CIS Problem

[DohertyCM]

We used a smoke machine to find all of the air leaks on my 2.7 (CIS) with a 964 cam. We fixed them and now I have an occillation when its starts and when its warm. I was told the car was lean so when I turn the adjustment screw clockwise the car will not idle...when I turned it counterclockwise the car idled and smothed out.....seems obvious i did something right...maybe..

But my question is does anyone have a picture on where i can hook up a dwell meter and how to do it so I can check with a meter...?

Is there a thing as too lean? too rich? that would hurt the car?

or should I not really worry about it and continue to use the VW type tuning method....my ears...

Need to get this fixed.....Got Road Atlanta event this weekend for the first time....

[Walter_Middie]

DohertyCM,

This seems like a text book example of what happens you get air leaks developing over time. The engine is richened by the owner to compensate for the extra air getting in. When you finally fix the air leaks, then the car is running too rich, and the idle will hunt up and down. You did the right thing by leaning out the mixture.

You don't want to get it too lean. This will raise your engine temps - especially at the exhaust valve. A lean engine, run on the track, is a recipe for disaster. This is what happens to turbo cars - and also to a NA car like yours - but not as serious, or as sudden. If I were going to take my car to a track and run it hard, I'd want my mixture set correctly - not just by ear.

[Vin-barrett]

Curious as to where you hooked up the smoke machine to the intake.
I want to do the same thing with my CIS car

Thanks
Vinny

[DohertyCM]

Neat machine they had. They hooked up to the exhaust to find leaks coming from that end.

Then they hooked up to the intake with the plate propped open and went through that way as well.

And when they turned the machine on, the car started smoking in all kinds of places!

Fixed them all and now this idle problem popped up.


I still would like to see some pictures of where you would hook up the dwell meter and detailed instructions on how to do it.

[Walter_Middie]

Some 3.0 L engines had a frequency valve that worked with the exhaust lamda sensor - the frequency valve can be adjusted with a dwell meter - but you don't have a FV.

[Paulporsche]

You have found out that your mixture was probably too rich, not too lean as you were told. An oscilating idle is a common symptom of too rich.

Be careful w/ that adjustment screw. I usually make adjustments about 1/16 0f a turn @ a time, since a full turn represents somewhere between 8 and 12% CO. These engines seem to like it best between 3 and 3.5%

You can search for the "push pull" method of adjusting the mixture w/o a meter, you can have a shop set it once as a baseline, or you can do what I do: set it to where it is just shy of producing the hunting idle. That way you should get max richness, max horsepower, and cooler temps. As you have found out clockwise = richer.

I have been using my version of what you call the VW method to tune my CIS cars for 30 years.

BTW if you have to conform to emission regs, then obviously a meter would be needed.

[JBO]

Rex and Paul are exactly right - if anything you want to be too rich rather than to lean. Too lean you will run hotter and also run the risk of backfires through the airbox. Is it possible to be too rich?? Seriously, if you have a hunting idle or surging /popping out of the exhaust, generally this means you are a rich and turn left a little on the adjustment screw. It sounds like you are now OK with the change you made. If it is sputtering/backfiring through intake when cold then you went to far and need to richen it up a bit. Thanks to Souk and Paul, I have been adjusting mine successfully by ear for years now after having it professionally done with a meter years ago.

[DohertyCM]

I had to turn the screw about 3/4 of a turn to steady the idle. But I will fine tune again this evening and turn to the rich side until it just starts the hunting....

But I will do that just after i put the new headers on!

[DohertyCM]

I have turn the screw back and forth trying to get it adjusted right at cold and hot. And I was at a point where I was fighting myself i thought.

So here is what I got, when its hot and I step on the clutch after driving the car wants to occasionally die when I come to a light
So if I turn it back to the lean side about a 1/4 of a turn the idle will be steddy and wont die during this situation....is this where I want to be?

[Paulporsche]

Since these engines can run @ anywhere between about .5 and 3.5% chances are you are OK. Personally, I would now nudge it back towards rich in1/16 turn increments and see what happens.