What is CIS
 

Hi everyone, would someone be so kind as to explain CIS vs non. I THINK it means Continuous Injection System. But does that mean carbs or mechincal injector?? I know its not electionic injection. Thanks this would make me feel a little less, ummm clueless.

Mike

Actually, it is not Carbs, and I am pretty sure it is electronic FI. It is the system that came on 3.0 SC's (and maybe the 2.7's). I don't know much beyond that, but someone else will soon chime in with details.

CIS is the common name used for the Bosch K-Jetronic injection system. CIS does stand for constant injection system. It is not electronic (well, except for the pump which is powered by electricity). Here's a site that gives a pretty good description of the components and operation of the K-Jetronic system.

Good luck,

Jerry M
'78 SC

check this out

http://www.phat-gti.com/downloads/boschtech-12d.pdf

Try these sites:

http://www.auto-solve.com/mech_inj.htm

http://www.users.bigpond.com/INTERJECT/KSITEPLN.HTM

Basically put, k-jetronic is a simplifed version of mechnical injection where the metering pump is replaced by a mechanical flow sensor that adjusts a valve to meter fuel into the cylinders.

Yep, there's no lambda sensor or computer in these cars. Airflow into the airbox is what varies the position of the mechanical sensor. This is what meters the fuel flow which is ALWAYS flowing at one rate or another, depending.
Ryan

My 1980 SC has a lambda sensor on the CIS system, the earlier ones don't.

Mike,

Welcome to the board. We are all clueless, it's just that some have more clues from experience than others! (I'm waiting the flames now ;) )

Gerald,
My bad...I knew that. Guess I was thinking early CIS because his car is a '73...
Ryan

The 80 SC was the first year that the K-jetronics CIS with lambda was installled. 78SC and 79SC had just the k-jetronics CIS.

CIS is a hydraulically operated fuel injection system used on 911s from 1973.5 to 1983(?) when it was replaced by the Carrera's DME system. It is neither electronic nor mechanical, but uses vacuum. In its day, it was good for both emissions and economy, and was widely used on Eurp-peon cars. For a sports car, it is the work of the Devil and ought to be removed at once (if your state emissions laws allow that). It has horrible throttle response and does not make much power.

Here is a Site thats helped me out of several Pickles..
http://members.rennlist.com/jimwms/CIS/CIShome.html

Jorge (Targa Dude)

Sir,

I beg to differ. CIS uses a plate in the incoming air stream to detect and measure the incoming air flow rate. The plate is connected to a teeter-totter mechanism that adjusts a needle vlave to determine the fuel flow rate. There is no vacuum on this unit. Vacuum is used for various ancillary bits to "tune" the basic unit.

Much of the power loss problem with CIS is due to the lack of allowable valve overlap, which affects air and exhust gas management.

Respectfully submitted.SmileWavy

We agree. It is the vacuum in the air stream that causes that metal plate to move.

Unfortunately it has a lot of inertia.

And, yes, the CIS system requires the screwed up valve/piston items.
Put on PMOs if at all possible is my advice.

Check out this website (systemsc.com).
It may be helpful for answering Porsche
fuel injection and ignition questions.

See ya
Lorenfb@aol.com

wasn't the original cis replaced by cis-e with the o2 sensor, basically upgrading it from hydro-mechanical injection to elctronically controlled hydro-machanical injection?

The lambda system is simply a piggy-back system where the electronic feedback can adjust control pressure via the frequency valve to change the mixture. So it's a form of mechanical injection that has an electronic device added on to more accurately meter fuel.