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.

[massmike]

So Tony has been through this WUR in August of this year. He listed a warm control pressure of 52psi. I am wondering if my cheap gauge set is not 100% accurate, since I am reading 49-50Psi.

Also for my knowledge, does 1-2psi make that much of a difference to a CIS system?

[ahh911]

Looks like 090 wur.

I have the same one, took the warm control pressure from 3.4 to 3.6 bar, didn't notice much difference. My notebook is at home..

How was this test quickly performed without knocking the big round thing up or down? To increase the warm control pressure I simply placed a small shim made up of beer can tin under the spring if I remember correctly. How did I lower it? I placed shims between the wur case halves, made of beer can tin stacked on top so I could increase the range in steps. Got all the range I needed to test how the car would respond and used a fuel pressure gauge of course.


Edit:
For what it's worth, I have my notes in front of me now:

System: 5bar.
WCP with 0.3mm spacer between wur case halves 3bar
WCP with 0.2mm spacer between wur halves 3.2 bar, My notes are barely understandable but I did write, 2000 to 3000 rpm surge. 02 sensor ~ 58% (probably increased 8% from 0.3mm)
WCP with 1 shim, 0.1mm, 3.3 bar. FV duty average moved from 58 to 67% (reset mixture to 50% before next step).
WCP with no shim, 3.4 bar, O2 duty cycle went from 50 to 57%.

These notes are hard to decode, so I wouldn't bet on the above being 100% accurate, but we can see that the o2 system is jacking up the fuel as the WCP is increased, by about 8% per 0.1mm.

In my notes, I wrote that 3.2bar to 3.4bar made little difference, maybe at high rpm. I went higher control pressure but wasn't interested in that.
I don't think 3.4 or 3.5 bar is going to matter once the mixture is set correctly, but I can't be sure. Have you checked your gauge calibration? It's easy to be off 0.1 bar.

Phil

[mysocal911]

Originally Posted by massmike

So Tony has been through this WUR in August of this year. He listed a warm control pressure of 52psi. I am wondering if my cheap gauge set is not 100% accurate, since I am reading 49-50Psi.

Also for my knowledge, does 1-2psi make that much of a difference to a CIS system?

Remember, you have very a subtle problem which may be attributable to the control pressure being too low in closed loop.
Try changing it. You can always readjust it back.

The key point with your CIS system is once the O2 sensor is connected, the system becomes a closed loop servo, having positive feedback will cause
oscillations, i.e. surging. The solution to servo systems with positive feedback is to reduce the feedback, reduce the input signal (O2), the system signal gain,
or the feedback signal phase. It's not always a simple solution.

[mysocal911]

Originally Posted by ahh911

Looks like 090 wur.

I have the same one, took the warm control pressure from 3.4 to 3.6 bar, didn't notice much difference. My notebook is at home..

How was this test quickly performed without knocking the big round thing up or down? To increase the warm control pressure I simply placed a small shim made up of beer can tin under the spring if I remember correctly. How did I lower it? I placed shims between the wur case halves, made of beer can tin stacked on top so I could increase the range in steps. Got all the range I needed to test how the car would respond and used a fuel pressure gauge of course.


Edit:
For what it's worth, I have my notes in front of me now:

System: 5bar.
WCP with 0.3mm spacer between wur case halves 3bar
WCP with 0.2mm spacer between wur halves 3.2 bar, My notes are barely understandable but I did write, 2000 to 3000 rpm surge. 02 sensor ~ 58% (probably increased 8% from 0.3mm)
WCP with 1 shim, 0.1mm, 3.3 bar. FV duty average moved from 58 to 67% (reset mixture to 50% before next step).
WCP with no shim, 3.4 bar, O2 duty cycle went from 50 to 57%.

These notes are hard to decode, so I wouldn't bet on the above being 100% accurate, but we can see that the o2 system is jacking up the fuel as the WCP is increased, by about 8% per 0.1mm.

In my notes, I wrote that 3.2bar to 3.4bar made little difference.
I also increased the system pressure a little and achieved 3.5bar, not a whole lot of difference either. Overall wcp did something, but not a heck of a lot was the end result. I don't think 3.4 or 3.5 bar is going to matter once the mixture is set using a professional meter. Go to a garage and have the mixture adjusted using the co and checking for excessive hydrocarbons. A bigger picture may emerge. Sorry for the trouble you're experiencing, it's not fun.

Phil

Thanks, excellent data! Hopefully, it will give the OP a better understanding of the effect of the WCP.

[AndrewCologne]

That’s normal, since –with the same initial CO setting kept– a warmer control pressure from the WUR makes the mixture result leaner, and therefore the duty cycle will rise to compensate this.
But here we’re still talking about constant pressure readings, correct? No pressure oscillation?
Because a non-constant system- or warm control pressure, and therefore a non-constant mixture, will cause surging.

Many years ago in Germany, there was a retrofit kit available that added a catalytic converter including lambda control to a 930.10/204 hp ROW engine so it could obtain Euro emissions classification here in Germany.
The lambda control was based on an oxygen sensor and a special ECU that regulated warm control pressure using a solenoid valve (similar to the frequency valve) in order to achieve lambda 1 in the mixture formation.

[ahh911]

Dave the surging I felt would have been much stronger then what massmike is talking about. I should have noted that originally. I just put the data online for reasons I'm not even sure of except that you can increase the wcp easily using tin under the spring for temporary study. Maybe massmike and Tony have different calibrations, even then it's not too tough to temporarily modify the wcp out of interest.

Phil