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SC Lambda questions

After doind many searches and reading TONS of posts, I decided to follow a select few's suggestion to disconnect the 02 sensor on my '80 Sc.
I immediately noticed a dramatic increase in power, smoothness and drivability of the car over a broad rpm range.

Question 1: can the lambda system be completely removed from the vehicle?
This leads to question 2: where exactly is the frequency valve and, can it also be removed from the system without having to swap out the entire CIS to an earlier unit?

I do NOT want to convert to EFI !
The CIS WILL remain !

Souk, Tsuter.......THANK YOU BOTH FOR MANY VERY INFORMING HOURS OF READING !!!!
I hope to have the chance to down a few cold ones with either of you someday !!!!
Old 01-31-2006, 04:03 AM
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1. Yes, anything is possible but it would invlove changing out a lot of components to do it right. It is not simply an "extra" added to a normal CIS system. You'd want to get a parts CD and compare what your car has with what parts are on the car you are trying to emulate, to get an idea of what parts to change. There were many, many little differences in the CIS cars from year to year and market to market. I would suggest sticking to a combination of parts that Porsche engineered to work together. Sort of pointless, if you ask me.

2. The frequency valve is located near the fuel distributor. It is a black cylindrical thing with a silver band in the middle and has a steel fuel line going in one end and a rubber hose at the other. There is also an electrical connector attached at an angle to the top, much like a cold start injector. When you disconnect the O2 sensor, the frequency valve is still in use. The control module sends a fixed duty cyle to it. So no, you shouldn't just yank it out.

If you run without an O2 sensor, make sure that you have your CO set properly.

JR
Old 01-31-2006, 05:56 AM
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The frequency valve is about 4" to the left (driver's side) of the throttle body, about 4" above the fiberglass shroud.
The lambda system is designed to keep your mixture close to stoich (14.7 to one) all the time except at full throttle and during cold start and warm up.
If you leave it connected and everything is adjusted and functioning correctly, your engine will run clean, smooth, and with near maximum efficiency. If you disconnect it and adjust the CO to around 3 to 3.5, you will get more power and sacrifice economy and clean running.

Why do you want to remove it completely? I see no reason to remove it, just disconnect the O2 sensor and the frequency valve goes to default setting. then adjust for CO and you are there if that is what you are after.
Old 01-31-2006, 06:36 AM
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To give you a data point on O2 sensor operation, here's an interesting mix for you:

I bought a 1969 911E with a 1979 3.0 liter engine and a 1980 fuel injection. It took me a few weeks to sort out what I have but this is what I noticed...

-There is no 15 degree switch on the right valve chain cover. Since it's a '79 engine, the cover was never tapped for the temp sensor.
-The O2 sensor wire is disconnected because without the 15 degree switch the O2 sensor is worthless. Since there is no 15 degree switch then there is always zero volts to the lamba brain. The brain would always think the engine was cold and always try to richen the mixture.
-My frequency valve is directly between the throttle body and the firewall. Not too sure if that is the standard location.
-I recently changed the plugs and they were dry and black with soot indicating a rich mixture.
-Initial start when it's cold is a bit rough but smooths out within a minute.
-It runs strong and smooth when warm.

I am going to borrow an exhaust gas analyzer and lean the mixture out some.

I plan on tapping the valve chain cover, installing the temp switch and reinstalling the O2 sensor...eventually. I want to see the difference.

Hope this helps. I don't think the O2 sensor is terribly important. If I were to use her as a daily driver, then for the sake of fuel economy I'd have the O2 sensor. But for a few hundred miles per year, I'm not too worried.
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Old 01-31-2006, 07:20 AM
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Quote:
Originally posted by divezic

-The O2 sensor wire is disconnected because without the 15 degree switch the O2 sensor is worthless. Since there is no 15 degree switch then there is always zero volts to the lamba brain. The brain would always think the engine was cold and always try to richen the mixture.
I think you'll find it is the other way around. I believe the 15 degree switch is closed when the engine is cold (lambda box signals a rich mixture to the FV), and opens above 15 degrees (signals the ECU to go closed loop with the O2 sensor). So if there is no switch there (open circuit), the engine never gets the rich cold start mixture, and will always be the O2 mode.

I tried to verify this with a used 15 degree switch I have in the parts box, but I couldn't get a closed circuit at room temperature, or even with running cold tap water over it which should have brought it down to 60 degrees F (roughly 15 degrees C). (Later I revisited this issue, and used a cup of water with a couple of ice cubes bringing the water temp down to 40 degrees F and got a switch closure.)
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Last edited by Jim Williams; 01-31-2006 at 06:51 PM..
Old 01-31-2006, 03:23 PM
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Still the question remains, can the frequency valve be eliminated from the system ???
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Old 01-31-2006, 04:36 PM
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In a word.... No.

The fuel distributor for the '80 and on was intended to utilize the frequency valve to make the mixture adjustments for warmup, closed loop with the O2 sensor, and enrichment for acceleration and Wide Open Throttle (WOT). You can disconnect the O2 sensor and still have an operable system. If you remove and plug off the FV, you also lose the warmup enrichment, and acceleration and WOT enrichment.

The Warmup Regulator that came as stock with the '80 does not provide the enrichment functions associated with the manifold pressure changes of earlier systems. So you will now be faced with at least swapping out the WUR for one that provides mixture adjustment. I am sure others have actually tried this, but I don't have personal knowledge of the results. Maybe someone who has actually done it rather than guess at it will post their results.
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Old 01-31-2006, 05:07 PM
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Yes, you could eliminate the frequency valve.
Yes, it would be a major PITA and would require changing all kinds of parts and spending lots of money, basically backdating your entire CIS system to a 79 or earlier.
No, it isn't necessary or worth it.

Once again, why would you want to do it?
Old 01-31-2006, 05:14 PM
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OK, let me stray off just a bit.
I plan to turbocharge this car at some later date.
Would the Lambda system (if functioning correctly) be able to enrichen the A/F mix during boost so as not to require the addition of an enrichening injector system ?

My experience of better performance with the 02 sensor unplugged, i assume, is due to the lambda system not functioning correctly OR is it that the lambda system IS functioning correctly and the motor just enjoys being richened up, above the A/F ratio that the lambda is designed to provide?
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Old 01-31-2006, 05:17 PM
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Paslantnose..!

Let me tell you .. The FV in my Porsche was disconected in the past by a nasty mechanic and let me tell you , It was a nigthmare man.
Like Jim W . says don't disconect the FV, you wil l have a hell of a time. If you want to experience the behaivior of a 3.0 without the FV just disconect the electrical lead that goes to the FV and run the car. You'll see.Man

Vic
Old 01-31-2006, 05:17 PM
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My reason for wanting to eliminate the FV (IF i went that route), would be to do a "clean" removal rather than have stuff such as the 02 sensor sitting there unplugged.
For instance, say on a chevy some people just remove the AIR pump's belt. I would go all the way and remove the pump, control system and exchange the exhaust manifolds for ones without AIR tube holes JUST to make it a sanitary change with no remnants left as eye sores.

As it has become evident that removing the FV properly would require backdating the entire CIS, that is what i would do if so inclined to eliminate the lambda system.
Do it ALL or not at all mentality.

Don't get the wrong impression, i might just as well be inclined to restore the lambda system to 100% correct and functional operation.
For now, the car really likes the 02 sensor unplugged. Give the motor what it wants !
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Last edited by paslantnose; 01-31-2006 at 05:36 PM..
Old 01-31-2006, 05:27 PM
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Quote:
Originally posted by paslantnose
OK, let me stray off just a bit.
I plan to turbocharge this car at some later date.
Would the Lambda system (if functioning correctly) be able to enrichen the A/F mix during boost so as not to require the addition of an enrichening injector system ?
On this issue, you might contact Stephen Kasper at Imagine Auto. I understand he has worked with a CIS parts rebuilder to do the kind of thing you are talking about. He might be able to help you get the right answer to your question.
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Old 01-31-2006, 06:59 PM
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Quote:
Originally posted by paslantnose
OK, let me stray off just a bit.
I plan to turbocharge this car at some later date.
Would the Lambda system (if functioning correctly) be able to enrichen the A/F mix during boost so as not to require the addition of an enrichening injector system ?

The Innovate LM-1 or LC-1 can do this to some extent. Do a search on LM-1 and CIS and you'll find that you can hook up the LM-1 to make the Lamba system go rich (or whatever A/F ratio you want) under full throttle.
Old 02-01-2006, 04:28 AM
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With the O2 sensor plugged in and functioning correctly, it will control the mixture corrctly, but at full throttle it is designed to go richer.
One thing I did was to hook up a hobbs switch that senses positive intake manifold pressure (turbo) and basically grounds the O2 sensor wire to the chassis under boost. that forces the lambda brain to tell the FV to go richer.
That will provide enough fuel for 7 psi boost, maybe a little higher if you are intercooled but not much. If you plan to go much higher than that, you will need to do something to provide more fuel or to reduce ignition timing, or both.
There comes a point (below 12 to 1) where more fuel will slow the burn and reduce the chance of pinging, but gives away torque, horsepower and economy.
In that case you would be better off with retarded timing instead of going too rich.
if your plan is to run more than 7 or 8 psi boost with pump gas you will have to either get creative or live on the ragged edge.

I just hooked up my LM-1 and am still getting familiar with all the functions so I haven't yet figured out exactly how to use it to re-program the fuel mapping on CIS.
My plan if I ever go higher with the boost will be to control pinging with timing, not extra fuel.
Old 02-01-2006, 05:51 AM
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Quote:

My plan if I ever go higher with the boost will be to control pinging with timing, not extra fuel.
How do you plan on controlling timing? I've been wondering about a good way to be able to control timing on a CIS car.

Thanks,
-Scott

Last edited by PcarPhil; 02-01-2006 at 06:01 AM..
Old 02-01-2006, 05:57 AM
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sammyg2, now THAT was the info i was looking for !!!
With mine being a 1980 SC with the 9.xx CR, i have been informed that 6-7 # of boost would be a safe limit.
With that, and what you say about the lambda being made to go "full rich" via a pressure switch, the whole setup should work pretty well without having to add an enrichment injector correct ???
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Old 02-01-2006, 06:19 AM
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Kaefer, i know that the MSD ignition control (6AL) will accept the addition of a timing retard module.
Those module are normally activated by rpm or pressure switches so handling timing retard is very simple.
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Old 02-01-2006, 06:22 AM
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Can the mixture be changed mechanically? I have a Scirocco with CIS and I eliminated the O2 sensor and had the mixture at idle adjusted (3mm allen screw in the air vane). It runs great and still gets great gas mileage. I know it isn't a 6 cylinder but the technology is the same. You don't want to eliminate the FV because that controls the fuel mixture. Usually it takes inputs from the O2 sensor but it will default to a middle of the road duty cycle when disconnected from the O2 sensor.
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Old 02-01-2006, 06:40 AM
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Hi,

As to removing the Lambda system:

The metering valves in a fuel distributor (small plate valves) control the fuel flow vs. pressure for each injector. They are spring loaded and have a lower chamber, connected to the control pressure. On a pre-Lambda system they have a fixed bleed orifice to the fuel return. On a Lambda system that bleed orifice is replaced by the frequency valve. When the FV is open, more pressure is bleeded from the lower chambers and more fuel is metered to the injectors. If the frequency valve is closed, the chamber pressure is high and the engine leans out. If you remove the FV and plug the line, the engine would run so lean that it would barely run at all. If you leave the line open the engine would run so rich it would also not run well.

The Lambda 'brain' opens and closes the FV about 50 times/second with varying duty cycle. That duty cycle controls therefore the bleed ratio of the lower chamber.

When the O2 sensor is disconnected, the Lambda controller defaults to about 50% duty cycle during idle and part throttle. When the WOT switch closes (or the 15 degC switch closes) the lambda brain runs a constant duty cycle of about 60% (varies depending on engine) and ignores the O2. When the O2 sensor is connected, the controller regulates the duty cycle such that the O2 sensor voltage is about 0.45V.

Regards,
Klaus
Old 02-01-2006, 09:06 AM
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Good info Klaus. BTW, i am very happy so far with the LM-1.
I have a question for you though, I have been told that grounding the lamda sensor wire will fool the FV to go rich also. Is that basically the same thing that the WOT switch is doing or will grounding the wire make it go even richer than at WOT?

paslantnose, The stock CIS will add enough fuel in a turbo application up to around 5 or 6 psi with no additional enrichment or tinkering needed. The original BAE kit was designed to bolt onto a stock engine and run 5 psi with no FI mods.
Above 5 or 6, extra fuel is usually added or timing advance is taken out to prevent pinging.

So if the dizzy was modified or the ignition mapped to take out about 5 degrees or so of advance under boost, the stock CIS would be more than capable of correctly metering the right amount of fuel with 7 psi, maybe 8, maybe higher. I haven't done enough testing to find out where that threshold is.

BTW, a 1980 3 liter engine with 7 psi boost is loads of fun and safe for the engine, as long as it doesn't run lean or have too much ignition advance. You may find that is all the power you need.
Old 02-01-2006, 09:42 AM
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