CIS Help

[tstan]

My 78SC CIS is giving me headaches. After taking it to 4 different shops (without success), I'm determined to find the problem myself if need be. I already have a Bosch Fuel Injection & Engine Management book. Very good for overall theory, but does anyone know of any other publications that might help me get more specific to this car?

[wckrause]

The Bentley manual has some good stuff on CIS.

What are the problems that you are having?

I had a similar experience with mechanics working on my CIS. They just liked to swap parts and charge me money. They never were able to fix my cold start problem. With the help of this board, the Probst book, a CIS pressure tester and the Haynes manual (yes I said Haynes), I was able to solve my problem.

[tstan]

Boy you hit the nail on the head. I've had shops tell me everything from "I can fix you up with just a tune up" to "well, you know the car IS 24 years old".
My problem is when the outside temp is above 82 degrees (when it's colder the problem goes away), and the car has been sitting for 8hrs +, on start up the rpm's drop to almost stall then after sputtering for +-10 seconds it returns to idle. Then all the way through warm up it stalls when you push in the clutch. This has plegged me for 3 years and now I'm affraid that there may be other worn out componants that might be adding to the problem, hence the request for better reading material. I have 215000 miles on her and over the three years and 4 shop visits the WUR has been replaced twice, the decel and aux air valves have been replaced, and I replaced all the hoses when I pulled the engine to replace the head studs. Any ideas would be greatly appreciated.

[wckrause]

That sounds like a tough one. Have you or your mechanics looked at the ignition timing/distributor any?

The 78 and 79 SC's (and all of the ROW's) have the K-basic CIS system. They also have a seperate vacuum limiter and aux air valve. Maybe you have a problem with the vacuum limiter (also called the deceleration valve). Another often overlooked component is the thermovalve. It isn't even mentioned in the Probst FI book, or in the Bentley manual, but it is included in a vacuum diagram in the Haynes manual.

You should do a search on "deceleration valve" or "thermovalve" to see some previous threads. The thermovalve is involved in cold starts, and the deceleration valve will effect idle speed, but it seems to cause high idle problems.

If you're planning on working on your CIS, you really need to get a CIS pressure tester. You can get one at JCWhitney.com for about $60.

[tstan]

Well it's funny you mention the distributor. I just pulled mine yesterday to replace it. Don't know where I might pick one up do you? Porsche wants $800+.
I've replaced the thermo valve and replaced and tried adjusting the decel valve. I have the CIS tester. The last time I ran a check, it was in spec. That has been some two years ago. I think what I might do is wait for the warm weather to return to Ga., forget everything the mechanics and I have done, and start from scratch. Before I did that I wanted to read up on as much literature as I can get my hands on. I have a Haynes book, never thought of blowing the dust off it, but I'll try it too. Thanks for the ideas!

[john70t]

Those mysterious mysteries seem all too common with CIS.

Just from the words "It stalls when you push in the clutch" I thought to bring up the idea of the throwout bearing. If the engine is weak by other factors mabye its putting too much of a drag on it. Just an idea.

I had a friend with an old 320i whose emmisions would burn super clean for about 10 minutes and then top the charts. A glowing orange cat indicated it was dumping fuel (and probably needed a new cat) and seemed to mystify all the people who looked at. Injectors wern't leaking but he couldn't test the fuel pressure.
After several months of frustration he finally threw parts at it: replacing the O2 sensor, the frequency valve and the regulator which seemed to fix the mixture inconsistency but still didn't bring it into specs. I think it had 1.0-2.0% CO after the cat (not outrageous for a bad cat) but still had about 400 HC.
A cat is usually good for about 400ppm HC and 2%CO(unless its a Ford cheapo) and his engine has 250k miles so it almost seems within specs.

[Hladun]

Some thoughts;

The thermotime switch (thermo valve) only (repeat only) works when the starter is engaged. The only other failure is that it can leak, this causes the car to run too rich. This doesn't sound like your problem. If your car starts, forget the thermotime switch.

As a first step, increase your idle speed to about 1100 rpm and see if that helps.

The deceleration valve, (useless) auxiliary air valve and auxiliary air regulator usually cause the engine to run above idle speed or surge.

Tstan, you say it stalls when you push in the clutch. That's when you unload the engine? It could be the deceleration valve. When your engine is warm and you take your foot off the accelerator the rpms should drop to about 1500, hold for a moment and then drop to 1000. If this isn't happening your deceleration valve may not be working properly (it is adjustable).

The last part of the CIS system is the fuel side. The Bosch Fuel Injection publication gives the procedure to test the system, control and rest pressures. I'd do a comprehensive system pressure test. I suspect the system is running too lean to allow your car to run when it is cold (but the WUR is quite warm giving a high control pressure). Also, is your CO properly adjusted. (Set it on the rich side, high CO).

The ignition system might also be a possibility, but I have no theories here.

[Superman]

So let me get this straight. You've replaced several expensive CIS parts without solving the problem and now you're going to spend $800 on a new distributor. I took my distributor apart while my engine was in pieces and the only benefit was I leanred now tot ake it apart and put it back together. It needed nothing. Bushings were tight and everything clean and free-wheeling at 182K miles.

surging suggests a rich mixture. Next time this is about to happen, open the deck lid and take off the air cleaner and cover. Start the car and then go to the engine. See if gently pulling down on the curved part of the control lever helps smooth out the engine. Perhaps goose the throttle and try to make it lag and die. See if you can make it avoid the dying part. If things get smoother while you pull down on the lever, the mixture is too rich. If they get smoother by pushing the lever up, then the mixture is too lean.

I would say a lean or rich mixture alone can do this, if it is out of adjustment. It is certainly fuel pressures you are talking about when the engine is too rich or lean, either warmed up or cold. So you will need a pressure tester.

[john70t]

Hey Superman et all, do the CIS 911s use the same clear plastic snap-fit hose as some of the bimmers?
Are there any special techniques/tools for safe disconnection besides cutting off a small section and reconnecting?
It does sound like it's too rich at idle but what about the clutch effect? Dirty throttle plate? Is there an idle bypass screw?

[wckrause]

Hladun --

The thermotime switch and the thermovalve are completely different parts. Your description of the thermotime switch is however, very accurate.

The thermovalve, is a small plastic disc that connects to one side of the WUR. It is only used on 78 and 79 US models, and on ROW models.

It is part # 17A in this picture

http://www.pelicanparts.com/911/911_Parts/1978-83/1-7-2.JPG


I think the SC's went to steel fuel lines in 1980. You don't have to cut them to disconnect them. They press onto either a threaded fitting, or a banjo bolt.