CIS Idle Speed and Mixture Setting Without an Analyzer - Page 2

Paulporsche · 10-28-2005, 07:38 PM

Chris,

Re your descriptions: If the revs drop and then swing back up while the car is coming to a stop, your mixture is probably too rich.

If you get a little hesitation when accelerating from a stop, like the engine is kind of "spooling up" before it pulls strongly, then the mixture is probably too lean.

Gunter · Gunter's Garage

Sounds good to me.

wswilburn · 10-29-2005, 08:25 AM

Vash, the 'duty cycle attachment point' is a three pin cylindrical connector located on the left side of the engine bay near the CDI. It is black with a rubber boot covering the connector. There is a pretty bad picture of it on page 240-25 of Bentley. You want to connect the dwell meter to pin 2 (signal) and 3 (ground). My dwell meter reads in degrees, not duty cycle, so I have to convert: 30 deg. = 50% when the meter is set for 6 cylinders. After the engine is warm, you simply set the idle mixture and air bypass so that you get the correct idle speed and 50% duty cycle.

erobinson · 10-29-2005, 06:36 PM

to be honest, not knowing any better, I read what everything did then I just tweaked mine like I would have a Holley carb and it runs well enough with a nice stable idle and starts easily. I think I got very very lucky because all of my components sat on a shelf for six months. The only issue i have is occassionally the WUR is a little cranky after sitting for a couple of days. It really seems like the control pressures are all over the place for a few minutes then everything stabilises and no problems again for a few weeks. I just blame it on 30 year old components and consider it part of the personality of the car.

On the duty cycle thing, my car doesnt have a lambda so I can not try this, but I have a low cost (around 30 bucks) digital multimeter which has a duty cycle function. Something to keep in mind for the guys who want to try that method because you can never have too many dmms :P Plus its an excuse to buy tools which is always good

Again kudos to Souk, always great and informative stuff!

emac · emac's Garage

Scott
I tried the duty cycle port adjustment thing with my dwell meter and did not get any reading with any of the pins. I did set it to 6 cyl. as I read on a post on rennlist but the meter did not regester anything. When I set my Vohm meter to m/amps I do get a reading but have no idea as to what to do. Go so angry I took the dwell meter back and got my money returned.

echrisconnor · echrisconnor's Garage

Souk,

It almost seems CIS need its own section of board; there are so many questions posted. An expanded problem/solution matrix would be great if you ever got around to it.

More telltales:
Popping from intake/airbox (to lean?)
Backfires from exhaust (too rich? or an air leak).
Surging at idle (too rich?)
Runs hot (too lean? can you get high temperatures form being too rich?)
Black smoke from tailpipe (too rich?)
White smoke from tailpipe (too rich?)

These aren't problems my car exhibits, I'm just trying to get a bunch of the telltales I've experienced in the past verified and documented.

howiee · howiee's Garage

Great info, I've been having idle problem for a while so I'll give this a go.

Thanks Souk

MotoSook · 04-18-2006, 07:49 AM

Ahhh...it is that time of the year when minor adjustments will be needed.

I'm glad the stuff I post are helpful. Good luck.

Jim Williams · 04-18-2006, 05:43 PM

Souk,

I've read the initial post in the thread, and I need to raise the question about your statement that the airflow meter doesn't meter air at idle. The air flow meter/ fuel distributor doesn't allow any fuel out the injectors with the pump running, and the plate at rest, engine not yet started. It begins to inject fuel as soon as there is airflow past the sensor plate, so I don't know what else you could call this except for metering fuel at idle.

Also, it's a bit misleading to say that the only way for air to get into the engine is via the throtlle bypass, as all the air that gets into the engine has to come thorugh the air flow sensor (unless there is an air leak). The air that bypasses the throttle has already gone through the airflow sensor. So even with a closed throtlle (at idle), air flow is pushing up the airflow plate.

No intent to be critical, as I know you have a good grasp of the CIS, but I was thinking that someone new to CIS might be mislead by the way this was stated in the post.

diabolos88 · 04-18-2006, 06:32 PM

I know this might be non topic, but if you some of you are having high idle issues, it might not be a too rich condition. In fact it might not even be a AFR issue at all. The culprit could actually be the decel valve. Mine developed a leak from the back hose which was rubbing up against the throttle linkage and had rubbed through. My solution was to just remove and plug the lines. As for the idle mixture, I also have been following these methods Souk has outlined with great results.

Souk, any word on the wheels?

MotoSook · 08:36 PM

You are correct Jim. Air does have to go through the air meter housing to get to the throttle. There is enough differential across the air plate to move the plate just enough to raise the plunger (and break the contact with the switch on the back of the meter housing) in the fuel distributor. Fine adjustment of the plunger height is then performed with the idle adjustment screw.

My state of mind during that initial post was to conclude that the plate-venturi (meter) is not metering, because the plate is still within the throat of the venturi. But that was a poor conclusion on my part. A portion of the plate (furthest from the fulcrum) does clear the throat, teetering on that ragged edge where the differential pressure holds it. The throttle bypass changes the flow rate around the throttle plate at idle, which inturn affects the differential pressure across the air plate (increase flow---increase differential), determining its height. Adjusting the throttle bypass in conjunction with the idle mixture screw achieves acceptable idle mixture and speed.

So yes, it was misleading. I hope the above (and your post) clears it up and prevents anyone from going down a wrong path.

Macel · 06-13-2006, 07:33 PM

Hi all.. Im a complete newbie as far as working on porsches goes... In fact, I don't even own one.. This is a problem with my dad's car..

This topic seems relevant to the problem we're having with my dad's 1984 Targa.. Sorry if I should have posted this elsewhere.

He was experiencing some rough idling and read in a book that you can adjust the idle mixture (I guess that's the one right above the intake box eh?).. Anyway, he had me see if I could find an allen wrench that would fit and eventually I found a 3mm that seemed to be working. He didn't tell me what I was adjusting, so I guess I assumed it wouldnt be something as important as mixture. What concerned me though, was that there was no 'clicking noise' that the book we were reading was explaining we'd hear while turning the allen wrench. We had the engine off while we were doing this. I turned it clockwise a few times and my dad tried to start the car... Started and immediately stalled, and thereafter it would only turn over. So then I guess he went crazy, took a wrench and was turning it with that. I told him I turned it clockwise so he should turn it counter clockwise, but Im not sure if he had the same interpretation of counter clockwise as I did. In any case, it turned it so many times in one direction that now the thing is stuck.

Well, I guess my question is, is there some way I can visually inspect this thing and determine which way I need to back the idle mixture screw out to fix it? Or are we gonna have to order a new part, which I am guessing is gonna be somewhere in the 1000's of dollars since its a Porsche part? He went to bed muttering all sorts of words which shouldn't be said here.

84toy · 06-13-2006, 08:58 PM

If it's an 84, I doubt if it is a CIS system. You might want to post a picture so everyone can confirm what you are working on and the screw you are playing with

Mysterytrain · 06-14-2006, 05:04 AM

As long as this thread has resurfaced..I have noticed that on the Jim Williams CIS site he suggests that when doing the push/pull method one should try for a slight increase in idle speed when the sensor plate is lifted. This seems to make more sense to me then having the rpm's drop. Any thoughts? I'm also wondering if anyone has ever checked the CO of their car after doing this 'rough AFR tuning' to see just where things actually are with this method.

Macel · 06-14-2006, 06:15 AM

Well it seems to me like the idle mixture setting isn't quite as important to fine tune - I'd be more concerned if I were leaning it out too much under higher revs.

Gunter · Gunter's Garage

Macel:
What engine is in this '84?
'84 Carrera has a 3.2 with Motronic: No adjustment possible.
If you were able to insert a 3mm Allen into the Fuel Distributor top to set mixture, it's a 2.7 or 3.0 liter with K-Jetronic.
Without knowing what you were doing, with the engine stopped, why would anybody just "screw" around the adjustment screw until it gets stuck?
Mixture is adjusted with the engine running and only if you know how; very small movements cw or ccw.

Why not get a manual, like the Bentley, read and learn about these engines first before playing mechanic?
To help you out with this, let us know what engine you have; you'll find the number below the fan post on the case like: 930/07

Unless your post is just a joke???

Macel · 06-14-2006, 08:26 AM

No to be honest, I know nothing about porsches and was just giving my dad a hand with this. Since he knows nothing about computers, Im here posing the question for him. I was literally just turning the wrenches he was telling me to turn while he was reading out of some book, so don't look at me!

Had I personally known what I know now about what this adjustment does, I would have certainly been more careful though.

I err, will have to check exactly what engine it is when I get back home tonight.

kach22i · kach22i's Garage

Sounds like you leaned it out too much for starting. Should you get it to start with this same setting you may melt the top of your pistons with extended use.

It's better to run a little too rich than too lean and idle setting too fast rather than too slow.

If it is running way too rich, excessive gas will not combust and will mix with the oil which may ruin the piston rings from lack of lubercation.

There are a bunch of little things which may prevent you from getting a proper mixture and idle setting, the WUR (warm up regulator) is just one of them. I'm in the process of fixing this on my CIS system.

Could be shop time, don't bend over to pick up the soap.

MotoSook · 06-14-2006, 08:51 AM

You stated that you have a 1984 911. If that is the case the engine bay should look similar to this: (Notice the air meter connected to the cone air filter)

MotoSook · 09:02 AM

If you have a 1984 but it has the CIS induction (I'm trying to find a picture of an engine bay), then someone swapped a 3.0 liter into the car which should have a 3.2 liter engine similar to the one I posted in the previous post).

I have never heard an idle mixture screw click. What ever book you and your dad are reading, put it down. (There is no one book that I have come across which puts all of CIS's concerns between its cover. So don't assume that book is the end all be all).

Where are you? Maybe there is someone near you that can come give a hand. Don't be offended, but the skill level I sense of you and dad is not up to adjusting CIS. If you keep going forward you will end up costing yourselves a lot of time and money...