what would you check cis (its that time again)

[56 nomad]

hi guys, .....a reoccurring problem most of us have faced (thought i fixed it).
sorry for another in the long list of cis problems, i have a few questions and hoping for some insight.
some background ....83 sc with the dread ca. emissions looming.
I had a few vacuum leaks that i found and resolved, no oil leaks at the cylinders, good compression etc.
with the timing set at 5 degrees, (both vacuum lines plugged) car fires on the first click and idle gets higher (as it should) it just does not stay high long enough to keep the car from popping when cold and the idle drops to around 500 very rapidly.
adjusting the idle screw way out will change rpms but it sounds like there is too much air moving thought the system (to my untrained ear not as strong).
the car seems happier running more advance as the popping stops and idle is up.
what would you check in order of importance in the sequence, or should i just adjust the the throttle linkage?
popping in ca. ,dont flame me for asking ben

[56 nomad]

anyone????? regards, ben

[Targalid]

Since no one else has answered I will throw in my 2 cents. If the car does not hold a fast idle long enough you should check your fuel control pressures using a fuel pressure gauge connected between the WUR and the fuel distributor. A cold engine needs low fuel pressure (giving a rich mixture) at start up. Then the fuel control pressure rises gradually to full pressure which leans out the fuel mixture. Start with this first. If you have not already done so read this: CIS Primer for the Porsche 911
And the Bosch Factory Manual for CIS: Bosch K-Jetronic Fuel Injection Manual

[Bob Kontak]

I can screw my air bypass in all the way clockwise and the car will die. As I get closer to the clockwise stop it will chug at 200 rpm then stall. That can give you an indication of if you have vacuum leaks or not. If your car can idle at 600 you are sucking air. This is with everything set per standard timing and with car warm. I never tried it when cold.

I would perform a very thorough search for leaks as first order of business. Second would be to check your Aux Air Regulator to make sure it is open on cold start and then closes after a few minutes. Third is basic ignition (plugs wires timing) because it is simple. Then move to the fuel pressure test.

[56 nomad]

Originally Posted by Bob Kontak

I can screw my air bypass in all the way clockwise and the car will die. As I get closer to the clockwise stop it will chug at 200 rpm then stall. That can give you an indication of if you have vacuum leaks or not. If your car can idle at 600 you are sucking air. This is with everything set per standard timing and with car warm. I never tried it when cold.

I would perform a very thorough search for leaks as first order of business. Second would be to check your Aux Air Regulator to make sure it is open on cold start and then closes after a few minutes. Third is basic ignition (plugs wires timing) because it is simple. Then move to the fuel pressure test.

Hi Bob,
all new wires plugs etc.no vacuum leaks with propane check etc.
can you tell me how to check the auxiliary air regulator? have not read the cis primer is the information there?
regards and thanks for the assistance, ben

[psalt]

Ben,

Cold running problems are common on old CIS lambda engines, try searching the archives and reading abit, everything you need to know to resolve the problem can be found here. You are right about the advance, have you tried a cold start without the retard line connected ? CIS lambda is a band aid approach to squeek through the emission test before Motronic was ready. The hardest part of the OEM emissions test is the first two minutes and Porsche got it wrong on the first version of CIS lambda andf had to recalibrate the later version and add an extra ECU. My advice is to troubleshoot the ECUs, sensors and switches on your car, check the duty cycle open and closed loop and avoid "out in left" field guesses. With the correct knowledge and about 20 minutes with a dwell meter and volt meter you can establish the system is working properly , then make the adjustments than will give you the best cold running and WOT performance. You may have to reconnect the retard and reset the hot idle speed for the test, but it takes about 30 seconds.

[56 nomad]

Originally Posted by psalt

Ben,

Cold running problems are common on old CIS lambda engines, try searching the archives and reading abit, everything you need to know to resolve the problem can be found here. You are right about the advance, have you tried a cold start without the retard line connected ? CIS lambda is a band aid approach to squeek through the emission test before Motronic was ready. The hardest part of the OEM emissions test is the first two minutes and Porsche got it wrong on the first version of CIS lambda andf had to recalibrate the later version and add an extra ECU. My advice is to troubleshoot the ECUs, sensors and switches on your car, check the duty cycle open and closed loop and avoid "out in left" field guesses. With the correct knowledge and about 20 minutes with a dwell meter and volt meter you can establish the system is working properly , then make the adjustments than will give you the best cold running and WOT performance. You may have to reconnect the retard and reset the hot idle speed for the test, but it takes about 30 seconds.

Paul,
i have read many of the posts on the board (many by you) as well as some of the books etc. ...just trying to get a better handle on this.
i have tried running with the retard vaccum disconnected and i like it better but for smog out here in ca. it wont pass visual...are you asking for some other reason?
i would like to check the aar with the dwell and found several posts on this along with a great pic and located mine last eve, just do not know how to do the hookup and after that where to make the adjustment...is it at the fuel distributor or is there an adjustment at the aar?
as i think about it more i just recently had the cat replaced could the ox sensor be the culprit if it was damaged?
i will pull the seat to get a better look at the box and do some cleaning, checking connections etc.
thanks for your insight, ben

[psalt]

Ben,

It sounds like you need to do some reading on the CIS lambda system, my advice would be to read one of the BOSCH manuals, Probts book or the Bentley manual. Do you have a manual ? The vacuum retard is an emission device for meeting the curb idle HC test with the side effect of raising the engines temperature in traffic. The engine also has a much stronger cold running idle without it and many of the first start stumble and stalls with lambda CIS cars can be cured by disconnecting it. You do not check the aar with a dwell, you are checking the duty cycle of the frequency valve, which in closed loop gives you a good idea of the basic mixture setting. Basically, most cold running problems are caused by too lean mixtures, cold engines need a rich mixture, OEM emissions tests hate them. Modern EFI systems have active controls that can "catch" a stalling and stumbling engine with idle AIC motors and ECU ignition control, unfortunately CIS is a mess of separate components that can't talk to each other. You need to find the best settings for your engine in it's stage of life because CIS can't make those adjustments. The O2 sensor is irrelevent to a cold start and once the engine fires, the cold start valve and TTS are also irrelevent. The aar is not adjustable and if you idle is high at first then drops it is probably working. You should first determine if the lambda system is working, and where the mixture is set, the dwell meter will tell you this. Your car has an extra ECU that runs off a temperature switch and a throttle switch to reduce cold acceleration stumbles. Is it working ?

[56 nomad]

Originally Posted by psalt

Ben, You should first determine if the lambda system is working, and where the mixture is set, the dwell meter will tell you this. Your car has an extra ECU that runs off a temperature switch and a throttle switch to reduce cold acceleration stumbles. Is it working ?

paul,
thanks for following up me and enduring my "simple and uninformed questions"(LOL) It was my mistake and miscommunication about aar as it was 430 in am here as i was more concerned about the lambda you spoke about in your other posts and checking that...let me ask one simple question if i may..."how" does one check the lambda sensor...can you explain to me the procedure ie. hook ground of dwell to (which leads).. then check reading if too high or low adjust (what and where) ... if i need to read the bosh cis manual again that says check this it gets me back to the question of "how".
if there is a manual that covers all this it i will buy it but if you or anyone else could answer this question i could at least start there and move on until my new reading material arrives.
thanks again, thick headed ben

[56 nomad]

thanks to all that offered help,
i received a response from a fellow pelican, bob kontak. he directed me to what i hope is a sticky..if not it should be! this is the thread for those with some similar issues. i learned a lot from reading it .
i have the bently as well as bosh tech stuff but mostly directives to check the sensor or adjust the unit , very little mention as to the "how" ....this thread gives direction/procedures etc..for me very helpful. "911 sc starting issue" ( for some reason not coming up blue)
regards to all, ben

[Bob Kontak]

Originally Posted by 56 nomad

he directed me to what i hope is a sticky..if not it should be! this is the thread for those with some similar issues.

It is a thread with 225 responses. The OP, scott.k, God bless him, took the good part of 2011 to get a very few bugs worked out of his CIS system. Everybody, including the smart guys, tried helping him from all kinds of different angles. Some good wrestling matches and a bit of screaming finally got the car running. In between all of that there is a massive amount of data. The CIS Primer is linked in there as well.

911 sc starting issue

[T77911S]

dont mess with the linkage.

if you need it to idle high longer, try removing the connector on the AAR. it then would be controlled entirely by engine tmep, which may make it take too long to idle down. i have never tested this to see how long it takes.

advancing the timing at idle richens it up, that is getting rid of the lean popping.

follow what psalt says and get the lambda stuff working.

just curious, what plugs are you using? DO NOT use the bosch platinums.