Cold control pressure K-jet

[mhjjvh]

Hi,
I'm from the Netherlands and restoring a Porsche 911 SC Targa 1980 US model, which has been standing still for a few years. I performed big maintenance (engine and transnission out), and now I'm working on the fuel system (engine in te car again).
The engine runs but starts very difficult. I did a fuel pressurte test and found out that my system pressure is OK at 4.5 bar (new fuel pump). My cold control pressure, after opening the test valve, doesn't drop (still 4.5 bar).
I revised the WUR with a kit, so this should be OK now. After a 2nd test the CCP is still the same as the system pressure. What could be wrong here?
Options:
1. WUR still not OK (what could be the problem)
2. return line to fuel tank blocked (old fuel/sludge?)
3. timing/frequency valve/Taktventil not OK
4. ...?

Can anyone at this forum please help me out here?

Thnx!
Maarten

[Schulisco]

You're able to measure control pressure. Very good, as this is one of most important parameter on a CIS...the control pressure is equal to the system pressure which is absolutely not correct, it's way too high. On cold start at 0°C it must be on 1,5bar with test valve at the pressure gauge open. I suppose the WUR (warm up regulator) is bad and needs an overhaul. Mainly the rubber O-ring seals are bad and the internal parts may corrode due to water coming from detoriated (ethanol) fuel. There are supplier for overhauled parts as well as diy overhaul kits.

Here's a diagram showing the CP for your car:
https://forums.pelicanparts.com/porsche-911-technical-forum/1118039-wur-ohm-reading-0-00-a.html#post11691111

After long time sitting you have to inspect visually all parts of the CIS & fuel system of the car as modern fuels with ethanol forces and speeding up corrosion. Incl. the gas tank which supposingly is corroded too and - if so - needs a replacement. Otherwise rust and dirt get into the CIS system anytime again and again. If the return is blocked, then try compressed air to get it back free. The fuel must be able to circulate between engine and tank anytime.
The frequency valve must vibrate when engine is running. Mostly the valve and it's electronic box aren't bad either, but the relay to operate both under the passenger seat is either bad or the wrong type. If that amount of fuel from the cycle valve is missing due to malfunction, many mechanics enrich the mixture by "tuning" the sensor plate height (lowering than original) and the mixture screw. In consequence everything from CIS is out of spec and you have to check everything. (Fuel) Pressures and air tightness means the world on a CIS. For a successful job on a CIS car you need a good basic knowledge of how every part of CIS works and how to shall work together.

Get familiar with CIS by these sources:
https://cis911primer.com/home.html
https://www.youtube.com/playlist?list=PLkWFofpgz2OgF9FdliKnlzuY0pygqRkMj (whole playlist, the 2.7 CIS is mostly the same of the lambda CIS of your car without the lambda part)
https://files.bmwclassic.nl/E21/K-Jet/Bosch_K-Jetronic_web.pdf

As a dutch man are you able to read and understand german?
SSP 44 from VW explains very basic how CIS works:
http://www.volkspage.net/technik/ssp/ssp/SSP_44.PDF

We had plenty of discussion threads here about troubleshooting the CIS on 911's up to 1983. The best is to dive into the literature to gather as much as knowlodge as possible before you continue the troubleshoot on the car. E.g.
https://forums.pelicanparts.com/porsche-911-technical-forum/1119098-911-sc-cis-residual-pressure.html
There are many more. Best is to use the search function here (or Google itself with reference to this forum) to find threads dealing with CIS and it's components.

Thomas

[boyt911sc]

Originally Posted by mhjjvh

Hi,
I'm from the Netherlands and restoring a Porsche 911 SC Targa 1980 US model, which has been standing still for a few years. I performed big maintenance (engine and transnission out), and now I'm working on the fuel system (engine in te car again).
The engine runs but starts very difficult. I did a fuel pressurte test and found out that my system pressure is OK at 4.5 bar (new fuel pump). My cold control pressure, after opening the test valve, doesn't drop (still 4.5 bar).
I revised the WUR with a kit, so this should be OK now. After a 2nd test the CCP is still the same as the system pressure. What could be wrong here?
Options:
1. WUR still not OK (what could be the problem)
2. return line to fuel tank blocked (old fuel/sludge?)
3. timing/frequency valve/Taktventil not OK
4. ...?

Can anyone at this forum please help me out here?

Thnx!
Maarten

Maarten,

For the control pressure to read the same as the system pressure in a CIS:

• The return line or the WUR itself is not flowing thru. Presence of blockage.
• Or you are using a pressure gauge tester with a Schrader valve.

Any of the above will cause the problem you are having. Could you post a picture of the pressure gauge tester? Thanks.

Tony

[mhjjvh]

Thnx Schulisco & boyt911sc for your replies!!

I have been working on this again today. The frequency valve works when the ignition is turned on.
If I loosen the return line on the WUR, the pressure remains 4.5 bar. I then removed the WUR again and opened it to check whether the passage from the FD to the membrane was open. This turned out not to be the case. I sprayed it with carb cleaner from both sides and let it sit for a while. Then sprayed it with air and the passage was open again. I reassembled the WUR agian and mounted it back on the engine. New pressure test and unfortunately still 4.5 bar CCP.
Conclusions:
1. WUR is really not good anymore
2. the return line is clogged

Now I have tried to blow through the return line with the compressor, but of course that does not work well due to the banjo connection. Does anyone have any idea how this could be blown through? Can I pull the banjo connection out of the line and push it back in later without it leaking? This line runs behind the engine and I cannot clearly see where it runs. According to the Bosch schedule it should come out on the FD.

[boyt911sc]

Maarten,

Do this simple test to confirm where the blockage is located. With the fuel pressure gauge connected, disconnect the fuel line to the WUR and test run the FP. The WUR is now isolated and place the end of the disconnected fuel line to a collection vessel.

Read the pressure reading while the FP is running with the valve opened and closed. Post your pressure readings. Thanks.

Tony

[mhjjvh]

Originally Posted by boyt911sc

Maarten,

Do this simple test to confirm where the blockage is located. With the fuel pressure gauge connected, disconnect the fuel line to the WUR and test run the FP. The WUR is now isolated and place the end of the disconnected fuel line to a collection vessel.

Read the pressure reading while the FP is running with the valve opened and closed. Post your pressure readings. Thanks.

Tony

Yes,of course!
But than still it could be a broken WUR or a clogged return line.

[boyt911sc]

Maarten,

Could you post a picture of your pressure gauge tester? Does it have a Schrader valve? Just curious. Thanks.

Tony

[mhjjvh]

This one…https://www.ebay.com/itm/145263346818?norover=1&mkevt=1&mkrid=711-169407-715209-8&mkcid=2&itemid=145263346818&targetid=293946777986&device=c&mktype=pla&googleloc=9065262&poi=&campaignid=20536901515&mkgroupid=153284523317&rlsatarget=pla-293946777986&abcId=&merchantid=5491955838&gad_source=1&gbraid=0AAAAAo9ZJxteGg9aD99qyWVzSEcUiy_Jn&gclid=CjwKCAiAjp-7BhBZEiwAmh9rBZ2-5K8O2_HYeXlAbo3dvA2oaeMoKKxIw6xESfag3N3BEcd5dZ8oHh oC1mUQAvD_BwE

[boyt911sc]

That’s a good CIS pressure tester. Now time to test the control pressure with the WUR removed from the system. The flow restriction or blockage could be inside the WUR or inside the return line going to the back side of the FD. Good luck.

Tony

[mhjjvh]

Disconnected the fuel line from the WUR. Result is 0 bar when tester valve is opened (as expected).
I disconnected the return line WUR - FD @FD and that one is not clogged. So problem seems to be the WUR.
Maybe I should replace this after all.

[Schulisco]

As said - check that filter screen at the WUR. If it's clogged and you're lucky as the only issue...

https://forums.pelicanparts.com/porsche-911-technical-forum/1037708-911-sc-1980-running-bad-after-cis-rebuild-2.html

https://web.archive.org/web/20240227070218/http://b2resource.com/PDFs/wurservicing.pdf

When it's clean then your WUR is bad and needs overhaul.

You're from the netherlands, so basically the fuel is also containing ethanol which attracts water and may detoriate over the years standing still. I always recommend a fuel stabilizer on every fillup esp. on CIS cars because of that to compensate the humidity and water and preventing corrosion in the whole CIS. Most of these cars have an (re-)opened gas tank ventilation so that air may get into the tank to bring in humidity. So urgently have a look inside the fuel tank! It may be corroded due to detoriated fuel. If this is the case, than you have to replace the tank (or clean it but this is often a bad job and mostly not durable) and check all the rest of the CIS for dirt and rust...to check that use an endoscope or remove the fuel sensor on top of the tank. Use a new sealing then back again.

Thomas

[mhjjvh]

Hi Thomas, I already replaced the fuel tank with a brand new one, that was the first thing I did when I started on this car. Also the fuel pump and fuel filter are new ones.
I think I'll send the WUR to a local specialist and also the FD for cleaning and readjusting, just to rule out as much as uncertainties possible.

[Schulisco]

Originally Posted by mhjjvh

Hi Thomas, I already replaced the fuel tank with a brand new one, that was the first thing I did when I started on this car. Also the fuel pump and fuel filter are new ones.
I think I'll send the WUR to a local specialist and also the FD for cleaning and readjusting, just to rule out as much as uncertainties possible.

Ahh, okay. Sounds good and seems to be a reasonable plan. Curious what you'll gonna find out. To take the FD in concern too is imo a very good thing as they suffer also quite much when standing still with fuel. So you rule out two of the most important things. I recommend also to replace the injection valves with new ones and replace - if not happened yet - all rubber seals & hoses / o-rings of the CIS. Saving money on these things is the wrong way. You can try to clean the injection valves. But mostly they wear out mechanically as they're spring loaded valves with a spec'd opening pressure between 2,5-3,4bar pressure which is pretty large interval. Good luck and happy X-Mas!

Thomas

[mhjjvh]

Hi,
Update on my project...
I sent the FD, WUR and Air Flow meter to a specialist for refurbishment. Received them back two weeks ago. Yesterday I found some time to mount all the componentes on the engine again, connected all the fuel lines and bleeded the system.
Next thing was to perform the fuel pressure test again with the following (satisfying) results (and yes, it was cold in my garage):
Pump: 5.0 bar
WUR cold: 1.33 bar @5 degrees C
WUR warm: 3.6 bar (stopped rising after 4 mins)
Pump: 4.95 (test valve closed)
Residual pressure: 1.15 bar (after 10 mins) & 0.0 bar (after 16 mins)

Conclusion, all looks almost perfect!

The residual pressure though dropped too fast and even to 0.0! To my opinion that is not OK. So, apparently the fuel accumulator needs to be replaced too.

I didn't start the engine, just because it's standing on 4 jack stands. I just replaced all disk brakes and overhauled all calipers. Still need to bleed those.

Thnx again for all help provided.
Grtz, Maarten

[Schulisco]

Originally Posted by mhjjvh

Hi,

Residual pressure: 1.15 bar (after 10 mins) & 0.0 bar (after 16 mins)

...

The residual pressure though dropped too fast and even to 0.0! To my opinion that is not OK. So, apparently the fuel accumulator needs to be replaced too.

Good progress. Yes, the residual pressure falls to quick. Falling to zero sometime is normal and okay. But as said - not that quick. It should last at least as Porsche spec'd in the tech spec books: 1,3bar after 10mins and 1,1bar after 20mins. Mostly it's higher and longer if everything is in shape.

Check aside the check valve at the fuel pump, they can also leak and let the fuel pressure drop to quick as the injector valves too. They should have an opening pressure between 2.5 to 3.6bar. They may also being worn over time and can start leaking - if so, you'll also loose residual pressure too quick. To diagnose this pull them out of the engine still connected, let the fuel pump run and seeif they leak. While working there check their spray pattern and amount of delivered fuel (simulating WOT lifted sensor plate for 30secs and compare the delivered fuel amounts against the others, max. allowed difference is 5%). If deviation is bigger replace them too...

Thomas

[mhjjvh]

The injector valves have been tested on a test bench when I had the engine out. They were perfect.
I think I'll buy a new accumulator. Only question is, should this be an original one or will an imitation version also do the job?

[Schulisco]

Originally Posted by mhjjvh

The injector valves have been tested on a test bench when I had the engine out. They were perfect.
I think I'll buy a new accumulator. Only question is, should this be an original one or will an imitation version also do the job?

Imitation version?
I only know the original Bosch versions. They differ from earlier 911 up to 1977, they were smaller, with the SCs they got bigger. Check it too when you get it before mounting in the car for tightness and especially smooth and easy movement of the plunger by compressed air. They may corrode when being stored too long with too much humidity as they can corrode in the car stlitting too long with ethanol "poisened" fuel
I described the testing procedure here several times ... Must seatch a bit.

Thomas

[mhjjvh]

Today I completed my brake refurbishment, including. bleeding. I have a firm brake pedal again.
Put the car back in its wheels again and this was the moment to finally test the engine...

And yes, the first time starting it, it started immediately and then stopped again. The second time again, although it kept running a bit longer and gave a few backfires. The third time it started without backfire and kept running at 1200 rpm and without smoke! After about 3 minutes the idle dropped to about 1000 rpm. with an oil pressure of just over 2 bar. The oil level was then however tightly at max. (gauge on the dash).
I let it run for a while and after 5-6 minutes it started smoking again (white smoke). I checked the oil and there was nothing on the dipstick, while the gauge on the dashboard indicated max.
It seems that it is pumping oil into the engine/crankcase, but it's not flowing back to the oil tank, which causes the engine to fill up with oil. Could it be that there is a blockage somewhere and that it is pushing the excess oil out through the exhaust, causing the white smoke?

I have not loosened the drain plug of the oil tank, so I do not know whether and if so, how much oil is still in the oil tank.

I am now going to look it up in my books again and see if I can find the problem. Are there any forum members who can help me here in the meantime?
Thanks in advance!

[boyt911sc]

Maarten,

Use the dip stick to check your cold oil level. Without the motor running and a cold motor, the oil level could be seen on the dip stick. If you don’t find any oil marking on the stick, the oil level is LOW. Add some oil until you get some oil on the tip of the stick. Once you get the level on the oil stick, you have enough oil to run a cold motor. The final test is with the motor at operating temperature parked and idling on a leveled floor with the oil mark between the minimum & maximum hash markers.

Test your residual pressure. There are several known culprits for this problem.

Tony

[Ian Comerford]

Interesting. A smoking engine isn’t necessarily a problem on a 911, they often do this after not being run for a while. I guess that part of the problem you have is not knowing how much oil is actually in there because it sounds like your oil level gauge isn’t working if it’s pegging at the top and you can’t get a dipstick level until it warms properly, by which time you could have done damage if there isn’t enough oil in there. You will get different opinions on this, but if it was me I would drop the oil from the tank and crank case and, if it’s not fresh, replace it with 10 litres of fresh oil. This will ensure you have enough in there to safely run the engine. If the oil that’s in there is actually fresh, just measure it to ensure it’s around 10 litres and put it back in. Then, to get rid of the white smoke take it for a good drive and use the revs once warm (sometimes called an Italian tune up…). Report back once done and tell us how it performs, sounds, feels etc.