CIS Sensor Plate Height

[Schulisco]

No bending of the lever!!!
Your '75 911 might have a "spring" for the lever to rest on when engine is off. You must bent this spring only to correct or adjust the resting position of the lever.

See the K-Jetronic Workshop Manual p.13:



Later models of the 911 has a screw instead which is easier to adjust and lock.

Get the workshop manual by yourself and have a look inside:
http://members.rennlist.org/vilhuer/K%20Jetronic%20Workshop%20Manual.pdf

Entirely introduction into CIS from Bosch itself: https://files.bmwclassic.nl/E21/K-Jet/Bosch_K-Jetronic_web.pdf

The issue I was trying to understand was the 'bucking' at low revs, other than that it starts well idles at 900 and accelerates cleanly to the top of the red line.

Check the fuel accumulator! Even if it holds the pressure as it should it might be the culprit. Why? The FA works all the time when engine runs. The manuals say it silences the vibrations coming from the fuel pump. This is only half the truth in my opinion. It equals the the changing requirements of fuel when the sensor plate lever is moving up and down. This causes quick variations in the fuel required by the engine which cannot be delivered that fast from the fuel tank by the pump over those fuel lines from front to back. To fulfill this need it's urgently required that the FA can move over the full range of moving space smootlhly without hesitations. Mine was tight indeed, but couldn't move freely any more. I checked it by pressurizing it with air (output(s) closed) and suddenly depressurized it by simply opening the hose under pressure (4-5bars / 50-75psi). The spring must immediately relax without any delay! Mostly in those cases of bucking cars it doesn't because of wear/corrosion on the diaphragm or the housing. Then it's pretty clear that the delivered amount of fuel is not correct as required in that moment. Voilà: Car is bucking on low revs.
After replacing the FA mostly you need to readjust the mixture and CO setting. Before that check the sensor plate height and urgently the "injection begin" as I described yesterday. Good luck! Keep us posted whether you succeeded.

Thomas

[booyah911]

Just want to say I'm really enjoying this thread. I bought an '82 SC last year and I'm going through the CIS system now. Rebuilt the WUR after testing pressures, confirmed the aux air slide functions, verified FD and injectors operate properly, and performed a smoke test. Now pulling entire CIS to replace faulty throttle position switch, rubber bits, and address air leaks. These discussions are super helpful!

[E Sully]

Originally Posted by mikedsilva

Cig paper.. ok.. that is very thin.. maybe a couple of thou?

My other question relates to the movement of the plate. Lifting it is resistance free, till the halfway mark (approx)... after that, there is some resistance that feels like it is pushing against pressure. The assembly is out of the car, on the bench, and disconnected from fuel / pumps etc, when I do this.

Is this normal? Or should the plate move freely up and down for the entire movement?
Mike

It should move freely the whole length of travel. If you want to go the extra yard, I did not find it too difficult to clean and lube the air flow meter. It can be a little grungy in there. This was an old one I bought as a spare, it had been sitting a long time in someones garage.



I removed the counterweight, 2 C clips, rubber seals, 1 spring, and 2 ball bearings. The ball bearing were stuck in the old grease, so I used a rare earth magnet to get them out. To remove the shaft, I used a wide screwdriver to gently pry the counterweight screw pinch point on the arm and gently nudged it out with a bamboo chop stick that was handy. It might take a light tap to get it moving, but slides easily once moving.
After that I cleaned and polished everything.


Assembly is not difficult. Lube it with silicone (dialectric) grease. Push the pin in, keeping the small inner arm holes lined up with the large air plate arm. Install a ball bearing, rubber seal, cover plate, and C clip on one side. Then on the other it's similar, ball bearing, spring, rubber seal, cover plate, and C ring. It may be a little tricky since the spring wants to push out the small cove plate, but not too bad. In case you lose track, the spring goes on the side with the slightly thicker boss, left side in the first picture.
It's pretty easy to get the plate centered left to right, and then gently tighten the counterweight screw to lock it in place. Fine tuning center has already been shown in earlier posts.

Here is my 002, one of the earliest CIS.

[Schulisco]

Originally Posted by psychoideas

https://jimsbasementworkshop.com/CIS/pages/comp_page.html

FYI
Now available again under new URL:

https://cis911primer.com/home.html

@booyah911
Pleased to hear.

You all already know KlassikATS Youtube Channel, was mentioned on page #1 of this thread. Highly recommended.

Especially the video where he describes the basic adjustment of the CIS and sensor plate height, it slightly differs only from what Porsche and Bosch recommended on the basic setup - he opens one fuel line to a cylinder and awaits fuel coming from the output to determine the "injection begin". Watch it to the end!
https://www.youtube.com/watch?v=K-OvjlkrgNo&list=PLkWFofpgz2OgF9FdliKnlzuY0pygqRkMj&index=4

Thomas

[animal_uk]

I cannot get to the car at the moment to check things and I can see how the sensor plate height can be adjusted but not the angle. I am reluctant to remove the air flow meter again without having a plan.
Because the sensor plate position at the FD end is correct I think that it is probably as good as I can get it. It would be nice though to get the far end at or below the narrowest point like in the picture.
The pictures Ed shows are very helpful to remind what it looked like.
The accumulator may be worn although I renewed it about 70,000 miles or about 15 years ago.

[animal_uk]

Just seen the previous post and will watch the youtube video mentioned.
Good to see that Jim's basement stuff has been rescued .

[Schulisco]

Originally Posted by animal_uk

I cannot get to the car at the moment to check things and I can see how the sensor plate height can be adjusted but not the angle. I am reluctant to remove the air flow meter again without having a plan.
Because the sensor plate position at the FD end is correct I think that it is probably as good as I can get it. It would be nice though to get the far end at or below the narrowest point like in the picture.
The pictures Ed shows are very helpful to remind what it looked like.
The accumulator may be worn although I renewed it about 70,000 miles or about 15 years ago.

The angle of the sensor plate is afaik neglectable if the sensor plate is not manipulated.

The sensor plate height defines the range the lever makes according to the amount of sucked air. This corresponds to the amount of fuel. This is the main parameter to define the mixture besides control pressure and lambda control. But the sensor plate height must always be seen in conjunction with the injection begin as I wrote several times.
A correct sensor plate is worth nothing if the injection begin/base setup of CIS is not adjusted as described in the manuals.

If your FA is that old I would consider it at least as suspicious and I would check it with the compressor test to provoke a quick move to see hesitation if present.

Thomas