crusing problem 76 911s

[mikeyb6s4]

I just picked up a 76 911s and I noticed that a similar post about this problem was stated before on a 83 911? I am noticing the same issues and am trying to resolve the problem. Replaced the plugs and air filter. They were both suffering from age. They both made a noticeable difference, but the same studder is still there around 3000 rpm. I noticed the other thread talking about spark plug wires. They are all in good shape. The distributor cap is new, the coil and ignition box look original. What do you guys think? Im stumped. It does smell a little like it runs rich, but I'm really not sure. BTW, the smog guy was mentioning a misfire and it barely passed if that helps at all. Thank you.

[ossiblue]

Welcome to the forum, and get ready to post some pics of your new car!
I always suggest to new owners of CIS cars to search out an expert mechanic who knows the CIS system like the back of their hand to tune, adjust, and repair the ignition and CIS systems so there is a base line from which to deviate.

From what you describe, the problem could be fuel system (rich "smell") or electrical ("misfire"), or a combination of both. Try to get all the variables reduced by focusing on one area at a time. In your case, maybe troubleshoot the electrical first as it tends to be a bit simpler than the CIS. Once the electrical system is in specs (as well as valves), and if you still have the symptoms, then go after the CIS--lots of expert advice here to help. Bottom line, do one thing at a time and if you are going to DIY, report back here often with anything you find, and ask any and all questions. Could turn out to be something very simple.

[afterburn 549]

If it is missing and juddering under load (not just light throttle I would suspect any and all the secondary (everything from the coil, plugs, wires, cap ,rotor ) these all breakdown over time and voltage will take the ez path to GRD. It does not like to jump a gap, or will choose a smaller one if allowed

[4sd911]

CIS is known for a stumble between 2500 & 3000 rpm's, This is noted in different magazines tech article's, it can be lessened up raising the co level, but that is illegal and a shop can not to that. Of course keep that car well tuned will alway help.

[afterburn 549]

Originally Posted by 4sd911

CIS is known for a stumble between 2500 & 3000 rpm's, This is noted in different magazines tech article's, it can be lessened up raising the co level, but that is illegal and a shop can not to that. Of course keep that car well tuned will alway help.

No Offence..never herd of that..do not know why that would happen as the flapper valve is almost linear @ all positions (fuel delivery )

[Paulporsche]

Welcome.

You should avail yourself of the search function, although it sounds like you may already have, as you are aware of the other thread you mentioned. There is a ton of info from knowledgeable people re the CIS.

As a general rule of thumb, it is best to always start w/ the ignition components. Looks like you've done this, except I didn't see you mention points. The point gap isn't as critical in your car as in earlier years, but it is still important to get at least close to spec. Bad points can cause start and run problems.

So next you want to move on to looking for vacuum leaks. These are very common in CIS cars and can be troublesome to track down.

AFA the FI itself, do what others have said: check your fuel and control pressures w/ a fuel pressure gauge, and your air/fuel mixture. Since the car is new to you, it's good to have it set up correctly to begin with. If you don't want to do this, a shop should be able to do it fairly reasonably. The mixture and the functioning of the Warmup Regulator (WUR) are critical to getting CIS cars to run smoothly.

[longhornchris04]

Mine used to have an intermittent stumble in that range (79 3.0 transplant). I had a full tune-up (valve adjust, plugs, cap, timing, CIS adjust, etc) and haven't had a problem since. I debated DIY but I don't currently have the time, tools, or space.

This was the first tune-up I had done. PO had the car in decent shape when I bought it (PPI didn't say indicate it was out of tune), but the performance below 4k improved dramatically post tune-up. If I had to do it over again, I would have done the tune-up first.

This is a subject, change, but since your car is "new to you," and a 76, does it have the reliability mods. Specifically:
- 11 blade fan (painfully obvious)
- CIS pop-off valve - remove the air filter, should be a big valve on the left side of the box.
- Carrera Tensioners - on the rear chain-covers you should have small oil lines leading into them
- Thermal reactors scrapped - they are terrible for the engine (doubly so for the mag cases) and don't do that much for emissions, especially with the 11 blade fan.

If it was rebuilt, have the valve guides been replaced and the case reinforced against pulled studs (case-savers). How many miles, general background info.

Also, where are you... are emissions a concern (you mentioned them, is it tail sniffer or inspection)? If so, a mechanic may tune your car for emissions, in which case you may want to tweak it after you've gotten your sticker. Ok, so its cheating but emissions controls are what causes so many mid-year porsches (75-77) to die young. There are some threads about tweaking to pass the sniffer then adjusting back for performance/protection.

Oh, (I was guilty of this too so don't feel bad) Post some pictures, and welcome to the club.