Testing 82SC CIS Lambda Brain
 

I have decided to hook up my O2 sensor and play with the stock set up to see what I can get for gas mileage. I have searched and invested many hours of reading and feel I have a good understanding of the CIS system. For background I have replaced all rubber relating to the system when I did the engine rebuild and do not have any vacuum leaks. I had my CO set to 3.5 at a local shop and car runs well OPEN LOOP and I do not have any issues but I just want to give the Lambda system a shot. I have tested system and control pressures and WUR is in spec.

My first impression with O2 plugged with CO still set 3.5 is a chugging effect with light throttle at constant speeds. This chugging is not bad and I have heard it described like pulling a trailer ( push pull thing.) One good thing is I do not have as much of a rich smell at idle because Lambda is pulling mixture lean at idle (? 45-50?).

As for testing I have a MAC EM710 digital volt meter that has both dwell and duty cycle settings. With all testing done with + at the green and white wire at test port and – grounded to engine I get 50% duty cycle with open loop I get 50% (normal). With car cold I do not get the 65% duty cycle but it is 80 degrees here so the cold start switch is not grounded because it is too hot. If I ground the wire for the switch I do get 65% cold start value. The only thing that has me scratching my head is if I ground the Lambda O2 wire I do not get 90% I get 70 or so. Because I do not get the 90% with Lambda wire grounded does this point to the brain? If it is the brain could this be the reason for chugging effect?

I think your going to have to put your co back to the original spec for lamda control, i tried it and got the same effects, maybe worse, lowerd it just enough for the 02 to keep at stoiche, ( d/meter should be bouncing around 40 to 60)and ran great.

Don, I thought 3.5 was the CO spec, no?

Thanks for any input here.

only if you've disconnected the lambda, put it down to 1.5 and try it there. if your frequency valve is getting a duty cycle from the ecm, it will correct to stoich at idle and part throttle.

Looking for duty cycle or dwell numbers how does one get to 1.5? As for now mine was set for 3.5 but has a duty cycle close to 50% closed loop. If I start to lean it out will the duty cycle change or would it stay around 50% until the 1.5 range and climb after that?

my car and other 02 cars Ive adjusted runs their best when i adjust the co screw (as rich as possible) until 02 cant compensate any more, that way you will still have a stoiche idle and good fuel economy, and still have the mix rich when in open loop. this also makes advancing your timing to where it should be (32-36 max advance) a little more worry free.

I guess my big question is the surging at part throttle. Because mixture was set for 3.5 OPEN LOOP and now I'm in closed loop is the mixture too rich? I tested voltage at O2 and have .88 and from what I understand this is on the rich side. Even with this thing this rich I get the duty cycle of 49-51. What will happen to the duty cycle if I start to lean it out? I guess my question is does the mixture screw (not air bypass) have a direct effect on duty cycle?

yes, your mix screw has an effect on duty cycle. if the mix is to lean, the duty cycle will go up, trying to relieve the pressure in the lower chambers of the fuel dist, which richen the mix, if to rich, the cycle will go down. also test your frequency valve by cracking the 35 degree throttle switch, duty cycle should go to around 90 for maximum wot enrichment. lot of variables for getting the correct mix on any certain car (atmospheric conditions, timing, engine mods) correct, are you sure yet that your lambda control is in good working condition? you can get a bosch 1 wire 02 at o'reilly part store for 20 bucks, and you must use the correct metal bosche relay under the seat, (another 20 bucks)those plastic 5 pin part store relays look the same but are not.

I have adjusted mixture slightly with duty cycle spot on 50% 2/3rds of the time with a slight tick up 51% and a slight tick down 48%. I went for a test drive and the slight chugging (push pull feeling) is much much better. My O2 sensor is new and working as far as I can test currently .78 on voltage with current mixture setting.

One major factor could be the relay. Mine went bad a year or so ago and I bought a black plastic one from Napa. The Napa relay has worked but I have had Lambda set for open loop and now that I want closed loop relay could be a factor. Lambda seems to work fine but I never can get 90% with grounding.

When I test the throttle switch it only will go to 65%

After some testing I have found that I get 65% with and without enrichment control box plugged in wile testing over 35% throttle.

with engine running put your hand on the fre/valve to make sure it is buzzing, if not, clean the grounds under the seat good, check the main harness gang connector that is behind your heater blower motor, (the lambda has a separate harnesss from the main engine harnesss). unplug it and spay electro cleaner in it.http://forums.pelicanparts.com/uploa...1248357113.jpg

bookmark

Here's all you need:
https://nineelevenheaven-wordpress-com.translate.goog/der-911-us-sc-3-0-motor-mit-g-kat/?_x_tr_sl=de&_x_tr_tl=en&_x_tr_hl=de

https://nineelevenheaven-wordpress-com.translate.goog/abgasregelung-beim-sc/?_x_tr_sl=de&_x_tr_tl=en&_x_tr_hl=de

(Translated viy Google)


EDIT: uops, sorry I just recognised the Thread is from 2009!
Don't know why Porschedude just posted a "bookmark"

I wanted to save interesting reading and information on CIS.