My 80 911 has being running great this morning I go to start her and she fires right up but doesnt seem to clear up so I give her a little gas and she feels like she's running on 4 cylinder's. When she warmed up she felt better but still kind of rough I replaced plug's, wires cap and rotor she felt a little better but still not perfert, I just cant seem to figure out I had her out last night and it all started this morning any help or idea's thank you all

 

vacuum leak ? have you had a line pop off ?

 

Ernie: It sounds like the OXS/Frequency valve relay has failed. It's a small, square, silver relay under the passenger seat, close to the center tunnel, and is easy to see and change. The test: remove the air filter cover & filter. Turn on the ignition. Gently lift the sensor plate arm (inside the airbox) about an eigth to a quarter inch. You should hear the frequency valve, just forward of the throttle body, buzz loudly. No buzz? Replace that relay. If you have the buzz we have to go on to the next step...
Pete

 

Just tried what you reccomended Peter, and it does buzz ,so here I am asking again what else you all might think I did check for vaccum leaks and dont seem to see or hear any even with car running
it almost sounds and feels like ignition, I'm staying away from coil for now just dont want to keep adding parts and $ with out reaaly figuring out, although I am a Service Manager at a Lincoln dealership and have what I feel are a few qualified guys helping me with her they, I did take her last week to a repair facility to set co and spec's on her and like I said in my previuos post she was fine 1 night the next morning she began to act up like this the weather had dropped overnight to about 50deg from 80 durring the day so I am lost at this point thank you again for any help sorry for rambling I just like to explain the whole thing

 

Ernie,

The final version of CIS has several band aid additions to comply with emission tests and get a decent fuel curve. The system was only used for three years, there were several changes to fix the initial calibration, but Motronic came along and it was never fully sorted out. In 1981, another temperature sensor was added to increase cold running enrichment to fix cold running problems. In addition, the system cannot compensate as the engine wears and pull less vacuum. You cannot see or hear a vacuum leaks, you need to use a propane torch or carb cleaner around the injector sleeves and runner boots. If the injectors are loose and the O rings on the sleeves are original, they are probably leaking, the staked in sleeves do not seal as well as the screw type used by other OEM's. This system was calibrated on the lean side for a true cold start below 40F. If your symptom is that the engine fires, but stutters and stalls, but will restart and idle, two things are happening. When you crank the engine, the CSV injects the extra fuel to fire the engine, it starts, but the main mixture is too lean to keep it running smoothly. Feathering the throttle is the wrong thing to do, all you do is add air and increase the risk of a backfire. Your car also has a vacuum retard to meet the curb idle test. Once the car fires and creates vacuum, the ignition timing is retard at idle which can stall the engine. Other OEMs used temperature controlled vacuum switches to get around this issue. If you recently had the mixture and control pressure set and the engine has an initial stutter, try disconnecting and plugging the vacuum line on the back of the distributor (blue or gray). The idle speed will immediately increase and you need to reset it to 950 rpm with the large screw on the throttle body. This usually improves the cold start performance especially below 40F. The vacuum retard is strickly an emissions device and you can leave it disconnected, it has the side benefit of lowering temperatures while sitting at idle. You only get one chance a day to test a cold start so you need to be patient. I have also found the cold start better with Bosch normal spark plugs .

 

I don't think this is a cold start issue but a general performance issue, Given the fact that when it warms up it still runs rough. I could be wrong but that is what i read into it. I also thought CIS was used for 4 years from 78 - 81 but my facts could be off their also. But to keep things in perspective I run my car in Canada and it gets very cold here. We are into November now and I have the first gen CIS and the car starts and runs flawlessly. Something is wrong with your car and it is not a design issue. Definitely check for vac leaks but what you really need to do is check cold control pressure and running pressures. You need a fuel guage. It could be spark or fuel. Personally I keep a fuel pump in my garage and a coil. I consider these PM for my SC and a cost of ownership. Replacing these parts are not a waste but a preventitive measure, and you just might cure something , you never know.
Good luck.

 

Yes, you are wrong. CIS was used for 10 years, but like I said in my post, the final version, CIS lambda was only used for 3 years. I have mapped both the early and late SC versions with a gas analyzer for EFI calibration and the lambda version was leaned out considerably for emission control purposes. The initial calibration used in 1980 was not well sorted out, and Porsche added the extra switches, cold acceleration unit and dropped the cold pressure back to a setting closer to the earlier models to improve cold running performance. CIS is not like EFI, it needs a little skill to find the best compromise for each individual case.

 

er ....okay .....

so anyway Ernie , it runs well as designed so get the fuel pressures checked and if it is nothing obvious get a mech to check it out. The ignition modules can fail but it is an expensive part and you don't want to guess in this area. I have heard of head temp sensors causing some rough running probs too but if anyone has had that failure they will be able to chime in on their symptoms.

Since you did just have the car set up why not take it back there ? He may be able to give you a diagnosis since they just did work on it. You never know , it could be something simple like a cap or rotor.

Good luck and keep us in the loop.

 

Head temp sensor on a CIS car ?
Guess again.
CIS drivability problems are rarely cured by random part swapping, especially when the parts don't exist.

 

I was away this weekend just got back and will have one of my techs look at it today and I'll get back with more info thank you all for the input

 

ok had a friend stop by and look at the car he's a old Porsche guy he check a few things and say's that the lambda sensor is not working and the car in running to lean thats why its popping when you accelerate he did some checking and thinks the ECU took a dump so he's going to bring one he has at home later today and swap it out and I will report back thanks again for the help

 

Makes a lot of sense if the o2 sensor is leaning out the mixture. If that is it lucky you got to it early , lean running engines run VERY hot and can even risk burning valves. Hope it all works out for you .

 

If the lambda sensor has failed, the default setting is rich not lean. The purpose of the sensor is to dither the mixture around stoich at light throttle for converter operation and it is irrelevant to cold starting, cold running and throttle above 35%. The probability of burning a valve from a failed sensor is near zero, the high load mixture is controlled by the fuel distributor, as in all CIS systems. The system is easy to test if you have a dwell meter. There is a test plug behind the plastic cover in the left rear of the engine compartment, hook up the dwell meter to the green/stripe wire and a good ground. Start the engine, cold open loop reading should be a steady 85% duty cycle (76 dwell). When the engine reaches 15C degrees, a switch on the right side timing chain cover closes to ground and the dwell meter should start oscillating from 45-65% duty cycle (40-58 dwell). You can test the switch by grounding the wire. The sensor itself can be checked with a VOM, it should read 0.1-0.9 VDC when hot. My experience is that these cars run best with the mixture set at a 35-45 dwell reading. This mixture adjustment only effects the open loop performance, closed loop emissions and economy are the same because you are within the range of the system. This setting is closer to what Porsche changed for the 1981 MY system, after it discovered the faults of the initial K Jet lambda calibration.

 

First off my opology to Peter for my dumdness, it ended up being the oxs/frequency valve relay as he suggested. I tried what peter had suggested last Saturday (11/11) but I guess I had puched up on the throttle plate to much and what I had heard must have being the fuel pump running, but last night I was so frustrated and went back out and tried checking every thing again and sure enough I stuck my hand out behind the plate and thought that what I was hearing wasnt the same valve I was tuching so I kept playing with it then realised that the frequency valve was clicking went back to the relay did some test light checking and messing with the relay it started to click so I replugged it in and she fired right up beutifull thank you all again for the help I guess that's what happens when you get a dum Cuban working on a old German car.


Ernie

 

Wow so I guess in a way your budy was also right... doesn't the frequency valve have something to do with the sampling of the O2 sensor ? I can't remember the deatails as i don't have my manuals with me but I thought it had something to do with compensating for the O2 sensor when cold.