CIS problems...........yet another thread
 

Background:

Car is an '82SC. Recently backdated the exhaust. SSIs, and MB911 muffler.

Recent (2 weeks ago) valve adjustment, and oil change by factory trained mechanic.

WUR replaced less than 2 months ago (old one was faulty). Pressures within specs too.

Less than 10,000 km on the following:

-Spark plugs (Bosch W5DC)
-Magnecore spark plug wires
-Rotor, and distributor cap
-Air filter
-Fuel filter


Ignition timing set to factory specs.

Problems:

Car had VERY bad exhaust backfiring after the SSI install on deceleration. Tracked down an exhaust leak and this seemed to reduce it slightly. I found that by disconnecting the vacuum retard on the distributor the backfiring was almost completely eliminated on deceleration (very slight now).

There is still a slight exhaust "chuff.......chuff" kind of muffled backfire/miss at idle. Too rich? Idle not as smooth as it could be. Seems to get a little worse once warmed up.

Also, after warmup the idle will sometimes come up about 400 rpm (to 1400) and stay there. Idles at 1000 normally.......doesn't start off high and decrease like it should. After sitting for an hour or so when hot, if the car is restarted it will idle very poorly and at a very low rpm (~500 or so). Will easily rev, and seems to drive okay. Never any problems starting the car......fires right up whether hot or cold.

The other thing is that the car doesn't really seem that much quicker after the install. Sounds great, and it revs much better, but.................

Does this sound like the mixture is causing my problems? I've tried to adjust it and seemed to have some success, but I can;t be sure.

Ideas?

Kirk

Anyone?

Surely someone has some suggestions???

I suggest EFI.

I've been lucky that I haven't had any real CIS issues. But once they pop up, I won't let myself get nickeled and dimed with piecemeal fixes. I'll go EFI and eBay off my CIS.

Take it to a pro and pay an hour of labor to have it tracked down and save yourself 10 hrs. of poking around.

Problem is finding a pro who will actually take only an hour to diagnose it! My past experience with several mechanics (Bosch "certified" too) was that every CIS problem seems to require a new fuel distributor!! Time to look at it myself. Sometimes the 10 hours of poking around isn't so bad.

Kirk

If a 2.7 CIS fuel dist. will fit, I can get one for you cheap.

My FD is fine..........its the mechanics that need replacing.

OK, I'm no CIS expert but I'll give this a shot. It sounds like you have a fuel leak somewhere in the system. Could be cold start valve or injector. Also could be a vacuum leak in the system. According to the Porsche repair manual rough idle when warm can be caused by the following: control pressure to high or low, vacuum leak, entire system leak, pneumatic valve leak, cold start valve leak, defective injector, basic adjustment (idle) to rich or lean, dirty fuel system. Hope that helps.

How did you adjust the mixture? Did you check the WUR pressures first?

Jerry Kroeger

kirk,
don't tell them to look for problems..just tell them matter of factly that you want the mixture set..period. it's always a good idea to get it properly 'baselined' once you get to a point, like now, where you're not absolutely sure that it's correct. save yourself the worry and doubts and get this one parameter ironed out..it may indeed solve your problem and give you peace of mind that your mixture 'is right'.
ryan

Done a fair bit of tinkering with my 911 and my brother's 930, it can make quite a bit of difference if the CO mixture is not right or any of the CIS components are not functioning properly.

Hard to diagnose without knowing all the components are good.

If you install SSI's then you will require a slightly richer mixture to match the increase in airflow, best if you have a CO meter if not can still be done (see posts).

The AAR is what brings the revs up when starting the car, even if it is fairly warm (not fully) it will bump the idle up by passing more air.

Drivability when warm (after CO adj properly) will depend on the proper functioning of the WUR/Dist/inj. Also what state of tune is it in?

Cliff

P.S. Hey bro...how.s the 930, still running hard?

Some SC experts here too.

http://www.dorkiphus.com/porsche/forumdisplay.php?f=41

There has been a lot of information posted on CIS. If you are going to own a car with CIS, you should a least read up on some of the components and learn how they work (not meant to be directed at Kirk in particular).

CIS gets a bad rep because folks don't understand it. They then start fiddling around and get the system out of wack, then they start posting...with all kinds of sympthoms...

Imagine going into the doctor's office and telling him/her your body hurts and something doesn't seem to function right....and when he/she asks you what part of your body hurts and what's not functioning correctly, you say "I just don't know, but I wake up in the morning and I feel funny." Now imagine doing that over the phone or on a BBS.

Kirk has down a good job of outlining the history of his problem, and it sounds like a simple mixture and idle speed adjustment.

If you don't know how to do the field test for rich or lean, search it. If you don't know how the air bypass screw works..search it.

I could tell you, but I'd rather you read it and learn it. Once you read about them, post questions.

My Calculus teacher in HS loved to use the phrase "give a man a fish you feed him for a day, teach a man to fish and you feed him for a lifetime."

I have two books on diagnosing Bosch FI problems, the pressures are within specs. I adjusted the mixture while the car was running and ended up richening until it ran better (small adjustment ~ 1/2 turn). I wish I had a gastester to set the mixture.

Dyno run?

You don't need a dyno! Try the idle screw on the throttle body. Remember, changing air...you must also change fuel.

I just read this in my Porsche manual:

Problem: Speed remains too high at high temperatures or no speed increase on cold engine.

Possible cause: Auxiliary air regulator or auxiliary air valve defective.

Remedy: 1. Disconnect top control line at auxiliary air valve and plug.
Problem corrected: replace auxiliary air valve.
Problem unchanged: Auxiliary air valve good.

Remedy 2: Cold engine: If there is no increase in speed, auxiliary air regulator is defective. Warm engine: Disconnect one hose at auxiliary air regulator and plug both openings. If speed is too high, auxiliary air valve defective. If speed drops, auxiliary air regulator defective.

This is listed for a 1976 model, but I think it applies to other years.

Souk,

I've spent a LOT of time reading on this forum, and reading my two FI books, and the Haynes manual I have (I know get a Bentley manual).

I know how to adjust the mixture and idle speed. The WUR is new, and I adjusted the pin by knocking it in slightly to get pressures exactly as specified.

Car starts beautifully - one quick twist of key and it fires every time. I think it's mixture related...........but looking for other possibilities.

dmarv

I will check what you have mentioned. Sounds like part of the problem.

kirk,
there's simply no way to set mixture/co precisely without a gas analyzer..if you don't buy one, as they are expensive, i stand by the recommendation to have a shop set it. souk's recommendation is solid too..there's a buttload of info on cis problems and realizing that you already have probably enough background and experience yourself from your aforementioned efforts..i'd bet that short of having the shop check it out..your familiarity and experience with your car makes YOU the best research resource..better than all of us shotgunning.
ryan

Goodluck, hope you find the problem!! CIS can be very temperamental!! It takes time to hunt down a problem or two. With the right tools, info, and beer a problem can be hunted down.