CIS mid range issues
 

Greetings,

Got my 2.7L 1977 911 Running after the rust repairs and am having some mid-range acceleration issues.

I have just started researching the CIS system and haven't found a solution to my little issue.

First and foremost I haven't done much to it yet in the way of taking it apart and cleaning / inspecting so don't hate me for asking, but I will tell what it's doing in hopes of someone giving me some suggestions.

1) it starts up just fine. Goes to high idle and warms up correctly.

2) once warm the idle is a "little" rough at about 900 rpms.

3) When accelerating the car is hesitant (seems like lean mixture) in the midrange (2500-4500 rpms) on light loads.

4) Car accelerates VERY well when you mash the throttle 100%. Its just the transitions in mid range throttle that get it coughing.

My assumptions are that I'm going to have some air leaks in the system. I'm also going to clean / lubricate some of the parts while I'm at it.

Timing is on, new ignition system.

Thanks,
Patrick

After you check for your ignition system and search for leaks you will need to check your control and system pressures, do system internal leak check. Here is a bunch of good info on cis systems:
CIS Primer for the Porsche 911
You will also need the pressure/temp chart for your year car, you might also verify that you have the correct WUR on it. If you do a search on setting the mixture you will find out how to do it. I think you need an exhaust pipe meter to check it properly, but there are plenty of threads about how to guesstimate it.
You might check that your injectors spray properly. If you get leaks around the injectors where they go into the intake tubes there is a good possibility that the o rings around the plastic sleeves are bad, not just the o rings on the injectors. If you search you will find plenty of info on that.
Good luck.

Welcome, Patrick. May I suggest you add your car's year and model to your signature or screen name so, in the future, others will be able to offer more specific help.

Ray_G has given you the basics and I agree, you seem to have a lean condition. CIS can drive you crazy if you don't proceed in a step-by-step way to track down issues. You have already eliminated the ignition as a problem, so the CIS is left to be dealt with.

My suggestion with CIS is to eliminate the easy things first, in this case, start with fuel pressure checks as mentioned by Ray_G. You will need the chart mentioned for cold controlled pressures. If the pressures are in spec for your car, next is tracking down air leaks, and this is where knowledge of your year engine is important as there are several changes/additions in CIS components over the years which can account for leaks.

Post your car information, do a system check of fuel pressures, and let us know what you find.

Thanks!
 

Thanks for the replies so far. I'm reading the primer and testing my new signature.

Wow
 

Ok so I got to working on this thing last night and found a bit of an issue.

Someone has been here before me and to my surprise they changed lots of parts. BUT, they did NOT change the large rubber "Y" hose that is part of the Aux air system. It was cracked in two places. Then to my dismay it's a $180.50 part! Yikes, I think I'm going to try to build my own out of some hoses and a Tee. Might have to loop around and be careful that it doesn't block anything, but It should do the trick as far as fixing my air leak. Seems to make sense that it could have been the problem.

It was such a pain to get to that I decided to pull the whole setup. Then I decided to pull the alternator and fan as well as the shroud and clean up everything. Someone DEFINITELY just went through the heads at least because the cam towers are CLEAN. Is there a way to tell if the case has had Case Savers installed?

Patrick

Glad you found your leak. As for the case savers, well they are at the bottom of the head studs in the case obviously, and the cooling tin makes it hard to see in there - let alone if they are done. Even if you can see an insert you still won't know if they are case savers, or timeserts. And some even used helicoils. You would have to completely disassemble the case to have case savers put in. I guess if the rest has not been taken apart I doubt case savers are installed. If you do a search there is all kinds of information about the different inserts. But I think pretty much everyone agrees that case savers are the way to go.

Reason I ask
 

I have 3 receipts that came with the car:

1) is a handwritten list NOT in receipt style...like someone talking to a guy at a shop would have written down on what needed to be done and has a breakdown of hours for each task. It indicates several things including R&R heads and to "install threaded inserts".

2) I have a PARTIAL real receipt and rather inconveniently where it says THREAD INSERTS, the quantity portion is torn off. So I don't know how many they did...damn the bad luck.

3) I have another receipt detailing lots of ignition work as well as the "timing chain gears", "the pressure fed tensioners, etc on it.

I will make a list and see what you guys think. I will take a better look at them today.

Best news is one of the receipts is dated at 110k miles...and the other looks like 2005 (last inspection sticker as well) the car is at 112.5k now. The original owner died and a second guy bought it and it sat for years. Then I bought it and saved it...so I'm just trying to figure out what I have.

Intake valves and cylinders look GOOD inside!

Thanks for the input so far.

patrick

If the receipt says R & R heads to put inserts in then they are not case savers. It is my understanding that you need to have a mill to do them. I bet they put timeserts in. Just a guess on my part though. I don't think I would worry too much about it now. I would just torque the heads every valve clearance check and live with them for now. When I rebuilt my 2.7 I did not have any pulled studs at all, at 163k on it. the bottom end needed to be gone through and the heads were trashed. I did have the case savers installed with all the other machine work. Once the case savers are installed they have to machine the spigots because when they install the case savers they expand the case as the install them pushing some material into the spigot for the cylinder. At least that is my understanding. Anyway that is the work done on mine, I don't know how you could do that without taking the case apart and putting it on a mill.