911 sc cis residual pressure

[leonardo911sc]

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.

[Schulisco]

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

[boyt911sc]

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

[Schulisco]

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

[SkiVT]

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

[leonardo911sc]

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

[leonardo911sc]

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

[leonardo911sc]

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.

[boyt911sc]

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

[leonardo911sc]

No i haven't.

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

Thanks

[boyt911sc]

Originally Posted by leonardo911sc

No i haven't.

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

Thanks

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

[leonardo911sc]

Ok understood. Like doing the injector flow balance test.

[boyt911sc]

Originally Posted by leonardo911sc

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

[Schulisco]

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

[leonardo911sc]

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.

[leonardo911sc]

Thomas

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

LOL

[SkiVT]

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.

[Schulisco]

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

[Schulisco]

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





* 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):



Regards, Thomas

[leonardo911sc]

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