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xflyer
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Joined: June 15, 2006
Posts: 320
Location: SOCAL
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 Posted: Sat Jun 15, 2024 12:31 pm Post subject: Re: AFM signal testing with video |
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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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Mckinleyvillian
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Joined: July 22, 2021
Posts: 596
Location: Bristol County, MA
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| Posted: Mon Jan 30, 2023 7:34 pm Post subject: Re: AFM signal testing with video |
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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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Mckinleyvillian
Samba Member
Joined: July 22, 2021
Posts: 596
Location: Bristol County, MA
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| Posted: Sun Jan 29, 2023 10:59 pm Post subject: Re: AFM signal testing with video |
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| Ahwahnee wrote: |
| Mckinleyvillian wrote: |
| ...What i'm having trouble with is the adjustment. Folks are talking about a "double bend" on the arm... |
I did the double bend and it cured the tracking problem and has worked well for 100,000 miles since. It's the double bend that get the arm back in contact with the track in correct alignment.
Here's the page I followed to do this correctly:
https://www.mye28.com/tech/rods_pages/sitebuildercontent/sitebuilderfiles/afm_by_fr_wilk.pdf
Yeah, for Porsches, but I have no shame.
I did have a spare AFM in hand in case this all went sideways, but I didn't need it. |
Thanks for this.
So, if I’m reading this correctly. I use a 7mm wrench to loosen retainer first, move wiper, then bend?
Can you please explain if by “double bend” I am bending in 2 places on each side of the arm? That’s how I’m interpreting the drawing.
Thank you
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Ahwahnee
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Joined: June 05, 2010
Posts: 10316
Location: Mt Lemmon, AZ
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| Posted: Sun Jan 29, 2023 8:42 pm Post subject: Re: AFM signal testing with video |
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| Mckinleyvillian wrote: |
| ...What i'm having trouble with is the adjustment. Folks are talking about a "double bend" on the arm... |
I did the double bend and it cured the tracking problem and has worked well for 100,000 miles since. It's the double bend that get the arm back in contact with the track in correct alignment.
Here's the page I followed to do this correctly:
https://www.mye28.com/tech/rods_pages/sitebuildercontent/sitebuilderfiles/afm_by_fr_wilk.pdf
Yeah, for Porsches, but I have no shame.
I did have a spare AFM in hand in case this all went sideways, but I didn't need it. |
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Mckinleyvillian
Samba Member
Joined: July 22, 2021
Posts: 596
Location: Bristol County, MA
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| Posted: Sun Jan 29, 2023 5:30 pm Post subject: Re: AFM signal testing with video |
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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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tencentlife
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Joined: May 02, 2006
Posts: 10163
Location: Abiquiu, NM, USA
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| Posted: Tue Oct 15, 2019 4:48 pm Post subject: Re: AFM signal testing with video |
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If it passes the test with no dropouts, the problem is somewhere else.
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mrfusn
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Joined: May 08, 2017
Posts: 76
Location: Portland, Oregon
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| Posted: Mon Oct 14, 2019 11:31 am Post subject: Re: AFM signal testing with video |
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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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tencentlife
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Joined: May 02, 2006
Posts: 10163
Location: Abiquiu, NM, USA
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| Posted: Thu Oct 03, 2019 2:28 pm Post subject: Re: AFM signal testing with video |
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Thanks Kami!!
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kamzcab86
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Joined: July 26, 2008
Posts: 8614
Location: Arizona
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| Posted: Thu Oct 03, 2019 12:11 pm Post subject: Re: AFM signal testing with video |
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| mrfusn wrote: |
| Thanks tencent for the amazing video (I eventually found the YouTube version). |
YouTube version added to the OP, so folks don't have to go on a hunt. 
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tencentlife
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Joined: May 02, 2006
Posts: 10163
Location: Abiquiu, NM, USA
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| Posted: Thu Oct 03, 2019 10:53 am Post subject: Re: AFM signal testing with video |
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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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mrfusn
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Joined: May 08, 2017
Posts: 76
Location: Portland, Oregon
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| Posted: Tue Oct 01, 2019 8:59 am Post subject: Re: AFM signal testing with video |
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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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smd333
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Joined: September 08, 2018
Posts: 57
Location: Maryland
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| Posted: Fri Feb 01, 2019 8:53 am Post subject: Re: AFM signal testing with video |
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tencentlife wow such a helpful video.   ANd thanks to atomatom for putting it on youtube, I couldn't watch it on photobucket at all (that site has fallen into the abyss) |
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tencentlife
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Joined: May 02, 2006
Posts: 10163
Location: Abiquiu, NM, USA
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| Posted: Fri Dec 19, 2014 8:12 am Post subject: |
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| Quote: |
| When you do the test, move the arm very slowly.. there is a time constant affecting the response of the multimeter needle. If you move too quick, the response time of the meter will keep the needle smooth, and you won't notice the wonky signal from the little bit scratched-up wiper track. The ECU will notice.. I don't have measurements, but it definitely samples the AFM faster than my analog multimeter in DC volts |
No, there's no sampling rate with an analog meter like there is with digital, it reads constantly, that's what makes it analog. What you saw was the dropout being too short to overcome the mechanical damping in the meter movement. That actually says it's a pretty well-made movement. In any case, to catch very small dropouts that the ECU will indeed see, the slower the better when you move the AFM vane.
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ohhorob
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Joined: September 26, 2013
Posts: 217
Location: Santa Cruz
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| Posted: Wed Dec 17, 2014 1:53 am Post subject: |
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Here's a quick clip of what a worn-out track on an AFM looks like on a bench-test with an analog multimeter..
Link
I'm using a piece of firm plastic tubing to move the AFM flap (as opposed to moving the wiper directly) I also set my meter to 2.5 volts range, making the needle more sensitive to voltage change (the meters next range up is 10v, and the wonky signal is not as obvious)
I recorded the multimeter and wiper arm together, but edited to zoom and move each to make it easier to see.
When you do the test, move the arm very slowly.. there is a time constant affecting the response of the multimeter needle. If you move too quick, the response time of the meter will keep the needle smooth, and you won't notice the wonky signal from the little bit scratched-up wiper track. The ECU will notice.. I don't have measurements, but it definitely samples the AFM faster than my analog multimeter in DC volts mode!
I ended up spraying with electrical cleaner, and adjusting north just a touch. The signal is a lot cleaner, and a test drive confirms a stable RPM at engine loads that the AFM picks up signal from that area.
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porterbrown
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Joined: February 25, 2005
Posts: 718
Location: Bentonville, AR
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| Posted: Sun Sep 14, 2014 9:22 am Post subject: |
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Thanks!
Tested mine and it passed. Was also a good time to clean-up the filter box inside and out, which was a bit of a mess.
I did notice that the air vane flap and air canal were coated with a very thin coat of grease and dirt. Also noticed that the tube leaving the AFM had a coating of oil and/or gas....either way, it was slightly wet inside. Is this normal?
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heiko910
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Joined: November 15, 2013
Posts: 222
Location: Gardnerville, NV
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| Posted: Tue Sep 09, 2014 5:32 pm Post subject: |
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| denwood wrote: |
| Look up three posts. Same vid, just on youtube |
Thank you, got it. |
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denwood
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Joined: July 29, 2012
Posts: 1047
Location: Thunder Bay, Ontario, Canada
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| Posted: Mon Sep 08, 2014 5:34 pm Post subject: |
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Look up three posts. Same vid, just on youtube
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heiko910
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Joined: November 15, 2013
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Location: Gardnerville, NV
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| Posted: Mon Sep 08, 2014 4:53 pm Post subject: Re: AFM signal testing with video |
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| tencentlife wrote: |
Here's an iddy biddy viddy I took while testing an AFM that was giving some trouble. Symptoms were hesitation off-idle, and intermittent missing while under load in low-mid-range rpms (under 3200rpm).
The Bentley test confirms circuit integrity, but doesn't tell you what you really want to know, which is that the ECU is receiving a variable signal between 0V and 5V that is smooth, uninterrupted, and linear with relation to the air vane position. This test shows the actual signal as the ECU would see it. By the way, this customer had already done the Bentley tests himself with an ohmmeter and found nothing that was outside specs.
You want to use an analog meter; a digital one has a periodic refresh rate so it doesn't do a good job of showing a steadily changing reading, when constancy and steadiness is what you need to confirm. Basically, it's an analog signal, so it is best represented with an analog instrument. You could do the test with a digital meter, but you would want to move the vane very very slowly so you could see the parts where voltage drops out, if it does.
I removed the AFM from the filter box to have access to the inlet so I could deflect the air vane itself. This also obviates the need to remove the cover simply to test the part (although you will need to remove it to repair the meter if it does test as bad). On this particular AFM, moving the wiper hub at top did not show any problems, while moving the air vane did, so even slight pressure on the wiper hub can alter the pressure of the wiper on the track enough to mask a problem.
After unbolting the AFM from the filter box, I plugged it back into the vehicle wiring, and switched on the ignition so the ECU would be feeding it's regulated 5V output into the potentiometer. That voltage is reduced variably by the resistance of the wiper board, and what comes out is the 0-5V signal the ECU needs to calculate air mass. If you have a regulated 5V supply, you could bench test the AFM by inputting the 5V at pin 3.
The voltage signal is on pin 2 (pins are 1-4 left to right when viewed from the rear as installed; they are also numbered on the male connector flange of the AFM), and 4 is grounded inside the ECU, so you want to test V between 2 and 4. Use a low range on the meter; I have this meter on a 2.5V range. Even though the actual reading across the entire scale will be from just above zero to about 4.5V, I'm most interested in seeing the lower half of the range because that's where the wiper spends most of its time, so that's where wear will occur. At idle the signal will normally be around 1V, so at every opening of the throttle it has to sweep thru the area just above one volt. Consequently that is where the most wear will be found, and that is the range that will cause the hesitation on tip-in and load hesitation that this customer complained of.
Clicking on the pic will take you to the Photobucket site. Have the sound up because I'm explaining what I'm doing and what you're seeing.
Here's the URL if clicking on the image doesn't play it for you:
http://s105.photobucket.com/albums/m218/tencentlif...V02923.flv
An AFM that shows dropouts can usually be repaired. First remove the cover, and then I first try spraying the wiper track with electrical contact cleaner while moving the wiper across it a bit to also clean the wiper tips. Then test again.
If cleaning doesn't restore smooth signal, there are two ways to reposition the wiper to run on a different radius of the track. First choice and simplest is to loosen the screws that hold the wiper board down and slide the board toward or away from the wiper hub. In this AFM I couldn't get the screws to break free, so I used the second choice solution. I used a bent scribe and a small screwdriver to make a slight double bend in both sides of the copper wiper arm itself, just enough to move the wiper tips a tiny bit closer to the hub, so it will run on a fresh line on the track. This restored smooth signal output in a subsequent test, and the van now runs smooth and the customer is very happy.
The other test to be done is the Intake Air Temp sensor, which is just an exposed NTC thermistor wired between pins 1 and 4. An ohmmeter and knowing the ambient temperature are all that's needed to check that, according to the temp/resistance table in Bentley. The IAT is very rarely bad, whereas the AFMs physically wear so after 20 years of use it's not at all uncommon to find them in this kind of condition.
The test will be exactly the same with both 2.1 and 1.9 WBX AFM's. It could also be done on earlier L-jet injections, but the pin positions will vary. I think that the signal output on L-jets would be #7, but you would need to verify. |
please help. the video is not available anymore |
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tencentlife
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Joined: May 02, 2006
Posts: 10163
Location: Abiquiu, NM, USA
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| Posted: Mon Jul 21, 2014 6:39 am Post subject: |
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No it's fine there, thanks for keeping it alive, and I see you already fixed it, so that's great.
You might as well make it public too, since it's educational and applies to a slew of other L-jet cars.
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atomatom
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Joined: May 15, 2012
Posts: 1911
Location: in an 84 Westy or Bowen Island, BC
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| Posted: Sun Jul 20, 2014 9:20 pm Post subject: |
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sorry about that - i did think twice about doing it - i erred on cautious by not making it a 'public listed' video (ie, only a direct link can find it).
i will update and give credit to you - unless you want to put it up and i'll just remove my copy. my intent was only to make the video accessible - not seeking fame, fortune or law suits.
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