911 sc cis residual pressure
 

Good day to All!

Working on my best mans car. 1981 SC EURO no lambda.

Having cold start issue. Will fire after 10-15 sec cranking.

1. WUR 089 cold / warm / residual pressures within spec.
2. New pump / check valve / genuine accumulator (3 port) and FD pressure relief valve
3. New cold start valve. Tested for voltage supply when cranking. All good. This also confirms thermotime switch working properly.
4. New injectors
5. Smoke tested. No leaks detected
6. Thermo valve working. No vacuum at cold start. Will open about 5-10 sec later. Ambient temp during test 20 celcius

The problem is when first crank in the morning she will fire but will not start. It seems that cold start valve is doing its job but no sufficient fuel to keep it running. After prolonged cranking she will fire, will hunt a little and all normal afterwards. Steady idle at 1200 rpm, reducing to 1000 and settles to steady 900.

All the above leads me to conclude that she is starving for fuel, so i let the engine cool down over night and next morning i cracked open the WUR inlet hose from the FD. NOTHING! Not even a drop of gasoline. I then removed the FD relief valve. Only a couple of drops.

FACTS: Eventually after some hours the residual pressure is 0 bar.

MY QUESTION is. After 24 hours of stand still the lines are supposed to be empty???

Can someone please do this test and revert with feedback or share his knoledge?

Thanks
George

I recently changed my accumulator to a later (larger 80ml) unit and when pulling the old one out I had plenty of fuel come out of ALL of the hoses

ps: will be posting the original accumulator in classified soon

Thanks for the info.

Just to confirm. Was this fuel spill after long rest period? Lets say overnight?

residual pressure usually effects hot start the most.

you really need gauges to check RP.
something to ponder. if there is no RP, then where is the CSV getting fuel pressure from to fire.

hunting = too rich.

you can remove the connector on the top rear of the AFM. this will run the FP with engine off.
when cold, turn key to on for 2-3 sec then start.
if all is well then it is probably RP issue.
start with the check valve.

No issues with hot start. Just to clarify, hot start is considered the period where engine is still hot above 45c where thermotime switch will not activate the CSV.

With the above conditions engine will start flawlessly.

Checked RP. Will keep 1.3 bar for more than 1 hour.

Hunting=rich OR also means that FD is empty of fuel and tries to balance control pressure thus hunting rpm due to unstable pressure?

Morning time i push the FD flap by hand and there is no resistance at all. Is this normal for 24 hour interval or should some resistance be present?

I jumper the pump relay and let the ignition ON for a couple of sec. Flap has resistance and i can hear injectors spray.

Still result is the same.

The Cold and warm pressures are within spec but on the rich side. More specific
Ambient 21c
Cold pressure 1.8 bar
Warm 2.8 bar
With vacuum connected and engine working 3.6 bar
See below graph.


http://forums.pelicanparts.com/uploa...1652881419.jpg

Last but not least i have to mention that after sitting for about 10 hours yesterday, it wouldn't start, but once i disconnected the ground wire from thermotime switch it fired immediately.

Over rich condition?

i am not new to CIS but this is a new challenge.

Shall i increase the cold pressure to upper limit and test? 2 bar instead of 1.8 @ 21c
Will this make any significant impact according to your experience?

Will also test components individually.
Accumulator disconnect, plug fuel return line and check for leaks at bottom port
Have a new FP check valve somewhere. Will replace also

Something i forget?

For reference i also checked ignition timing. My pulley has only total advance notch 25 degrees. Adjusted with vacuum line disconnected. Idle seems to be about 7-10 degrees.

NO
dont change anything until you have done more tests.

pull the connector on the back and run the pump then start it.

hot starts are usually an issue about 20-30 min after shutting down.

you can check CCP after sitting to see how quickly the pressure rises if you are concerned about the WUR being empty.

how are the plugs cap and rotor.

you can also pull down on the sensor plate when cold and hunting to "lean it out" as a test

have you messed with the mixture


dont over think it.

Thanks for pulling the brakes on my thoughts.

Will follow your advise and do these tests.

Rotor and cap good condition.

CO adjusted to 2.5 % idle.

No warm start problem based on your statement (20-30 minutes after shut down)
Engine will start first crank after 2-3 hours.

What is your system my pressure? If that is spec it’s hard to imagine the FD being short of fuel volume.

Did you check the AAR for full open at cold start? Typically that would raise your initially rpm to 1600+ rpm by adding air. You mention your cold start only goes to 1200. AFR is very rich at startup so the added air seemingly helps smooth it out.

Good day

System pressure 5.1 bar

1200 rpm was when ambient temp was 30celcius.
Last night there was a storm and today temp was 18 Celsius. Cold idle 1600 rpm.

AAR was adjusted (altering pin position) a while ago.

Please reply to the following question guys as it is the first time i notice this.

The 089 WUR cold pressure is set by applying vacuum???

For so long time i have been adjusting cold pressure without vacuum and had no problems. See below diagram.

http://forums.pelicanparts.com/uploa...1652958834.jpg

CIS Control Fuel Pressures...........
 

Control fuel pressure is measured as:

• Cold control pressure.
• Warm control pressure.

The above tests could be measured with or without vacuum applied (16” Hg). Without running the motor, you need a vacuum tool to measure the CONTROL FUEL PRESSURE under vacuum.

Tony

Notice the different pressures below the graph. The diff with vs without vacuum is around .7 bar. So you can construct the same CCP graph, roughly, w/o vacuum by moving everything by that amount. Much better to just use vacuum.

Thank you all for the input.

Welcome Tony!

Alright then. Let me adjust the cold pressure by use of vacuum gauge and see what happens.

Will first apply vacuum to my current cold setting (1.8 bar @21c) to see how off spec my WUR is.

Reverting...

Mr SkiVT, sorry i dont know your name. I am George

Based on your observation +0.7 bar my cold control pressure with vacuum should be 1.8+0.7=2.5 bar. Way out of spec to the lean side. Let me check.


Thanks

Yes you are on the right track. Remember your TTV holds off vacuum for 30-45 seconds at cold start so in real world, you were starting your engine at 1.8bar. Still theoretically lean but maybe not as bad as the 2.5bar math you state.

Mike

In order to present facts here is a video of cold start after 9 hours car was parked.

https://youtu.be/oddh3p_FES8

When i disconnect ground wire from tts engine will start.

It leads me to over rich condition with tts connected. But the fact is that wur cold pressure is set to lean.

Tomorrow morning with engine stone cold i will adjust cold pressure under vacuum.

Reverting with photos and video.

Good day

Job done.

Cold pressure with vacuum was 2.3 bar @ 20c ambient.
Adjusted to 1.8 bar. Engine sounds more happy. Picked also 100 rpm more at cold start.

Will let it cool down and give it a try.http://forums.pelicanparts.com/uploa...1653035890.jpg
http://forums.pelicanparts.com/uploa...1653035890.jpg
http://forums.pelicanparts.com/uploa...1653035890.jpg
http://forums.pelicanparts.com/uploa...1653035890.jpg

I like the custom wur adjustment tools :-)

Good day!

After setting the cold start pressure i went out of town for a job.

Car stayed stopped for 3 days.

Started with first crank and all went smoothly.

The main problem has not been resolved though. After 9 hours stopped the engine will not start unless i disconnect the ground cable from TTS, thus disabling CSV.

Although TTS has been thoroughly tested i will change with a known good working unit from my car. I dont really think this is the problem though. After 9 hours the engine temp is about 23 c so CSV should be activated.

Any thoughts on how to proceed?

George,

you wrote, that you were new to CIS...did you already made/checked the basic setting of your CIS? The pressures seems ok to me. Don't be so concerned about the cold pressure of the WUR. Porsche claimed it to be in an interval as shown in the diagram...
When the CSV is spraying gas while cranking and the engine won't start (guess mixture is way too rich) and it will start wihtout CSV, then I guess there could be two problems:
1. too less air
2. too rich mixture in general

You wrote that you already checked the AAR if it opens up while engine is cold and getting closed by heating up? Is it opened up when engine is cold? You should check if the AAR is moving the cover? If it's moving, then probably the whole CIS is misconfigured. Remember: You can manipulate a CIS in that way to correct out / cover faulty parts and you never get an idea that sth could be wrong...

I have a popup valve in my CIS airbox, so I can see if the CSV is spraing gas. Did you checked that in person on your car? Will say - did you saw the CSV is sparing only while cranking?

If all those things are fine, then sth else is still wrong we still don't know unfortunately. In those cases I tend to make a basic setting of the CIS as Porsche recommends:
1. check meticulous the correct height of the sensor plate like Porsche says, to do this correct the spring or the screw underneath depending what your car has
2. turn the CO screw fully close (lean it complete out), then switch on fuel pump (ignition on, remove plug from the sensor plate housing), and start turning the screw cw to "richen" the mixture until you can hear the injectors spraying (squeaking noise), then turn it half turn back, done. (be aware that the injectors are flooding the cylindersif you're too slow!!). Plug back in, ignition off.
3. Turn the idle screw completely in so that's fully closed, then turn it out 2 fully rotations.

Now you're done. Then - if everything works as designed - the engine should start right away on the very first crank. Check idle of the engine (esp. when warmed up), then check the CO setting right away.

The height of the sensor plate impacts heavily the mixture over the whole speed range, and you can balance it out with idle and CO screw so that the normal driver won't recognize it until he requires full power or wondering why the mpg decreases that much...
If this basic setting won't ever work, then you still got another problem to figure out, most likely false air / vacuum leak, which is the hardest enemy on the CIS...

Oh, one addition: Concering the residual pressure and the fuel accumulator....
I had a fuel accumulator which was in spec as the Porsche specs given. BUT: It wasn't as good as it should be. The residual pressure is only one side of the medal! The whole world thinks the fuel accumulator is only for the hot starts. But it isn't.
Together with the check valve it assures that the whole fuel system is fully loaded with fuel, not only for hot start (here the fuel accumulator assures that the fuel remains on pressure to prevent bubbles), but it also assures a proper cold start by assuring the whole CIS system is filled with gas/fuel (otherwise the fuel pump has to refill and repressurize the system while cranking), and it suppresses any pressure pulsations while the engine is running, especially when you're pushing the accelarator quickly, then the suddenly increased amount of fuel is filled for the very first moment from the fuel accumulator, and then afterwards it will be loaded up again by the fuel pump. Also when going on idle it cushes any pulsations given by a dropping sensor plate. So conclusion: The fuel accumulator is important on every operation condition for a smooth and powerrful CIS engine!!It's all about the pressures on a CIS engine....

After replacing the old fuel accumulator I could see, that the residual pressure was far more than 2bar/30psi, and it took much much longer to drop the fuel pressure (now several hours instead only half an hour before as the specs says!!!). Now it takes the whole night to drop completely the residual pressure!!

And the thing is - a very good working fuel accumulator can cover a leaky / faulty check valve close the fuel pump and vice versa a very good check valve can cover/hide a faulty fuel accumulator...

HTH.

Thomas

Dear Thomas
Good day

I am not new to CIS. I own a 911 sc 1982 for 5 years now. i am an automotive engineer in profession. I am not a CIS expert, as mine and my best man's cars are the only CIS cars i have worked with. This is the magic in our profession though. You always learn something new every day.

1. AAR works flawlessly. Will start 1500 rpm and will fully close (confirmed) after about 8 minutes depending on weather condition. Idle set to rock solid 900 rpm after warm up.

2. Will check sensor plate alignment
3. Smoke tested intake. No leaks whatsoever. Planning to do a compressed air test (0.2 bar Max) and spray soapy water. For me this is better method.
4. CO was adjusted to 2.5 % idle. Will reconfirm after sensor plate alignment check. Question regarding this. At 3000 rpm (just revving the engine) the CO% is 0.6% (about 14.2 AFR). Is this normal or indicates unmetered air? The car is Row (no lambda)
5. No pop up valve installed on this air box.

Dear George,

ok, then you're way more experienced in cars than myself...I play around "professionally" with computer software ;-) I own my SC (with lambda) since 2015...before that I wrenched rundimentary on cars, the basic things. The SC is my first historical vehicle, I bought as a basically running vehicle, it was more a project car...and therefore I learned a lot about CIS over the years. I researched a lot on the net with others here in Germany. Unfortunately most of the Bosch services and Porsche dealerships here in Germany are not familiar with CIS cars, when you mention "it's a US spec car" they raise the white flag...so I had to introduce myself into CIS...this is my experience...always following the specs given by Bosch&Porsche...

To the points:
1. Good to know. 8mins is a bit too long for my taste, but I guess this is also factory setup, so it should be ok.

2. The sensor plate alignment is *the* most underrated setting on all CIS cars. It affects the mixture over all speed range far more than anything else!! This is basically the most underrated and unnoticed setting on CIS cars. Here's a video from Klassik ATS / Kurt ands his superb series of Porsche 911 CIS videos, Here he explains as well how to make the sensor plate height setting and the CO setting afterwards (different method wihtout flooding the cylinders): https://www.youtube.com/watch?v=K-OvjlkrgNo&t=2523s
But the whole video series is worth a look: https://www.youtube.com/channel/UCbo48hJkHDikGut5DoL6-sQ/search?query=cis%20porsche%20

3. Do get me wrong - you have to test all the CIS for vacuum leaks, including the brake booster...I purchased a smoke generator (https://shop.autooltech.com/product/pipeline-evap-leakage-detector-sdt106/, it has a tiny air pump and it pumps the smoke into the whole examined system, this in my point of view the only secure way to examine a CIS for vacuum leaks!). Brake Cleaner, soapy water etc. are not that effective! (e.g. https://www.youtube.com/watch?v=QNdQ04halLM)

4. I do not have any experience on a Row 911 SC, but the mixture on a CIS in general should be basically the same as on a US SC with lambda control. 3000rpms is basically cruising on less than 1/3 throttle. Here an AFR of 14-14,7 is ok. When you push the trottle more than 1/3 up to WOT the mixture should close to AFR 12,5. Not much deeper, and even not higher (because then the mixture is too lean and the temps are getting higher and higher which is not good for any reasons. It use the signal from the O2 sensor (currently narrow band sensor, but I used to use a broadband Innovate LC-2 as well). The US SC has a switch on the throttle, this allows the ECU to separate 4 different operation modes (idle, cruising (Lambda contron active), acceleration and WOT, both without lambda control, the ECU then nails the duty cycle on the cycle valve close to 70% to enrichen the mixture for power and temperature management in the engine).
On your car this is alll "coded" in the charasteristics of your fuel distributor, the WUR, and all other parts of your CIS. I guess, in that case the correct basic setting of your sensor plate, CO and idle is far more important than on a Lambda CIS car. Here the electronics will correct any wrong values...

5. Of course the pop up in my car was not intended first and foremost to check the CSV. It orevents exploding the air box. And I had several situations during my diagnosis and experiments on CIS where I could pretty good hearing it working...I definitely recommend to install it on your car as well! It will save you a lot of money and headaches when you have to replace a blown air box...
Depending on the mixture (especially when it's too lean) the engine will back fire into the intake manifoilds and the air box. The bad thing on this - the pressure will then shut the sensor plate into their resting position and the pressure cannot go away that fast. Conclusion: The weakest part will give up and let the pressure go out. Mostly this is the air box...

Don't forget - it's all about pressures on a CIS car. Beginning with the fuel pump which should produce 5-6bars pressure (87psi), a working and sealing check valve behind the fuel pump, the fuel accumulator, WUR, the fuel distributor and not to forget - the injectors...if only one part of this daisy chain won't work properly, it will compromise the whole system...

A CIS fuel pressure gauge is also very helpful on diagnosing problems...this is mine: https://kurth-classics-autoparts.de/gb/warm-up-regulator-wur/227-k-jetronic-pressure-testing-gauge.html

Regards, Thomas

Thomas & Leonardo,

Do you know if your CIS airboxes have the “spider plumbing” for the CSV? The early SC’s did NOT have them but the new replacement CIS airboxes now come with the distribution tubes. Thanks.

Tony

Hi Tony,

mine has the spider plumbing on the old air box when I purchased the car and in the meantime the airbox has been replaced with the same one, also with the spider plumbing. The reason for the spider plumbing is exactly to prevent back firing during (cold) start: The fuel from the csv flows better through the the intake pipes to every single cylinder. So - it's not urgenty necessary fort the engine to run, but it makes the start of the engine much safer...

I don't know if the factory equipped SC's already had the spider plumbing, if I'm right it came with the SCs sooner or later...

Thomas

Hi George

The one chart I have with idle AFR shows model yr 78-80 at 2 - 4%, for 81-83 its 1.0 - 2.0%. The US models recommended settings are different (Lambda control). I have mine 83 ROW set closer to 1.2% or roughly 14.0afr at idle l. At light cruise, afr tends to drift up to around 14.5 and then drops quickly under hard acceleration as vacuum drops. At WOT I end up in the high 12's to 13.0AFR. I am not sure if you need to be under load versus just revving the engine to see this drop at similar RPM points. However, you should see a drop under acceleration as vacuum loss controls enrichment on these ROW models.

Mike

Yes spider plumping type.

Thomas thank you for your thorough reply.

Will check sensor plate allignment. Thanks for the tutorial links also.

Something causes an over rich condition for sure and the only suspect is the fuel distributor since csv gives a very specific amount of fuel.

Maybe the sensor plate is misaligned and the plunger position allows more fuel amount than required.

Will also connect my fuel pressure gauge and check control pressure during cranking at that time.

Any other suggestions are welcomed

Tony what you think about the 0.6 CO% @ 3000 rpm when just revving the engine?

Hi Mike!

Yes 80-83 euro cars follow the 78 model specs since no lambda onboard. So its 2-4% CO at idle. if i am not wrong US 80-83 have retard ignition timing at idle thus the lower emmisions. Can tune it below 2% and see if this helps. I just dont want the engine to overheat.

Thanks for your input. Good to know your Row was close to stoic when crusing. During acceleration the 089 wur will richen the mixture since vaccum starts to apply at the top port which is connected above the throttle body. Lower port will also lose vacuum.

So it looks like the engine is well tuned and also sounds and pulls healthy but still will not start at that specific time. 9 hours after stop unless the csv is disabled.

Tomorrow morning will start like nothing happened.

Fuel Distributor Test.........
 

Leonardo,

Have you tested the fuel distributor? Could you test and confirm that none of the 6 ports is delivering fuel with just the fuel pump running (motor off)? Thanks.

Tony

No i haven't.

How to do this? Slack the lines from the injectors or FD while pump is running?

Thanks

Test Procedure.......
 

Leonardo,

Do you know how to test run the FP without running the motor? A good FD should not deliver fuel to any fuel injector or line when the FP is running (FD plunger @ REST). Pull out all six (6) injectors from the intake runners and place them in suitable container (just in case it leaks). Or simply placed injectors #1, #2, & #3 in one container for the test and do the same to #4, #5, & #6.

Removed the FP relay located in the trunk and bridge terminal 87A & 30 using a suitable jumper wire with in-line fuse. Turn the ignition switch to RUN (not START) long enough to look at the fuel injectors for observation. A few drips is OK but no significant amount of fuel in the container/s. Keep us posted.

Tony

Ok understood. Like doing the injector flow balance test.

I don’t expect any fuel to come out from your fuel injectors. But to play safe, a suitable container is used. I am still trying to understand why disconnecting the CSV in the system makes the motor START. Something strange is happening that we are not aware. Thanks.

Tony

In this german channel they did exactly this test as well on a 924 turbo...there you can see, that injector #4 is leaking while fuel pump is on and FD is not touched...

https://youtu.be/GyOiCBpyCfc?t=886

Before they made the bottle test / injector flow balance test. It turned out that the injectors were still good, but Port #4 of the FD was bad due to a broken diaphragm within the FD...you can see it at the end of the video...

Thomas

Leads me to a rich starting condition under the specific engine state.
Have started many engines with leaking injectors in the past (not CIS). Black smoke and erratic idle BUT engine always starts!

I will also connect my ignition timing strobe and crank the engine at that time. Just in case...
Highly unlikely though

Let me do the tests that we already discussed and will keep you updated.

Appreciate your assistance guys.

Thomas

the German guy on the video is really excited about his findings!

LOL

I am not saying AFR is your issue, just passing along a chart, which shows a different mix spec than the 78-80 SC's. It is not always easy to find ROW specific information.

http://forums.pelicanparts.com/uploa...1653472025.jpg

Yeah, Marco began as a car mechanic and later he became an auto trader. Then he focused on older cars. He fell in love with 5cyl. Audis, began tuning them and ended up to 1/4 mile racing. That's why his nick name "5cyl Marco". Afterwards he built an Audi 80 type B2/type 81 with a tuned 1,8t 20V 4cyl. Turbo engine and others. Now he's trading historical vehicles from the 60 up to 90s, in his channel he's showing the projects. He focuses on low budget cars to buy them at a low price and freshing them up, bringing them back to road of possible (some not) and selling them. For the last three years he started a video series called "Prüfstandstag" (dyno day, every friday in his workshop called "Halle 77" located in Dortmund) dynoing customer cars and showing them in the videos. The series is pretty successful and his community is growing more and more. Very earth grounded and sympathic guy. I like him.

The thing is - he hated the CIS system before, he admitted not to fully understand the CIS system. Now over the last years he's getting more and more knowledge of the system especially while dynoing all kind of these cars as well, like 80s Mercedes, Audis, BMWs and others. So it turned out that the CIS Audis almost all never had their specified hp, only a few cars reached almost the hp they should have. But some other CIS cars (no Audis) did reach their hp. He blamed the CIS system earlier, but now he's getting more and more control over it and he's changing his minds on the system. Several people shared their knowledge as well with him, this boosts him as well. He owns beside the 924 turbo also a ROW 911 SC from '79. He loves the design, but he's not really confident how the car rides. I hope he's gonna take care on it later and not sell it, because it ties up a lot of money.
Conclusion is for me as well more and more for Marco: The CIS is far better than it's image on street cars, not for racing cars indeed. The cars lacking on so much issues. That's also my message - if there's problem on a CIS car - you can fiddle a faulty CIS car to a "good" ruuning car again, but then it still suffers on the previous problems, but those have been hidden. The real problem is still not solved!

A bad cold start might not be an issue in Florida or Arizona, and top end performance is also mostly not a real problem unless you go with the car on a race track ... and fuel economy is also for some Porsche onwers not really an issue. But here in Germany we currently pay for a gallon gas more than 2€ per liter, which is more than 7$ per gallon (premium gas 98ROZ / 93+ MOZ USA)....so basically double the price than in the US, therefore we care about on mpg and performance... call it as a need for efficiency...

Did you already got the workshop manuals from Porsche? They're avaialable on the net...

I recommend the two following books for every SC owner:
1. HAYNES Repair manual Porsche 911 SC
2. Bentley Service Manual Porsche 911 SC , unfortunately pretty expensive

Both do not really cover the CIS and how to adjust it, this makes Kurt from Kassik ATS far more better, but especially on the first one you get far better exploded drawings from every aspect of the car and it lists all the variants of the cars. The second is also very detailed and more to read, and it covers more the details of CIS, but as the first one it also focuses on the US cars and nnot the ROW cars unfortunately.

Thomas

You asked for the the adjustment values for the ("Europa") ROW '81 SC no catalyst, no lambda control:

https://i.imgur.com/Ex8HJNp.png

https://i.imgur.com/zWPIGO6.png

* means disconnected air pump
*** the lower value is desired

The US/California/CAN/Japan Cars were afaik equipped with a catalyst and lambda control, seeable at the lower CO values.
You have to take care about the ignition timing as well, becasuse the ROW model in Germany was specified to run with premium gas (98ROZ/88MOZ/93AON):

https://i.imgur.com/DzKUnls.png

Regards, Thomas

http://forums.pelicanparts.com/uploa...1653477530.jpg
http://forums.pelicanparts.com/uploa...1653477530.jpg


The highlighted in red is the car i am working on. 1981 Row. 930/10 engine
Cold / warm and system pressures are set as per spec.

The total ignition timing mark is at 25 degrees BTDC with vacuum disconnected.

I see that 1-2 CO% is the idle spec. I am at 2.5 % now. DO you know what the *** stand for?

There should be a foot note somewhere.

Thanks