1978 SC - Fix CIS or change to different injection, carbs, ITB etc?
 

Hi! I am getting a bit sick of fiddling and shotgunning which parts to replace on my CIS and ignition system to make my 1978 SC run as smoothly as I would like it to. I have indications that the fuel distributor might be worn out, but I'm still not sure.

The problem is that the car is running bad while cruising around 2000 rpms. If cruising at 1500 its better, and its also good while accellerating with some pressure on the pedal.

This has been done:

"New" distributor (Tried three...).
New signal cable to distributor.
New coil and plug cables.
New WUR.
New fuel pressure accumulator.
New fuel injectors.
Adjusted and serviced by experts.

I am now considering what way to go to make the problems go away permanently. I have been looking into a tec-gt kit with a 3.2 intake. Also considering carbs/ITB's, combined with computer management. Another option is to keep changing the CIS-parts.

Does anyone have any recommendations on what to do?

Criterias are that it should not make the car less drivable, since I use the car as a daily driver in the summer. It should also not limit future improvements to the engine, if I decide to take it apart and make some modifications in the future.

Any input appreciated :)

at least consider the bitz racing kit (bitzracing.com). i bought mine NIB from a seller who went in a different direction (paid $1200). the kit is easy to install. almost ready to run it. here are most recent pics (2 days ago)...http://forums.pelicanparts.com/porsche-911-technical-forum/595520-my-911-sc-minor-overhaul-3.html

Thanks for the tip! I have been looking at the bitz kit. However I have read some posts about people getting really poor effect with it on dynos and going back to CIS. This might have to do with tuning though, so it would be interesting to know how your engine will perform when its complete.

Anyone else have experience with the bitz kit, good or bad? Anything outside of what's included in the kit that is necessary for best performance?

Talk to JP Novack about the Bitz kit. You can source a good set of 40mm Webers for around $1500. Your car will be totally different with better throttle response and better power. You'll give up a little economy but not as much as many claim. Carbs are simple, easy to tune and bullet proof.

If you do go carbs you'll need to send your distributor out for re-curving. You will not believe the difference the carbs will make in the overall performance and feel of your car.

Lindy

What about drivability on a daily basis, and how does the car run on cold mornings? Spring and fall here in Norway can be down towards freezing, but I would still like the car to function without needing to warm up too much before taking off.

My CIS is also not in the best shape, although it runs good enough when warm, so I'm also thinking about an upgrade. If/when I do it I will probably go for PMO ITBs and the megasqurit EFI.

It a bit on the expensive side but I'm thinking that some of it can be recovered by selling off the CIS parts (some of them should be ok) as they are getting more scarce and sought after. You have a few new parts that should bring in a bit of cash from what I read.

Cheers, Björn

Do you have emissions testing where you live?

I think your first problem is that your are not allowing the engine to run in it's optimum rpm range. You should never drive with it below 2700 rpm. Typical street drivin should range from 2700 to 4000 rpms with occasional spikes to red line. These engiens are intened to be reved, they are not 'merican V-8's.

When you drive with a bit of spirit, does it run better?

I read the original post this morning, and have been waiting for someone else to ask these questions, but on one has.

Are you working on the car yourself? Or has a mechanic been trying to diagnose?
Do you have fuel system pressure testing equipment? What are your fuel pressures? Lots of info here on CIS troubleshooting.

Have you checked your distributor advance to ensure it is working correctly?

If you want to maintain drivability, you may not like carbs on cold mornings. My CIS works great and I have kept it because I drive the car in all kinds of weather, and it starts right up and runs great all the time.

Scott: No emissions tests for my car here :-)

HarryD: Good point about driving with more spirit. Maybe I am expecting it to behave more "modern" than it is made for. It's of course a lot more fun when keeping the revs up a bit, and it does run quite well when give it some more to work on. But it is just strange that it behaves well all the way from 1200-1500 while accellerating, but when cruising between 2000-2200 it behaves bad, and again cruising or accellerating further up is fine.

Walter: The car has been diagnosed a lot by different Porsche mechanics, and also by a Bosch specific shop. But they are not able to pinpoint the problems, but it seems fixing one thing always leads to another, and i would not want the loop to start over after changing everything. Fuel pressure has not been checked though, but I recently got the meter kit so will test it.

I had PMO on my 3.0 SC and they were great. I would recommend them over webbers.

If you're describing a hesitation under accel. it could be as simple as sensor plate adj., to as bad as fuel dist. plunger sticking. Seems like alot of people have been guessing with your money. Bummer. If you want to DIY, this site's a great place to be. Get the Bentley manual from our host start searching and asking questions. Not into wrenching, post your location and get some good references to good shops.
Lets start with a liitle CIS process of elimination. how's it start cold/ warm? any other symptoms or issues? Has this always been the same issue,or is it "evolving with new parts"?

I've seen PMOs that work well and I've seen Webers that works well; it's all about what you can find and how much. The carbs do take a little bit to warm up but nothing extraordinary. For the money they are hard to beat and once they're set up your done.

I spent huge amounts of coin (and I mean huge) and time trying to get my CIS running right, using various experts and replacing most of the system - all to no avail.

I have just completed fitting a set of PMO carbs and will get to use them for the first time this weekend.

I'll post the installation experience and first drive impressions as soon as possible for you.

If you don't understand an out of date injection system, have the right diagnostic tools and parts....it's a waste of time and YOUR money.

Carbs on an engine with FI cams is also a waste of time. RTFB.....

Why not sell your 3.0 and put it towards a 3.2? Might be more cost effective.

Carbs does not tempt due to cold driving conditions. A swap to a 3.2 is not very tempting either, and I can't really explain why. To me it just feels more right to modify the original engine then to swap. Also a swap risks getting a 3.2 that needs work too.

The only issue I have at the moment is that the car is running rough while cruising. And by cruising I mean 4th or 5th gear at 50-60-70 mph, steady speed. Accelerating is fine. I can go from 1000 rpms to redline with the pedal to the floor in f.ex. 2nd or 3rd, and (to me) it runs fine through the whole register. And since I am a bit tired of trying to fix this (small) issue, I am considering the options, but I won't compromise on driveability after a cold start or in heavy traffic etc, where a CIS car behaves very well.

My original question was more related to what options people recommend than to try to fix this problem, as I have been fiddling with the problem for 3 years. Every little thing I have tried have led to another problem, sometimes due to wrong diagnosis, so now it's back to excactly how it was 3 years ago after (unneccesary) having worked through all the items I listed as done in my original post.

At the moment I am waiting to hear how this car is running after converting with the Bitz efi kit:

http://forums.pelicanparts.com/porsche-911-technical-forum/496861-should-i-go-digital-wur-bitz-efi.html

This engine is done by a fellow Norwegian. I know about some of the pros and cons on this kit already, but if anyone has first hand experience with either positive or negative results I would be interested in hearing about them.

With the investment you have in so far, why not source a complete working CIS system and swap it in for a test? At least that way you could help eliminate external factors.

Have you sprayed carb cleaner at the base of your manifolds for vacuum leaks?

Even if it were zero outside, the time to warm the engine with carbs is going to be minimal. They have an accelerator pump that is manipulated by way of your right foot. Three pumps of the pedal, turn the key and viola, she starts right up. Yes you'll need to let it warm up a little but that's true with any induction system.

As far as carbs and cams; everything is a compromise. No matter what you have there is always something better. Are SC cams perfect for carbs? NO. But a motor that runs decent with carbs is a lot better than a motor with CIS that doesn't.

Cfeste,

There are several things that need to be checked but you need a fuel pressure test gauge to do it. First thing I would check to see if your fuel pump has an "inlet" filter on it. If it is a newer fuel pump, it probably does.

Next I would check your fuel pressure to see if it is within specs - cold and hot. Another item to check is the fuel pressure regulator. In addition to that there is a check valve on the back of the fuel distributor that regulates pressure back to the fuel tank

Also check the fuel filter next to the accumulator. It could be partially blocked. Pull your injectors out and do a pressure test on them. It's easy to do -

You will definitely need a fuel pressure test gauge to check the fuel system out properly.

SteveKJR

"A Porsche does more then just go fast in a straight line "

did i miss air leaks as the issue?

injector sleeves, Orings, intake runner boots, intake gaskets, all the AAV and AAR plumbing inthe back. all potential air leaks. and dont forget the vent system to and from the oil tank, along with the oil cap.

control pressures

compare all 6 injectors for fuel volume at part idle and WOT. if that is good, your FD should be good.


dist- i see you have had 3. correct dist? is the advance working? vacuum advance/retard working?

you get all that straight, and it should be fine.
have you done any engine mods?

carbs- i love the sound, but they are a lot more envolved than CIS. CIS has 1 adjustment, carbs have 13+ mechanical adjustments, not to mention jets, and tube selection.

i suspected my fuel dist for a long time. something kept telling to keep looking. i found a clogged injector line.

im not a big fan of CIS after having it on lots of other cars. i am in the process of installing standalone EFI into my SC using an 3.2 intake manifold and lots of other non Porsche parts.

I have ordered the Bitz kit, and looking forward to installing it :-) Will post updates in a few weeks!

Had similar issue with my 81sc. Pulls strong through all gears to redline, but cruising would cause a slight jerky feel. Now I know that the backlash is coming, but I simply disconnected the O2 sensor (after much reading on this forum) and the car runs great! If you are still running a cat I would not recommend, but if not, give it a try.

Cis
 

Talk to Larry at CIS Flow Tech . He's the man !!!! SmileWavy Larry just finished rebuilding my fuel distributer & WUR . W O W :eek: The Car runs Perfect now . Nice & smooth then Roars. CIS is not so bad !!!!!:p

Best of both worlds is the PMO ITB's. Modern FI with that great carb sound and look.