Gauge connections correct. New fuel lines in engine bay and tunnel lines.

Same pressures with different gauges. Right now I'm using a brand new one.

Is there a place between the fuel distributor and the engine bay return line that could be blocked?

Paul

[boyt911sc]

Paul,

You have fuel flow restriction in the system. It could be any where between the WUR and gas tank. With the fuel gauge connected, break the fuel return line from the WUR. Place the ends of the fuel lines in suitable containers to collect the fuel that might come out during the test. Test run the FP for a second or so just long enough to get a pressure reading at the gauge.

If the WUR is clogged or causing the very high control fuel pressure reading you will not get any flow after the WUR. If fuel is not coming out from the WUR (FP running and valve open) you located the culprit. Do this test and let us know what you find.

A very clogged or restricted WUR flow is like having the valve at close position. And with this condition, the control fuel pressure would be the same as the system fuel pressure.

Tony

[Avanti]

Thanks Tony,

Based on the many posts here on CIS problems it sounds like I have a not so common problem, but one that is quite possible on an engine that has not been run in many years.

I'll have time on Monday to do the checks you recommend and post my results. BTW, what are your thoughts on the residual pressure? Should I worry about that after I get the system and control pressures corrected? THX!

[boyt911sc]

Originally Posted by Avanti

Thanks Tony,

Based on the many posts here on CIS problems it sounds like I have a not so common problem, but one that is quite possible on an engine that has not been run in many years.

I'll have time on Monday to do the checks you recommend and post my results. BTW, what are your thoughts on the residual pressure? Should I worry about that after I get the system and control pressures corrected? THX!

Paul,

Your high control fuel pressure has nothing to do with your engine. It is the fuel flow restriction in the CIS unit. This is a common problem when using dirty or contaminated fuel or pinching the fuel return line preventing fuel flow. Investigate the fuel return line section by section to isolate the culprit. It is very easy and simple to locate where the blockage occurs. But it would be more fulfilling if you could discover yourself where the problem is located than spoon feeding you what to do.

Tony

[Avanti]

Tony,

Sorry you misunderstood. I wasn't clear.

Nothing wrong with the engine. What I meant was engines that haven't been used for lon periods have contaminated fuel systems, i.e. varnish, rust etc.

I've revived countless old cars but never one with CIS.

Thanks for all the suggestions so far.

Paul

[Avanti]

No blockage in the lines. No fuel from the WUR per your instructions above



Cleaned the WUR per this article. http://b2resource.com/PDFs/wurservicing.pdf

The WUR was not rusty and the screen was partially blocked. No change in pressures.

Can the WUR be taken apart further to clean other potential blockage? The author does not take apart the top part where what looks like a vacuum valve is.

[T77911S]

you need to confirm gauge connection. at 70psi CP i am not sure it would run.

the hose with the valve goes to the WUR.

if that is correct check the screen in the top of the WUR

[boyt911sc]

Originally Posted by Avanti

No blockage in the lines. No fuel from the WUR per your instructions above



Cleaned the WUR per this article. http://b2resource.com/PDFs/wurservicing.pdf

The WUR was not rusty and the screen was partially blocked. No change in pressures.

Can the WUR be taken apart further to clean other potential blockage? The author does not take apart the top part where what looks like a vacuum valve is.

Avanti,

If fuel is not flowing through the WUR, you have a clogged WUR. PM sent.

Tony

[boyt911sc]

Originally Posted by boyt911sc

Avanti,

If fuel is not flowing through the WUR, you have a clogged WUR. PM sent.

Tony

Paul,

I shipped the package with your WUR-033 today. The test shows the WUR is clogged and no fuel passing through it. Same control fuel pressure of 70 psi. recorded. The engine will have a difficult time to get it running and I doubt it would even start (?). It would start and run very briefly because of the fuel coming from the CSV after several failed attempts. From our long telephone conversation, you seemed to be a very capable troubleshooter. Keep us posted.


Tony