CIS problem: system pressure = control pressure. Both wrong.

[worn]

Time has passed and I think I see some light in the tunnel. See last page.

I rebuilt my motor that was running before.
1980 911sc
98 mm Mahle cylinders replated
Carrillo pistons
Dougherty DC15 cams
Backdated exhaust with SSI and Dansk muffler
MSD ignition

Runs well for 2-3 seconds and then sputters and stops. Doesn’t run at all with thermo time switch disconnected. Dropped the engine and double checked vacuum and electrical connections.

Hooked up fuel pressure gauges to find that both system and control pressures are around 4 bar. Control way high.

Cleaned up the WUR innards, and was rewarded with system pressure at about 4 bar and control pressure at about 2.2. Engine ran for ten minutes until I turned it off as the garage was getting too smoky - hose came off.

After about an hour I tried again. No start. Then discovered that both control and system pressure matched again - this time at around 2.5 bar. This appears to be a trend because after cleaning out all of the hoses related to the CIS, I now have both system and control pressure matching at three bar. Again the engine starts well and falters,

What would possibly allow system and control pressure to match???

Fuel pump pegged my gauge at 15 bar and seems to have good delivery. Blew air through the return line to the tank. Heard bubbles.

I am going nuts trying to find a scenario in which system and control pressures wander around but always match?! I do not really want carbs, I want the durn thing to run after all the work. I guess the good News is that I can pull the motor in less than two hours, but that kind of practice I can do without.

Help?!!

[2aircooled]

You can try this :

1. Make sure to bleed air out of the pressure tester lines.
2. Check the Vacuum connection at the top of the WUR, there might be a restriction in the hose, or the hose clamp may be too tight (if missing the reducing socket piece).
3. Check the System Pressure Regulator (located on the right side of the Fuel Distributor and be careful with removing the piston).. There could be crud in there, or problems with the o-rings in it.. With it removed, you can also blow air/cleaner from the WUR return line to see if there is any blockage there..
4. You can also test WUR control pressure throughflow by measuring fuel amount from line at the top of the FD going to WUR (typically 160 to 240cc in 60 seconds according to the Probst book.)

Would also be good to post the model number of the WUR (US 1980 SC should be 090) and whether it's K-Lambda or not..
If you can post pictures of the WUR and the vacuum and fuel connections from it to the throttle body and fuel distributor, it would also help with diagnosis.

Hang in there, your problem is definitely solvable...

cheers,
Jeff
81 911SC ROW RHD

[boyt911sc]

Originally Posted by worn

I rebuilt my motor that was running before.
1980 911sc
98 mm Mahle cylinders replated
Carrillo pistons
Dougherty DC15 cams
Backdated exhaust with SSI and Dansk muffler
MSD ignition

Runs well for 2-3 seconds and then sputters and stops. Doesn’t run at all with thermo time switch disconnected. Dropped the engine and double checked vacuum and electrical connections.

Hooked up fuel pressure gauges to find that both system and control pressures are around 4 bar. Control way high.

Cleaned up the WUR innards, and was rewarded with system pressure at about 4 bar and control pressure at about 2.2. Engine ran for ten minutes until I turned it off as the garage was getting too smoky - hose came off.

After about an hour I tried again. No start. Then discovered that both control and system pressure matched again - this time at around 2.5 bar. This appears to be a trend because after cleaning out all of the hoses related to the CIS, I now have both system and control pressure matching at three bar. Again the engine starts well and falters,

What would possibly allow system and control pressure to match???

Fuel pump pegged my gauge at 15 bar and seems to have good delivery. Blew air through the return line to the tank. Heard bubbles.

I am going nuts trying to find a scenario in which system and control pressures wander around but always match?! I do not really want carbs, I want the durn thing to run after all the work. I guess the good News is that I can pull the motor in less than two hours, but that kind of practice I can do without.

Help?!!

Worn,

Are you sure your gauge registered 15 bar? If it did, then your gauge needs some calibration. Why? Simply because a single CIS FP is not capable of producing 15 bar of fuel pressure. Hope you are not using a HF brand CIS gauge.

You are making this CIS troubleshooting too difficult. And with your questionable CIS gauge added to the equation makes it more complicated. In reality, your problem is quite simple. If you want this motor to run with CIS, you will be disappointed and frustrated because you are not doing it the right way. You are working very hard to get this motor to run and I give you high mark for that.

Have it ever occurred in your mind that maybe there is something wrong with your CIS components or tools? Since you are seeking help, I will offer you some CIS troubleshooting assistance for FREE. Let me test and evaluate your components (WUR, FD, AAR, etc.) and return them to you with the test results. Right now you are hoping that both the WUR & FD are good. But you don’t know that as a fact. Even your gauge is a suspect. Good luck.

Tony

[Bucketlist]

If in doubt you should let boyt911sc help you out.

My story: When I bought my car, it seemed to run fairly well but was really rich. When I first hooked up cis gauges my control pressure and system pressure tested the same. I was told it shouldn't run at all, so I must be doing something wrong. As I worked thru the problems I found the screen to the wur clogged, the mixture screw in the fuel distributor screwed all the way in and siezed, and the needle missing from the system pressure regulator. It took a while to find and sort all of these problems and a few parts that I may not have needed. I did learn all about cis .......this is just a hobby, right?

[gomezoneill]

Listen to Tony he's a stand up guy helps tons of people on the forum.

[boyt911sc]

Jeff,

Sorry. I have to disagree with some of your information. We are just discussing some technical information. You maybe correct and I could be wrong. So don’t take it personal. And I learned a lot from people like you.

Originally Posted by 2aircooled

You can try this :

1. Make sure to bleed air out of the pressure tester lines.

#1. No need to bleed air to measure fuel pressures in CIS.

Originally Posted by 2aircooled

You can try this :

2. Check the Vacuum connection at the top of the WUR, there might be a restriction in the hose, or the hose clamp may be too tight (if missing the reducing socket piece).

#2:
The hose connection on top of the WUR you were referring is not a vacuum line. It is a vent hose connected on top of the butterfly valve in the throttle body. The US spec ‘80~’83 SC CIS don’t use vacuum assisted WUR’s for enrichment.

Originally Posted by 2aircooled

You can try this :

3. Check the System Pressure Regulator (located on the right side of the Fuel
Distributor and be careful with removing the piston).. There could be crud in there, or problems with the o-rings in it.. With it removed, you can also blow air/cleaner from the WUR return line to see if there is any blockage there..

#3:
I agree but use the main return line fitting at the rear side of the FD instead.

Originally Posted by 2aircooled

You can try this :

4. You can also test WUR control pressure throughflow by measuring fuel amount from line at the top of the FD going to WUR (typically 160 to 240cc in 60 seconds according to the Probst book.)

#4:
So what will you do with this information? What you need is fuel pressure not flow rate.

Originally Posted by 2aircooled

You can try this :

Would also be good to post the model number of the WUR (US 1980 SC should be 090) and whether it's K-Lambda or not..

No. US spec 1980 SC should have WUR-072 not -090. Where did you get this information?

Originally Posted by 2aircooled

You can try this :

If you can post pictures of the WUR and the vacuum and fuel connections from it to the throttle body and fuel distributor, it would also help with diagnosis.

Hang in there, your problem is definitely solvable...

cheers,
Jeff
81 911SC ROW RHD

I completely agree with this one.

Tony

[worn]

Wow. Thanks to all. I have an alternative gauge I plan to use in order to check the accuracy of the HF gauge. If it were temperature I would use boiling water as a standard. Volume I would use a micro pipetor or maybe a graduated cylinder. My micrometers have length standards that came with them. But pressure is a bit harder, so I will see if two gauges or maybe three gauges match.
Will also double check pump pressure. Then I will get back to you.
The FD number ends in 77, so that is correct. I will get the number off of the WUR. No vacuum line indeed.
Thanks so much!

[2aircooled]

Hi Tony,

Thanks for all your comments, no worries... I have learned a lot from your posts, so its nice to hear from you..
I have been a long time lurker on the forum, and have only recently started posting a bit more after owning my SC for more than 10 years... Plus, posts from you and other CIS gurus on the forum have helped to solve other members CIS issues, hence didn't see the need to add in redundant posts...

I'll reply to the points below, sorry can't figure out how to do the individual quotes like you did, so will just list out below...

#1 Bleeding air, yes I agree with you on this too, as I also don't bleed (air) when I am testing CIS pressures, but based on Worns problems with reading pressures, I thought that it would be a simple, no-cost step to do just in case... (Charles Probst recommends this in his book though, as does the Bentley manual....)

#2 Yes you are completely right too that it is actually a vent line, I used the wrong term to describe it, it is also a vent line on the vacuum assisted 089 WUR in my car.....To explain further., as illogical as it may sound, I actually had a control pressure problem with the WUR vent, what happened was that the reducing socket was lost when I bought the car and the rubber hose was directly connected to the vent on the WUR side, and I stupidly tightened the hose clamp ABOVE the vent outlet, effectively clamping the hose shut and"sealing" the WUR vent.. As the WUR internals are pretty well sealed up, this blocking of the vent caused the vacuum assist diaphragm to somehow increase the vacuum and cause higher than spec control pressures which caused lean AFRs and some slight pinging..(Engine not damaged thankfully....)

#3 Agree with you that undoing on the FD side is the right way to it, but with the engine in the car it's a bit easier to undo at the WUR side, so I do it for convenience...

#4 In Charles Probst book, he suggests doing this test if you are having problems with mixtures that are either too rich or too lean, this test is to check if the control pressure restrictor in the FD is either clogged or eroded... If it is out of spec, he says to replace the FD... The idea behind this test is to avoid replacing a perfectly good WUR without actually solving the problem.

#5 The US CIS has more variations than the ROW, so I might have jumped the gun on saying that it would be an 090, as I am actually not familiar withe US models since we don't have any here where I live.... FYI I got the information from the Porsche 911SC and Turbo Service Information for 81 Model yellow cover booklet, there is a nice page in there that lists the Bosch part numbers for the primary CIS components such as the FD, AFS, AAV, AAR, WUR for all the 1981 ROW and US Models..it lists both the 090 and 072 for 911SC-USA models, so I incorrectly assumed that it would be an 090.. The earlier model yellow booklets (78, 80) do not have the CIS information in them, so I thought that 1981 was "close" enough...

Hope Worn get his issue sorted out soon.


cheers,
Jeff

Originally Posted by boyt911sc

Jeff,

Sorry. I have to disagree with some of your information. We are just discussing some technical information. You maybe correct and I could be wrong. So don’t take it personal. And I learned a lot from people like you.



#1. No need to bleed air to measure fuel pressures in CIS.



#2:
The hose connection on top of the WUR you were referring is not a vacuum line. It is a vent hose connected on top of the butterfly valve in the throttle body. The US spec ‘80~’83 SC CIS don’t use vacuum assisted WUR’s for enrichment.




#3:
I agree but use the main return line fitting at the rear side of the FD instead.



#4:
So what will you do with this information? What you need is fuel pressure not flow rate.



No. US spec 1980 SC should have WUR-072 not -090. Where did you get this information?




I completely agree with this one.

Tony

[worn]

Well, I am back. As I said I pulled the motor to check all fuel and vacuum lines. I also pulled out and quickly replaced the regulator plunger on the FD. All vacuum lines and regulators looked fine. The wires went to the right places. The fuel lines between components were open and clear. The lambda valve had the proper resistance, but beyond that I cannot tell.
WUR: 140072
FD: 0438100007
yesterday I went back with a different pressure gauge, and that confirmed system pressure still about 2.8 bar, and wherever the system pressure went, the control pressure followed.

I put the gauge at the end of the fuel accumulator outlet. That produced 6.2 bar (my earlier number was a mistake in reading the gauge). Opening the valve produced 480 ml/30 seconds. This is less than half that indicated by the Bentley manual. Placing the gauge in line between the fuel accumulator and the filter produced fuel pump pressure varying between 5.7 and 6.2 bar. After pump shut off the fuel pressure fell steadily to 10 psi - much faster than the change in residual pressure measured at the system pressure port on the top of the FD.

Is it time to send you stuff Tony? Fuel pump delivery rate seems low, but the pump seemed to be able to hold pressure when connected and delivering fuel.

[boyt911sc]

Warren,

Since the motor is out, remove the following and shipped them to me.

• Fuel distributor
• Warm up regulator
• Cold start valve
• Fuel injectors
• Etc.

Remove all the fittings for both FD & WUR. Wrap some electrical tape around the FD to keep the plunger from falling out and place it in zip lock bag. There are six (6) micro filters in the FD that might get dislodge during transit. Pack the FD well because it tends to break the shipping box during transit. Make sure you have enough insurance coverage in case the package got lost during transit.

Before you removed the components, I like you to check the following:

• Cold control pressure
• Warm control pressure
• System pressure
• Residual pressure
• Heater resistance (Ohms) for WUR at room temp.

Post these numbers and will compare our data later after I received the package. Also I like to compare the readings of our pressure gauges. Will PM you of my address. Thanks.

Tony

[2aircooled]

Hi Warren,

Your Fuel Delivery rate looks to be below spec and it might be worthwhile to investigate a bit further.
Recommendation from Bosch injection book is to replace fuel filter and blow compressed air through supply line to be sure its open. If still out of spec, fuel pump may not be operating correctly.

You don't have to hook up the gauge to the FA outlet to check fuel delivery, just measure from the return line.

[worn]

Thanks. I was wondering about that too. The gauge was there to test fuel pressure, and it has a valve inline, so I simply opened the valve to measure flow.

[worn]

Tony,
In light of the fuel delivery being a bit less than half of spec, do you think I ought to try another fuel pump? About 8 years ago I was having fuel problems mixed with a bad Permatune ignition box and replaced the fuel pump. I think I have the old one, which may well run as it ought to (I was really chasing my tail then). I could swap and check. My only reason I haven't done that is that while the pump didn't delivery properly into a beaker, when hooked up to the motor, the pump delivered the proper fuel pressure.
Thanks
Warren

[boyt911sc]

Warren,

Repeat the flow rate test. The FP should deliver at least 1 liter per 30 sec. And make sure you have a fully charged battery. Disconnect the main delivery line to the fuel accumulator with the metal curved tube. Stick it to container and test run the FP for 30 sec. Take a couple of trials and compare the measured volumes.

If you get 2 liters per min. or more flow rate capacity, then the FP is still good. Just make sure battery is fully charged when you do this test. Keep us posted.

Tony

[worn]

OK. Things intervened but I finally did more tests. I originally was worried about the fuel pump delivery. After several retests I find that the pump produces 10 bar from the line going to the accumulator. It flows at about 3 liters per minute. My earlier flow rate was through the tube that came with the pressure test kit. The line is pretty small and restrictive.

System pressure varies from day to day between 2.5 and 2.9 bar. Control pressure consistently matches system pressure. In addition, when I stop the fuel pump, residual pressure stays at 2.5 bar for quite a long time. Not like what I consider normal where the pressure drops to about 1.3 bar and stays there for half an hour. Now it stays higher.

Any ideas about what is going on? I am thinking that either flow is being limited in by some restriction, preventing system pressure from rising. Or flow going back to the tank lacks a restriction that should be there, thus bleeding pressure away too easily.

Could the frequency valve lower system pressure if it got stuck open? It vibrates when I turn on the pump, but I am not sure how good a test that is.

[boyt911sc]

Originally Posted by worn

Well, I am back. As I said I pulled the motor to check all fuel and vacuum lines. I also pulled out and quickly replaced the regulator plunger on the FD. All vacuum lines and regulators looked fine. The wires went to the right places. The fuel lines between components were open and clear. The lambda valve had the proper resistance, but beyond that I cannot tell.
WUR: 140072
FD: 0438100007
yesterday I went back with a different pressure gauge, and that confirmed system pressure still about 2.8 bar, and wherever the system pressure went, the control pressure followed.

I put the gauge at the end of the fuel accumulator outlet. That produced 6.2 bar (my earlier number was a mistake in reading the gauge). Opening the valve produced 480 ml/30 seconds. This is less than half that indicated by the Bentley manual. Placing the gauge in line between the fuel accumulator and the filter produced fuel pump pressure varying between 5.7 and 6.2 bar. After pump shut off the fuel pressure fell steadily to 10 psi - much faster than the change in residual pressure measured at the system pressure port on the top of the FD.

Is it time to send you stuff Tony? Fuel pump delivery rate seems low, but the pump seemed to be able to hold pressure when connected and delivering fuel.

Warren,

Please double check the Bosch ID # for your fuel distributor. It should not be -007. Keep us posted.

Tony

[worn]

I note that a Bosch manual says that the fuel flow test point is actually at the outlet from the fuel distributor back to the tank. Did I measure flow wrong again?

[worn]

It is indeed 007. The WUR is also correct for the year.

[boyt911sc]

Originally Posted by worn

It is indeed 007. The WUR is also correct for the year.

Warren,

The WUR-072 is the correct WUR for ‘80 SC US spec. and the correct FD is not -007. Check with the different owners of the same MY car what fuel distributors they have in their cars. Or use a reference manual for the correct CIS components for different MY. Keep us posted.

Tony

[worn]

Sorry. Ends in 077, not 007.