CIS Surging Under Constant load

[AndrewCologne]

@massmike
Here you can see what a poor lambda reading looks like and what Dave and I are referring to:



The amplitude is high, which can cause surging when the amplitude/reading remains at a high level for too long.


And here is how it should look:



Lower amplitude during oscillation = lower duty cycle amplitude = fewer low chamber pressure changes (in the fuel distributor) required via the frequency valve.

@Dave
The fuel control pressure is almost not affected by the flow in the frequency valve; the valve regulates the system pressure in the lower chambers of the fuel distributor. The higher the pressure in the lower chambers pushing upward against the diaphragm, the less the inlets above the membrane open toward the lines leading to the injection valves.

[mysocal911]

Post #1:

Originally Posted by massmike

Looking for some help to solve a problem I have been chasing for a few months now. Car is a 1982 911SC with a 3.0L and the original CIS system. My issue is when the car is running in closed loop there is a light surging at cruising speeds. The surging can't be seen on the tach but I find it incredibly annoying to drive it like this. If the O2 sensor is disconnect the surging completely goes away, so I believe this problem is limited to the Lambda system. I do have an LM-2 wideband connected and with the O2 Sensor disconnected I see 14.3 - 14.5 while cruising, O2 sensor connected I see it jumping between 14.3 and 15.3 at the same RPM and speed range.

I have replaced the O2 sensor and the FV relay, both made no difference. I have also adjusted the mixture several times with no noticeable change in the surging. I am thinking possibly an issue with the Lambda ECU??

Any help would be greatly appreciated.

Your data from your first post is potentially insightful. It indicates your warm control pressure may be a little too low (causing a too rich a mixture).
An upstream post suggested checking the warm control pressure. Have you checked it to the posted WUR specs?
This can potentially contribute to the closed loop O2 system developing a greater Lambda correction - surging,
as the system attempts to over-correct (15.3)



To lean the mixture, the pin needs to move up.

[AndrewCologne]

Please check the instructions in the link:
https://nineelevenheaven.wordpress.com/adjusting-the-warm-up-regulator/

Moving the small pin adjusts the cold control pressure, while moving the large dark component with the connections changes the warm control pressure.

But if you mike don't have the skills, just ask Tony.