SC owners. CIS. What have you had to tune/adjust for CIS ?
 

tl;dr
Can the SC owners detail what issues they've had with CIS,
and what they had to do to resolve it ?

Why am I asking?

In any new thread, prospective air cooled buyers are always told the same thing.

Avoid carbs. Carbs bad! FI good!
Avoid SC. CIS bad! Motronic good!
Avoid 915. 915 bad! G50 good!

So, everyone is always told to by the same thing: 1987-89 911
Seems like a good way to pass up an otherwise great car.

CIS gets a bad wrap. Some of it is deserved and some of it is undeserved. Some people have experience with carbs. Even if you don’t have experience with carbs there are plenty of people who do understand carbs. Same goes for EFI. CIS doesn’t have the same universality, so if you want it fixed right you have to commit yourself to understanding how it works. Some people aren’t willing to do that.

A common issue I see with people troubleshooting CIS is the expectation that there is a singular smoking gun when it comes to finding and fixing problems. They expect that if they can find one easy thing all their problems will go away. The reality is that CIS cars often have more than one problem. People who end up owning CIS cars often inherit cars where some maintenance has been ignored. Rather than finding and fixing the underlying problem, some previous owner or mechanic treats the symptoms instead. For example, continuing to tweak up the idle AFR when there is a slowly worsening vac leak. We’ve had shops post here asking questions about a customer car. And what they’ve done first is usually swap some expernsive parts with no methodical troubleshooting.

CIS cars run great when they are working as designed. But if a prospective buyer is an instant gratification kind of person, CIS is not for them. But the opportunity is there for people who have patience.

A downside of CIS/SCs compared to the late Carreras is that if you want cheap HP gains, CIS isn’t really an option. You can change the exhaust and put a Steve Wong chip in a Motronic for pretty cheap. There really isn’t such an option for a CIS car.

I think that tirwin did a nice job of critiquing CIS. I cannot stress enough, that someone must study/learn CIS if you are going to successfully work on it. The addition of a wide band air/fuel ratio gauge has been a great help to me in seeing what my system is doing at any point in time and in tuning.

Dave

Forgetting DIY, it seems like the right advice to a prospective SC buyer is to make sure your local Porsche mechanics knows how to service CIS ?

I have hand no problems with the several CIS cars I have owned. Once they are working properly, they are mighty reliable despite their lack of simplicity. Measure fuel pressures if you want, though they are likely correct. Clean injectors. Set the mixture using a sniffer in the tailpipe, and then find something else to worry about.

My bimetal strip in the WUR failed so the control pressures would not change with time and temp. Once it was changed and the control pressures rest, it worked correctly.

I also had an extremely thin spot worn in an aluminum tube that carries vacuum. I don't know if it actually leaked, but it certainly was about to. I patched it and everything seems fine.

I've had two CIS Porsche's...both '83 SC's one US 930-16 and the present ROW 930-10.

I've had no issues with either system but they are obviously dif.... with either system the best thing one can do imo is put an onboard wideband AFR gauge in the car …. you will then know if everything is working correctly as one can adjust to compensate for an issue and not get the performance one wants.
e.g. When I got the ROW it would lean out on hard acceleration....not dangerously so but enough....that should not happen.
The mixture is controlled on the ROW by the WUR...once rebuilt...nice mid 11's on hard accel.
The AFR adjustment had been enriched to compensate for an out of spec WUR....

Both ran flawlessly tho and the 930-16 had 230k miles....I've put another 40k on the ROW with no issues at all.

Once you get the system it works efficiently and with good mileage.

I will change over to ITB's if the system ever croaks....presently, it works too well to mess with on the ROW.

I got the car 4 years now, 81 SC. usa model.

CIS drove good, i have nothing really bad to say about how it drives...when it runs properly. I loved driving it, MUCH more fun than my 1969 T on carbs.

then winter came, and i noticed that my WUR wasn't working properly, impossible cold starts, started learning about jetronic, WUR fixed, then i had other cold start issues, chased it for months until i found a block off plate in the CSV flange.
The car seemed to run fine, until i put on a wideband gauge and noticed pretty awful AFR's.
Started digging further into the whole system...WUR still not good, AAR not working 100%, lambda system not doing what it should do, etc

honestly, 81-83 USA CIS cars are a complete mess, and are ridiculously hard and expensive to troubleshoot and fix. You got that whole array of stupid bandaid junk and overcomplication (AAR, AAV, decel valve, etc etc etc) and the lambda brain is a big black magic box which nobody knows how to fix or check. 78-79 cars are a little bit better i presume.

I bit the bullet 2 years ago: i decided to not spend another dime on an old and flawed fuel intake system (no new parts available and super expensive crappy second hand parts) and changed over to Bitz kit, installed it in a couple of days, tuned it on a dyno, and drove 1,5 years without any issues, loved it. -10°C starts each and every time.

Last month, my old distributor failed, no way i'm buying a 40 year old 2nd hand dizzy for 1500 €, and i swapped to full EFI with distributorless ignition. Got the car running from the first crank. I am not looking back, screw resale value, screw originality...i just want to use this car and drive the hell out of it, not worry all the time when the next 2000€ thing will break. Gimme modern reliability, power, driveability and old skool driving character, yes please.

some people should be a little bit more honest with themselves and just aknowledge that 40 year-old lambda CIS is old junk, plain and simple. it really is. Overcomplicated bandaid engineering.

But i do love the 915 :) :) :) it's mechanical, deliberate, feelsome...and hasn't missed a shift in 4 years, so reliable as well? knock on wood.

Agree if the wrench is as tenacious as some of the guys here.

I don't think there are a lot of efficiency secrets but if you can find a pro wrench that takes it seriously, would be worth the money in a fair "retail" transaction to kill the snake(s).

Please stop confusing us with facts. :D

Yes, they are outdated technology and yes, they are designed by Rube Goldberg. However, I have driven upwards of a million miles on various CIS cars and have yet to encounter a problem. The start up immediately and drive always as if they are warmed up. The only real drawback is the throttle response problem, which cannot be fixed while retaining the CIS system.

maybe they are getting to that age now that everything starts failing or wearing? I'm sure they were very reliable when new. :)

i'm sure there are many SC's out there which would easily take 5k USD to get all their CIS components back to spec. :)

and it's not easy to DIY. You gotta be adament. It's a lot more difficult than just opening something up, cleaning it, and putting it back together (have fun with the FD!) . Spend days and weeks reading up on jetronic, studying like in school, geting hernia from working on the 3 million fuel lines and the unreachable rear AAR bolt, nevermind taking off the A/C and blower motor for the 20th time :D:D

so yeah, better be prepared.

What range would a tenacious P-shop charge to just sort the entire CIS thing out?

A mechanic addresses the symptoms to find a root cause.

However, a wild ass guess is 16 hours to remove CIS and bench test parts and eradicate ALL vacuum leaks and reinstall/dial in. That is if this procedure is your mission and you absolutely know what you are doing and know where all of your testing equipment is.

At $120 per hour, $1,920.

Plus parts.

Working on the CIS would've been so much easier had the components been placed in the front.

No sane mechanic would offer to do the above without dropping the engine, turning a possibly simple fix to major work, costwise.

Dropping the engine or not. No one would do it.

It's not the way you repair things.

The price would be all over the place depending on parts needed. I bet if the system was in total disarray and needed all the seals, gaskets, hoses and airbox replaced along with rebuilding the WUR and FD it could end up around $5,000 parts and labor.

I would think a decent mechanic who knows CIS could do fuel pressures and smoke test the system in a couple hours and at that point could narrow down problems and start repairs.

THE SKY IS FALLING! Hundreds of thousands of SCs are out there running just fine.

When I transferred the CIS parts from my wrecked '83 into my '78, the system had about 350K miles. I have since driven another 60K miles. Similar mileage when I sold my '84 Rabbit (the odometer was broken, but showing 375K miles). No problems whatsoever. Both cars started within the first engine revolution and drove fine, hot or cold.

The sky......is not falling.

iv had my car 13 years and only problems were when i first got it the accumulator was bad so hard hot starts. And it had some backfiring at startup so i installed a popoff valve. Did a smoke test and didnt see anything leaking. A while later i learned enough that i decided to richen up the mixture a click or two and that solved the issue and no problems after that. Any other maintinence has just been replacing old hoses and such. Also had to rebuild the charcoal canister because i had the turds getting in the system.

Your first post is flawed “Avoid carbs. Carbs bad” wrong, carbs are awesome. I’m switching from cis to carbs in the spring.