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ianc's Avatar
 
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FR Wilke's AFM mod a success (and easy)

Hi folks,

I had some dissatisfaction with the initial tip-in response of my car. The off idle response was not what it should have been in terms of getting an immediate response when first pressing the accelerator. I was also experiencing a severe transition between idle and off-idle when decelerating. For example, when moving along in traffice at very low speed, transitioning between a very slight throttle input and none at all would create a jerk in the car's motion.

Having read a bit, I decided to try FR Wilke's modification to the AFM, which is detailed here under the 'Refurbishing your AFM' section:

http://frwilk.com/944dme/afm.htm

It's a very easy procedure to do. Just remove the AFM, carefully cut away the factory glue\sealant around the black plastic cover on top of the AFM potentiometer, then use a 7 mm. wrench to loosen the clamping bolt. After loosening, you can slide the wiper assembly up or down on the shaft to allow the wiper to contact a different (new) area of the ceramic substrate resistor. I moved mine down. This is easier, since moving it up would require bending the wiper itself. After retightening the 7 mm., I applied a thin bead of sealant around the groove in the plastic cover, refitted it to the AFM and allowed it to dry, then reinstalled the AFM in the car.

I'm happy to report that after doing this, the throttle response is more immediate, making it easier to move off at a light or stop sign, or to match revs when downshifting, and the idle\off-idle transition issue is significantly reduced.

Very easy to do and well worthwhile if you're having these types of problems. Good luck,

ianc
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Last edited by ianc; 06-15-2006 at 01:33 PM..
Old 06-15-2006, 01:00 PM
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I've been thinking of doing it too: Your link is broken I think, try this one:

http://frwilk.com/944dme/afm.htm

Did you do the "hotwire wiper" jumpers too? How scored was the substrate on your car, and how many miles?
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Old 06-15-2006, 01:30 PM
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Thanks David, I fixed the link.

I did not do the hotwire jumpers, no. The substrate did not appear very bad actually. There was a pair of thin black lines scribed in it which were worse down near the idle position, fading off to next to nothing near WOT. It looked very similar to those pictured on Wilke's page actually. Car has about 135K on it. Give it shot, it takes about 15 min.

ianc
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BMW 135i. Nice. Fast. But no 911...

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Old 06-15-2006, 01:36 PM
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Thanks My car has 109K, and I'll bet 90% of it's life has been spent with the wiper in the first 15 degrees of the arc of the substrate. My car is great from 3500K up (esp. with the turbo) but it feels like there's a lack of response in the lower revs.

I'll post back too once I've got 'er done. I like that there is nothing to buy for this one, unless you break something
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Old 06-15-2006, 01:40 PM
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I chased a hesitation/surging problem for over a year before have the nerve to try this. It was the fix for me.
Great throttle response ever since.

I have considered that there should be a place to have the afm completely rebuilt. Anyone have a line on that?
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Old 06-15-2006, 04:29 PM
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I just happen to have a spare AFM in my crawl space that I got when I bought a spare airbox to cut up. Thanks, I'll try that . . .

Another Ian
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Old 06-15-2006, 04:53 PM
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Yes, do. After three days, the only negative effect I can report is that I have to relearn how to squeeze the throttle when moving off. I'm giving it way too much gas now!

ianc
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Old 06-16-2006, 09:31 AM
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Is this a mod or are you making it work like new?
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Old 06-16-2006, 10:18 AM
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Quote:
Is this a mod or are you making it work like new?
Both, in a way. Take a look at the link. You are essentially just moving the wiper assembly up or down on the shaft to allow the AFM wiper to contact a virgin strip of resistive material on the substrate. Think of it as an 'adjustment'. No new parts are added,

ianc
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Old 06-16-2006, 10:25 AM
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Instructions are for a 944. Do we use the same AFM?

Quote:
Originally posted by ianc
Both, in a way. Take a look at the link. You are essentially just moving the wiper assembly up or down on the shaft to allow the AFM wiper to contact a virgin strip of resistive material on the substrate. Think of it as an 'adjustment'. No new parts are added,

ianc
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Old 06-16-2006, 10:33 AM
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Quote:
Instructions are for a 944. Do we use the same AFM
Part #'s are different, but the principle of operation is the same, and doing this will be equally beneficial for a 911 with the DME.

ianc
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Old 06-16-2006, 11:04 AM
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ianc, this is a thing that is happening to me almost anytime I'm in stop and (slow) go traffic. The car would jerk to the point of making me pull over and wiat for traffic to clear, I couldn't stand it.

I've never noticed it before with my old Autothority chip. I bought a SW chip and I noticed it to be really bad. I emailed Steve and he thinks it's not because of the chip. This was about a year ago and I've left it alone just trying not to take my car out in rush hour traffic. But now I'll have to try this, what seems to very simple task!

Gosh what's other neet things will I read on this great forum. How to instal a paper clip in the thing-a-ma-jig and get 50 more hp? i wish.



se
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Old 06-18-2006, 06:20 AM
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Ianc,
Excellent post! Thanks.
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Old 06-18-2006, 06:36 AM
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What year 911's is this mod applicable to? Only Carrera's (84) and newer?
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Old 06-18-2006, 07:03 AM
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This is for motronic afm which I belive is only 84 thru 89 carrera.
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Old 06-18-2006, 09:05 AM
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It's a good procedure and I highly recommend it. High track resistance from wear, and spots where the resistive film is completely gone will cause all kinds of havoc with part throttle driveability with signal dropouts and lean mixtures. The 964s use the same AFM, and wear on their substrates is just as bad if not worse. The AFM is mounted upside down on the 964, and sometimes you'll find lots of motor oil inside there too.
Old 06-18-2006, 10:51 AM
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Steve, do you know of anyone that restores/rebuilds them?
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Unlike women, a race car is an inanimate object. Therefore it must, eventually, respond to reason.
Old 06-18-2006, 10:57 AM
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I have just performed the same repair/wipe path redirecting and noticed a dramatic improvement in part throttle smoothness and idle. Initially I did not mess with the mixture adjustment allen screw. I have never touched this adjustment and it had not been adjusted since 2004. Moving the PCB around may have altered something. Anyway, I have just returned from adjusting my CO mixture screw. There was still some hesitation and sluggishness so I figured I would go leaner (unscrew the allen screw, allowing more air to bypass the flapper). I started with 1-1/2 turns with some success. I then went to 5 turns with a dramatic improvement. I played around and in the end I settled for 3-1/2 turnes more open (leaner) than my original setting. The car was fully warmed up, has no vacuum or air leaks, fresh plugs, wires, cap, O2 sensor, cat converter. The car runs much better at part throttle now. Smoother with a little more agressive tip-in. The idle is more stable now as well. I do not have an CO meter.

The substrate was worn completely through on the first 1/4-1/3 of the arc (idle and part throttle). The car has 220k and it the AFM looked as if it had never been opened. One other curious thing was that the casting date of the AFM body was 1982 and my car is a 1984 model.

A big thank you to Joe Garcia who provided the catalyst to get me reading the various threads on the subject.
Old 06-18-2006, 11:56 AM
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Jerry, not that I am aware of. The above is more of a procedure to correct for a wear problem. There isn't much of anything else that can go wrong with them, but if it is that physically damaged that the above doesn't work, purchasing a new meter or a good used one would be a better bet.
Old 06-18-2006, 12:21 PM
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I did the correction on mine already and it worked. I just figured it was a somewhat temporary fix though.
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Old 06-18-2006, 12:29 PM
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