Rich/lean mixture test question or explanation

[mike sampsel]

I’ve seen a reference to a simple lean/rich test of mixture for CIS herein. Having trouble finding an explanation of it.

If car is idling and one pushes the sensor plate up slightly and the car stalls/dies this means what? Maybe a better question:
is this test and the results defined somewhere?

[Flat6pac]

Giving it too much fuel and the throttle opening is closed so it’s a stall situation
Call me this evening and I’ll explain it to you
Bruce

[SkiVT]

This link may also help.

911 CIS Primer - Testing: Mixtures

[T77911S]

lifting the sensor plate DOES NOT add air.
that controls fuel ONLY.
air is still limited or controlled by the throttle body.
lifting the pate ADDS fuel. if it runs worse when you lift it then you are too rich.
opposite for pulling down

[SkiVT]

Thanks for the correction (deleted the bad info so nobody gets confused). I should have known I was backwards as the other end of the arm hits the plunger.

[mike sampsel]

Appreciate the information guys.

In the process of troubleshooting I decided to place a piece of cardboard over the mouth of my air intake. I thought well no air the car should die. No it kept on running. When I pulled the accelerator I could feel suction on same cardboard.

Still kept running, expected?

[emac]

This was posted a few years ago- it has helped me

If you move the air plate up slightly with a resulting rough or surge, you are closer to the rich extreme. If you have a 3mm Allen wrench handy, you can turn the mixture screw counter-clockwise to lean it out a little, maybe 1/8 of a turn, then repeat. To get it just right, you’ll have to develop a touch and maybe even a sense of smell. To test for lean, you can pull down on the arm slightly and get the opposite effect of the rich test. That’s it! That’s all there is to it.

[gazzerr]

I don't think you should be able to stall it out covering up the intake. If it kept running smooth with the intake covered then I think that would be a pretty good test for a significant vacuum leak.

This is the best thread I ever saw about using the sensor plate method.

CIS Idle Speed and Mixture Setting Without an Analyzer

[mike sampsel]

Originally Posted by gazzerr

I don't think you should be able to stall it out covering up the intake. If it kept running smooth with the intake covered then I think that would be a pretty good test for a significant vacuum leak.

This is the best thread I ever saw about using the sensor plate method.

CIS Idle Speed and Mixture Setting Without an Analyzer

Thanks for the thread link. I searched for this using rich/lean and struck out.
Knowledge is key

Humm ... and from it I was reminded of a wideband analyzer which I own.
I might ... humm

[mike sampsel]

Originally Posted by gazzerr

I don't think you should be able to stall it out covering up the intake. If it kept running smooth with the intake covered then I think that would be a pretty good test for a significant vacuum leak.

This is the best thread I ever saw about using the sensor plate method.

Yes I think I have a leak somewhere, just can't find it!
Seems some folks (CIS tech troubleshooting guide from Porsche) do not think my leak is significant enough to pursue, because the throttle body idle adjust screw caused the engine to die when I screw it in.

"Don't we wish we could live forever with so much to learn", is a quote I recall from my advanced engineering mathematics professor. This was before my Porsche was a couple of years old . And in a different owners hands.

[mike sampsel]

Originally Posted by SkiVT

This link may also help.

911 CIS Primer - Testing: Mixtures

Good info here, added it to my bookmarks ... thanks
And for my wideband sensor it says 14.7:1. hum
I'll assume my sensor gets installed into the plug off the cat converter ... ?
Probably another thread on this somewhere too ...

[gazzerr]

No worries. Yes agree so much to learn .

The easiest way to find leaks is to smoke test it. You can buy a cheap smoke generator that works with baby oil.

[SkiVT]

This video link is also something I have found useful. There is a specific description of how the plate works with air and fuel.

https://www.youtube.com/watch?v=a4fJAfXYxWk


This pic may also inform your other question on AFR as I think 14.7 is on the lean side of what your year engine might like or at least performance wise, be optimal.