AFM signal testing with video

[mrfusn]

Thanks tencent for the amazing video (I eventually found the YouTube version). These were my exact symptoms (see here)—hesitation off idle and occasional stutter under load under 3200rpm. I too could not get the plate off, but bent my sweeper and confirmed a solid, smooth transition between 0v and 4.5v. I had a drop to ground right above 1v as mentioned, and if you look veeeeerrrrrry closely, you can see the issue.

Thanks again!

If you look very closely at the region just above the middle of the word, you can see the track wear.
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‘86 GL 2-knob Syncro Weekender w/ Subaru EJ25
'85 GL sunroof turned pop top w/ WB 2.1

[tencentlife]

Glad it helped. Wear in the sweep just above idle is by far the most common problem with aged AFM's, apart from that they are exceedingly robust with very little else that ever goes wrong. That common wear is simple to test for, as you found, just as easy to repair on your own. Given that the so-called rebuilt ones are often no better than the one you sent in, and the worst you can do by repositioning the wiper is to cause a new wear track to form such that the additional life of the thing you gain is only 100k miles in addition to the 200k+ miles it took to wear the first time, it's really a no-brainer to just fix and retest the one in your hand and save the 2 or 3 hundred bucks.
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[kamzcab86]

[tencentlife]

Thanks Kami!!
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[mrfusn]

Can Chris or someone else speak to why this would also affect load around 3k RPMS as well? Sometimes I’m still seeing that, despite 100% of the time fixing the low RPM off idle issue (hundreds of miles driven now to confirm).

I didn’t see any other worn spots, and the voltage increase was smooth, so I’m trying to puzzle out why in the original post this would be an affected area also, and what I might be able to further diagnose.
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‘86 GL 2-knob Syncro Weekender w/ Subaru EJ25
'85 GL sunroof turned pop top w/ WB 2.1

[tencentlife]

If it passes the test with no dropouts, the problem is somewhere else.
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Please don't PM here, I will not reply.

At birth you only know how to suck. Spend the rest your life learning how not to.

[Mckinleyvillian]

hey tencent, this is a great tutorial. pretty sure it's helped me track down my idle issues. the tracks inside the AFM are very, very worn and V drops right where expected when tested.

What i'm having trouble with is the adjustment. Folks are talking about a "double bend" on the arm- which is what i've got to do since my screws aren't getting loose

not really sure what i'm doing with something so delicate. tried bending it a little but now it's lifted up and i've got 0 v.

any advice on how to do this without further damaging the equipment is much appreciated. thank you
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so many roads i know
all i want is one to take me home

85 Vanagon GL 1.9 stick

[Ahwahnee]

[Mckinleyvillian]

[Mckinleyvillian]

well, haven't gotten the AFM back in the van yet but while testing, voltage drops have ceased and there's a steady, within spec increase all the way across the track.



this video was very, very helpful.


Link


ended up removing the arm via 7mm bolt as shown in the video. made the whole shebang much easier.

gonna let it sit with RTV on the cover overnight and see what happens after work tomorrow
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so many roads i know
all i want is one to take me home

85 Vanagon GL 1.9 stick

[xflyer]

Mckinleyvillan, That video can get some people into trouble. First is the description of the "idle screw" which actually regulates a bypass port around the spring loaded flap. Turning is clockwise RICHENS the mixture and counterclockwise LEANS it. And its not an "idle" adjustment, but will effect any engine speed with low air flow. Unless someone is knowledgeable and experienced, preferably with access to an exhaust analyzer, that screw is best left alone. Certainly on vehicles with an O2 sensor, which most Vanagons have.
Same with the clock-spring that returns the air flap. I've had to fix many of those that were changed by others in attempts to fix running problems. This happened on VWs, BMWs, Porsche, and Nissan. In some cases a new AFM was required. Will never know if the AFM needed replacement before the insides were disturbed.
Also if someone wants to add the wire to the flap arm, they should use #22 or 24 teflon insulated wire which is very flexible and is less likely to cause problems.
As always, DO THINGS YOUR WAY.
YMMV
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1989 Campmobile, 1984 7 passenger beater Vanagon
Both with cool A/C