CIS Surging Under Constant load

[kltarga72]

Originally Posted by massmike

Yes, It is most noticeable at light throttle while cruising (Typically 2K-3K rpm). If you accelerate hard the surging is not noticeable. No surging at idle either.

Massmike, I noticed you mentioned when cruising, your in the 2000-3000 rpm range. My experience with my 1980 CIS that if I do run under 2500 rpms I get a similar surging feel. Porsche reccomends 3000-4000 rpms for normal city driving and when cruising at higher speeds 3000-3500 is ok in higher gears
A porsche engineer told me many years ago to keep rpms above 2800 minimum.
Hope this helps

[AndrewCologne]

Originally Posted by pmax

Never heard of the "well known pulling" effect until your link above.

My 80 exhibits no such behavior when "cruising".

That’s because everything is installed correctly and apparently set up properly, so everything runs perfectly.

There are cases where a resulting lambda/AFR value oscillates back and forth with a too high amplitude. Normally, it moves between lambda 1.03 and 0.97, but if it goes beyond, for example, 1.05, you can notice such amplitude oscillations (around 1 Hz) as a “feels like pulling” effect.

Originally Posted by Funracer

.... None of this occurs if the O2 sensor is unplugged. ...

Unplugging the connector and running everything permanently in open-loop mode fixes the symptoms — but not the cause. And those who managed to get everything working again wouldn’t want to give up the regulation anymore.
Fun fact: I don’t know of a single test report from the years 1980–1983 that claimed the reputation of the Porsche and BOSCH engineers was ruined because the U.S. models with the K-Jetronic from those years had issues.

Originally Posted by pmax

My next suggestion ...


Did you connect that yourself ?

You might wanna install the genuine Porsche part.

Yes, connection seems done in a poor way.

Regarding the Porsche part suggestion, ... a genuine BOSCH sensor, or a good-quality alternative from another manufacturer, will work just as well — it simply needs to match the BOSCH part number 0 258 986 501.
However, when using a narrowband sensor, I strongly recommend switching to a 3-wire version with an integrated heater (BOSCH part number 0 258 986 502). Connect the black wire to the lambda connector, and the two white wires from the heater: one goes to ground (GND) and the other to switched 12 V — ideally via a relay controlled by the same signal as the WUR. This way, 12 V is only supplied when the engine is running.

Originally Posted by kltarga72

Massmike, I noticed you mentioned when cruising, your in the 2000-3000 rpm range. My experience with my 1980 CIS that if I do run under 2500 rpms I get a similar surging feel. Porsche reccomends 3000-4000 rpms for normal city driving and when cruising at higher speeds 3000-3500 is ok in higher gears
A porsche engineer told me many years ago to keep rpms above 2800 minimum.
Hope this helps

Nowadays, when society has been stirred up against cars, if you keep driving constantly around the city here in Germany at 3000–4000 rpm, the police will definitely pull you over and remind you that the law requires you to avoid high RPMs.

The rule of thumb is:
When a lambda-controlled K-Jet system is working properly, it delivers performance throughout the entire RPM range without any surging or similar. I can confirm this from my own experience and from others who have finally set up their systems correctly and, where necessary, replaced faulty components such as sensors, ECUs, switches, plugs, or wiring.