High CIS Fuel Pressure

[LCOX]

I'm checking the system, control and residual pressures on my 76 cis 911.

With guage installed I'm getting 88lbs (6 bar) of fuel pressure in the system which looks to be way too high. Shouldn't it be in 64-74lb range?

Any ideas why the fuel pressure is too high and where to start? Thanx L

[E Sully]

One thing to check is the regulating valve is moving freely and the o ring is not damaged. Pressure is adjusted by adding and removing shims from under the spring.
Another problem could be from restrictions in the return line to the gas tank.

[T77911S]

first, make sure you are doing it right. when ever i find something that is this far out of whack, i make sure i did not do the test worng. (do you have the gauges connected correctly).

then check the input screen to the WUR. it gets clogged.

then make sure you dont have a restriction in the return line.

THEN i would pull the regulator out of the FD.

do the easy stuff first.

[boyt911sc]

LCOX,

Assuming that your pressure gauge is not defective and you are getting these high pressure reading/s, these are the most likely culprits you have to check or investigate:
1). Return fuel flow is blocked or restricted.
2). Defective primary relief valve in the FD.

This is how you could locate or identify your problem.
1). Connect the CIS pressure gauge between the WUR and FD. Install it correctly.
2). Locate the main return fuel line fitting behind intake runner #3. Loosen it and disconnect. Secure the end of the fuel line going to the gas tank up high in the engine bay (use a string to secure it). Residual fuel will flow out when you break this connection and be ready to have a piece of rag or a container ready.
3). Connect a temporary plastic hose for the return line from FD to large jar or container to collect the recycled fuel during the test. Secure both line and container.
4). Now, you are ready for the test:
4-a. Inspect everything and test run the FP. Follow the conventional procedure for doing FP test using terminals #87a and #30 with the ignition switch @ ON position (not start).
4-b). Measure your control and system fuel pressures. Record the readings.

Doing the above procedures will isolate where the blockage or problem is located. Keep us posted.

Tony

[E Sully]

System pressure is not affected by a clogged wur screen, that is a control pressure issue.

[T77911S]

yea, your right, i was thinking control.

[LCOX]

Ed I took the little regulating valve out of the fuel distributor and it moved freely with no binding. The small oring on the end is good as well

There were 3 shims behind the spring. I took 2 of them out ran a fuel pressure test again and the fuel pressure dropped 5 lbs down to 83 lbs.

Tony. I also followed your advice and disconnected the return line union back at cylinder#3 and ran the fuel pump. The fuel flowed freely from the engine side of the union with good pressure filling up a small empty water bottle in a short time. What next?

[LCOX]

My apologies Tony. I will need to reinstall the pressure guage again and check cold and warm control readings with the return line disconnected.

I'll post these readings as well asap. L

[theiceman]

Originally Posted by LCOX

My apologies Tony. I will need to reinstall the pressure guage again and check cold and warm control readings with the return line disconnected.

I'll post these readings as well asap. L

Maybe you miss-spoke but it is system pressure readings you are checking right?

Not control pressure.

[boyt911sc]

Originally Posted by LCOX

My apologies Tony. I will need to reinstall the pressure guage again and check cold and warm control readings with the return line disconnected.

I'll post these readings as well asap. L

LCOX,

Connect the pressure gauge and run the FP. Measure the fuel pressures (cold control and system). No need for the WCP (warm control pressure) for this investigation. We are trying to determine where the problem could be occurring at. So knowing the fuel pressures with the return line disconnected will direct us where to investigate next. Keep us posted.

Tony

[cole930]

LCOX:

I just went through a similar issue with my 930. I removed and blew out every single line in the fuel system. I sent the fuel distributor out Larry at flow tech to test. I ran fuel tests and put the return and fuel lines in a glass jar and ran the fuel pumps.
I pulled my hair out for 3 weeks trying to find the issue. When I pulled the return line off at the tank, for the third time, I immediately plugged the outlet at the tank to keep the fuel from running out while I checked the flow in the return line to the tank again. In doing so I bumped the plug I had put in the return line fitting at the tank and it fell out, the fuel started running out of the return line fitting onto the floor at the tank and then suddenly stopped. I knew there was about 1/2 a tank of fuel in the tank so why did it stop flowing.
The fuel return line was plugged inside the tank where the line enters the swirl pot. The fuel I had seen running out of the tank when I pulled the return
line and inserted my plug was simply fuel that was trapped between the clog and the fuel return line fitting on the tank.
I worked for several hours trying to rod out the return line to no avail. I ended up taking the tank to a local radiator shop and they cut a 4" hole in the top of the tank and we were able to rod out the clog from inside the tank after removing the swirl pot.
We reinstalled the swirl pot and welded the piece removed back onto the tank and all is well. I would suggest you pull the return line off at the tank and check for a good fuel flow out of the return line to make sure that is not your issue.

Cole

[theiceman]

Wow Cole that is just nasty .. the Porsche gods were punishing you for some reason ..

ever determine the nature of the clog ? you gotta figure just about anything would disolve in gasoline

[prebordao]

well... gasoline can "make" it's own clogs and they're nasty

I had the same issue and it took a lot of tank cleaning and prodding with a plumbers "snake" to get rid of it.

[LCOX]

Well using Cole's and Tony's advice I think I've found it.

With gauges hooked up and the fuel return hose diconnected at #3 I'm getting good fuel flow with the guage valve on system pressure and also good fuel flow when the valve is open to the warm-up regulator.

Tried to blow through the disconnected fuel hose going back to the tank and could just barely get air flow through to the tank. So I disconnected the return line at the bottom of the tank and gas only dribbled out of the gas tank.

So it looks like I'll be pulling the tank. oh by the way. System pressue with the return fuel line disconnected is 70 lbs and cold control pressure with the line disconnected is 10 lbs. Both times I got really good flow from the dicconnected fuel line basically filling up an empty 16 oz water bottle in about 10 seconds.

[boyt911sc]

Originally Posted by LCOX

Well using Cole's and Tony's advice I think I've found it.

With gauges hooked up and the fuel return hose diconnected at #3 I'm getting good fuel flow with the guage valve on system pressure and also good fuel flow when the valve is open to the warm-up regulator.

Tried to blow through the disconnected fuel hose going back to the tank and could just barely get air flow through to the tank. So I disconnected the return line at the bottom of the tank and gas only dribbled out of the gas tank.

So it looks like I'll be pulling the tank. oh by the way. System pressue with the return fuel line disconnected is 70 lbs and cold control pressure with the line disconnected is 10 lbs. Both times I got really good flow from the dicconnected fuel line basically filling up an empty 16 oz water bottle in about 10 seconds.

LCOX,

It would take less than 30 mins. to determine the location of your problem and you did well. Now, for draining the fuel in the tank, I would suggest that you get sufficient containers if you have more than half tank full. If you could drain the gasoline by letting it drip out, that would be convenient. Otherwise, you might have to siphon the fuel. Stay safe and keep any source of ignition or sparks away from your work area.

Tony

[porwolf]

Great to report a solution to the problem as a finish of the thread. Thank you!

[cole930]

Tony:

I would not pull the tank until I tried roding out the return at the tank. If you
have any fuel at all coming out of the return line there is a chance you can
get it without removing the tank.

Go over to Auto Zone and buy a cheap manual choke cable, about $6.00,
Take it back and try pushing it back and forth into the return line. If you are
not totally clogged there is a good chance you can work the cable back and
forth and get through the clog.

Worth a try before pulling the tank.


Good Luck !!!!

Cole

[boyt911sc]

Originally Posted by cole930

Tony:

I would not pull the tank until I tried roding out the return at the tank. If you
have any fuel at all coming out of the return line there is a chance you can
get it without removing the tank.

Go over to Auto Zone and buy a cheap manual choke cable, about $6.00,
Take it back and try pushing it back and forth into the return line. If you are
not totally clogged there is a good chance you can work the cable back and
forth and get through the clog.

Worth a try before pulling the tank.


Good Luck !!!!

Cole

Cole,

Why would you try to remove the blockage or debris in the fuel tank with gasoline in it? I've done this several times in less than an hour by simply draining the gasoline from the fuel tank by detaching the delivery line, return line, fuel gauge sender unit, and fuel tank filter. You could clean the inside of the fuel tank manually by using different techniques or methods or simply bring it to a radiator shop.

The key to this project is determining where the problem originates. How long did it take you to realize that the blockage or restriction was originating from the tank itself? An hour, a day, or a week? Whatever technique works for someone is good. It is a matter of choice.

Tony

[porwolf]

Originally Posted by cole930

Tony:

I would not pull the tank until I tried roding out the return at the tank. If you
have any fuel at all coming out of the return line there is a chance you can
get it without removing the tank.

Go over to Auto Zone and buy a cheap manual choke cable, about $6.00,
Take it back and try pushing it back and forth into the return line. If you are
not totally clogged there is a good chance you can work the cable back and
forth and get through the clog.

Worth a try before pulling the tank.


Good Luck !!!!

Cole

I agree, it may not be necessary to pull the tank. I also had to clean out my return fitting into my '79SC tank after a 16-year hiatus. It was plugged solid! I used a sing snake from Orchard Supplies hardware store. That was a short, about 18 inches long stiff steel spiral similar to a rotor rooter snake cable. It had a simple wood handle on one end. I probed with that snake into the return tube in and out for about an hour. Though I had the luxury of being able to do it on my mechanic's hoist. After that work the passage was clear. I could easily blow compressed air into the empty tank. Problem solved!

[cole930]

My Bad !!!!!

I figured we were all smart enough not to try roding out a gas tank
without draining it first.

Return line clogs are usually in the 2 90 degree bends just before
entering the swirl pot.






Cole