3.2 air meter - which way will lean / rich

[Porsche_911s]

Apparently I do not know what terms to search for or this is just not done. My 3.2 Euro needs a little fine tuning. The air meter housing was already opened before I bought the system. There were marks on the "spring gear" already from a previous adjustment.

I was wondering if anyone can tell my which way to adjust the gear as in, rich goes counter clockwise or clockwise. I have an LC-1 on a wideband sensor hooked into my laptop. I could make an adjustment then reseal and test. I would much rather make an informed adjustment.

Any thoughts?

My readings as of now are: ~14.6 idle, ~15.5 cruise, ~13.2 WOT.
I'd like to make it slightly richer for cruise & WOT.

Thanks,

[911st]

Someone will get you an answer however, do you have an O2 sensor on your Euro?


I am not an expert but I think the computor will us the O2 loop to modify around your adjustment at idle and cruse.

You may only be able to readjust your WOT results.

Also, the AFM does not have much effect over 5k rpms so you may not have much control over that.

An adjustable fuel pressure reg may give you some control over the top end A/F's.

The best practice might be to get your system as close to stock as possible.

Then get a 911chips custom chip. With this, you could put in his base chip, drive and test it to gather your data. I would put it on a dyno with a good wide band put in the stock O2 location. Test is in 4th and get a print out of the A/F's.

Steve, then will modify your fuel maps and send you a chip that fits your car.

Good luck.

[Porsche_911s]

I have the an SW chip and the Euro does not use the 02 for anything but emissions. Steve could not remember off-hand which way I should adjust the meter to lean or rich the car.

I did not mention the chip because too many debates will start.

Thanks for the response though.

[KTL]

Stephen,

I don't think you're supposed to turn the gear itself by accessing it thru the lid on the airflow meter. You do it thru removal of a plug in the casting. See the picture below from the Porsche factory repair manual. Sorry for the crappy image. It's a scan of a crappy photcopy from the microfiche!

[KTL]

Oops. Forgot the CO level specs






Pelican upload feature automatically resized the last one (idle adjustment) so let me know if you want me to send the full size image of it

[Porsche_911s]

Hey Kevin,

Is that referring to the idle adjustment? The idle CO is adjusted in that manner, or similar manner.

I wonder if there is documentation on what I am tring to do. Now, if there is a tech on the board who "adjusted" the EURO's as they entered the US for emissions reasons, they could say something...

Thanks for the reply, is there another picture of that? Perhaps in the repair book? I may have to adjust the CO at idle after adjustments.

[911st]

I have a "Euro" chip on my usa 85 that takes out the O2 mod.

Ok, playing with the AFM will probably not effect the idle map. That is done with the air bypass I belive.

Again, above 5k you still have the same problem with loss of fidelity from the AFM.

Thus, you will gain a bit of tunability in the mid range on the WOT map and the cruse map. It may be that you get what you want on one, but not the other.

That is, if you move your relitive position of the AFM to get you goal at WOT, it will effect the cruse map to.

Why not have Steve burn you a chip that achives your goals? I think it is only $150 if you did not elect the custom chip option in the begining.

If no one can tell you, you might put a volt meter on it, move the flapper and see.

[Steve W]

Stephen, I have an open AFM in front of me right now. Tightening the spring tension by turning the wheel clockwise will lean the air/fuel ratios, and vice versa. Judging by your posted AFRs, you are close to spot on. Best fuel efficiency at cruise is at an AFR of 15.2:1, best power at full throttle for most 911 motors are between 12.9 to 13.1:1 Best compromise for low emissions is at 14.7:1. As 911st noted, on the average 3.2, the AFM flap bottoms out by ~5000 rpm, so adjustments to the spring have little to no effect after this.

[KTL]

The first image is for adjusting the mixture/CO %. Look at the bottom left of the picture and it tells you clockwise is to go richer and counterclockwise is to go leaner. The middle image tells you the acceptable CO level % for a Euro car. It's 1.0-1.5

The last image is the idle setting which I understand is completely illegible since it was resized by the board image posting function. Sorry about that.

All of the above images are microfiche prints of the factory repair manual (NOT the Bentley manual) so if you know of someone who has the paper hard copy of the manuals, the images I posted are in there.

[Porsche_911s]

I should have taken a baseline before making any changes. However, I did not have the O2 bungs in my exchaust and I made some changes before getting the LC-1 up and running. DOH!!

[ianc]

Hi 911s,

Moving the toothed wheel in the AFM should only be done as a last resort if you can't get adjusted within spec using the 3 mm allen head.

The direction to turn the spring is simple if you think about it. Look at the way the spring is wound. Tightening it will mean more spring tension, less air flapper deflection and hence a leaner mixture. Loosening it will do the opposite. HTH,

ianc

[Porsche_911s]

Thanks Steve for the response! The cruise was the only reading I was concerned about. I think it should be a little richer. Not because the LC-1 says so, but because I still get some slight bucking just below 3k (off and on). It seems it is a little too lean at the lower RPM.

And Steve has been really helpful making the 3.2 a pleasure to drive. It had another aftermarket chip when I bought the engine and the car was difficult to drive. With his chip and his help, my wife had this simple statement, "Wow, it drives like a normal car!"

Thanks,

[Porsche_911s]

Hi Ianc,

I thougth about the idle adjustment as well. But since the idle is already going towards the rich side, making it richer to help with the cruise did not seem like a good choice.

[911st]

Could something else be a problem?

One of the biggest cause of drivablility and rarely checked, is a dirty fuel filter.
Maybe check the spark plugs & gaps...
Fuel pump could be lazy.

I have been wanting to replace the WOT switch with a normally open vac switch set to close or trigger any time acceleration is called for with application of throttle. Currently we have to floor it all the way to triger this.

However, SW eluded to there being some type of programing in the chip that with a movement in the AFM door triggers an enrichment cycle for accel, if I understood correctly.

Is your flaper door moving freely?

[Porsche_911s]

I'll update the thread once I get the time to make the suggested changes. We'll all know then. Until then, its just speculation. With the LC-1, it makes it easier to see the changes.

[2.7RACER]

Stephen,
You mentioned some slight "bucking" just below 3000 rpm.
A common failure of the AFM is wear at the trace, particularly at the most common rpms.
A volt meter at the AFM input to the DME control unit will reveal if the voltage is jumping around, indicating a worn trace.
You can sometimes move the arm in or out so it works on an unworn part of the trace, if at hasn't already been done.
This has been covered ad nauseum on this board. Search AFM.

[Porsche_911s]

Hey Doug,

That was one of the items Steve had me do when I first had the cover off the AFM. Good point, mine was not worn that bad but I am sure it helped.

The slight buck to me seems like a lean issue. After tuning carbs on my 2.7 and then tuning the Megasquirt system, I get the same feeling as I did when I had those running a little lean. I keep a log from the LC-1 so I know the car is running leaner than 14.6 at the point of a buck. It normally is in the upper 15 range.

The buck could be a whole list of things. I just want to get the idle, cruise, and WOT set as close to recommend settings as possible. I figured I'd start with a solid baseline before moving forward. The car really does run well. I am just obsessive…

[2.7RACER]

Stephen,
Since you are confident the trace is ok, turn the wiper arm slightly counter clockwise.
Like maybe 1/8 inch on the trace.
This will slightly richen the mixture. It will either help or move the bucking to a lower rpm.
If the bucking moves to a lower rpm, time to get a new or rebuilt AFM.
I run my '85 this way with the O2 sensor disconnected, because it is trying to lean things out.
You may need to adjust back and forth just to see what works best.
Since you have a euro 3.2 probably no catalytic converter.
Rich uncontrolled adjustments can ruin a cat in short order.
My '85 runs fine, no smog checks where I live.
It would not run smooth when cold, before I changed the AFM setting.

[ischmitz]

Steven,

Why wouldn't you start with adjusting the 8-position fuel quality switch on the Motronic before tinkering with the air flow meter? This switch allows you to richen up the mixture. Read here for a lot of good information: http://www.frwilk.com/944dme/ It also talks about the AFM and how to refurbish a worn AFM. At the very bottom of the AFM page is the stern warning:

"Dont do it! Never change the tension of the spring on your AFM. You will destroy the calibration of your AFM. The AFM is laser trimmed to a fine tolerance by BOSCH."

[Porsche_911s]

The fuel quality switch was another item Steve had me change right away. Warning or not, the PO had messed with the AFM & an aftermarket chip. Change was already made.