[3.2 Motronic] Air Flow Meter wiper arm re-tracked - WOW!

[Pstallo]

Where in the engine compartment is the AFM? Is it difficult to remove/get to?

[dentist90]

Same here Arne! My car was ok at idle, but as soon as I touched the throttle and the idle contact switch opened the car would buck and surge if I tried to drive slowly, say down the driveway. When the idle switch opens the DME looks for a signal from the air meter. As you can see from my photo the tracks have worn through near the idle flow position. Repositioning the wiper arm totally fixed the problem. I can creep along just of idle all I want now without the bucking/surging!
I was very conscious of the pressure the arm places on the contact strip: hopefully it does not wear thru prematurely.

[dentist90]

Originally Posted by Pstallo

Where in the engine compartment is the AFM? Is it difficult to remove/get to?

Not hard to get at or out, but a little tricky to get open. The lid is sealed on with some type of glue/weather sealant and you have to carefully cut and pry it open. And of course, seal it shut afterward!

[NY65912]

A question that I have been pondering.......what can be done to "re-coat" the wiper area to get rid of the tracks and have a "new" consistent wiper area???

I am not a materials expert nor really know anything about AFM's so I shall differ to those smartrer than I. I just feel that there must be a way to truly rebuild that area.

Cheers

[Rleog]

Thanks to Arne2, Steve Wong, and all who have taken the time to post on this topic. I'm now armed with some information on the AFM function, a topic I little understood.

[Elombard]

Originally Posted by NY65912

A question that I have been pondering.......what can be done to "re-coat" the wiper area to get rid of the tracks and have a "new" consistent wiper area???

I am not a materials expert nor really know anything about AFM's so I shall differ to those smartrer than I. I just feel that there must be a way to truly rebuild that area.

Cheers

Yes - exactly, I am suprised this is not possible and at a reasonnable price.

[kidrock]

Originally Posted by NY65912

A question that I have been pondering.......what can be done to "re-coat" the wiper area to get rid of the tracks and have a "new" consistent wiper area???

I am not a materials expert nor really know anything about AFM's so I shall differ to those smartrer than I. I just feel that there must be a way to truly rebuild that area.

Cheers

Probably composed of "Unobtainium Substrate".

[Arne2]

Obviously, restoring the worn tracks would be the preferred method. But it would be critical that the material used to re-coat the worn tracks have EXACTLY the same resistance as the original. Otherwise the metering would be off.

It would seem that re-coating would be what has been done to "re-built" unit. Judging from Steve's comments about over-rich mixtures with rebuilt units, it would seem likely that the rebuilders have not found the correct coating to duplicate the factory resistance.

[dshepp806]

My first pass on this wiper assembly (a long time ago,..with no running problems at the time), was completely "preventative". Being an engineer, naturally I brought out the instrumentation to measure it's functionality. I used all manners of assessment to include the old fashioned analog tube meter for resistive sweep measurements,...a very clean DC power supply for voltage sweep measurements,...and (ultimately) my o-scope to look for the "faintest" of anomalies. Amazingly, all looked good for an original 1989 AFM that's seen about 133Kmiles. Even seeing wear tracks, I detected no difference in resistive sweeps. SO, opted for a cleaning on this round.

Nonetheless:::::

I gave her a good treatment of 2-3 different Caig products (being an audiophile, my lest step was to coat all copper with pro gold) while using a very thin burnishing piece to clean the arm contact point. Everything was nice and shiny when done. I was lucky in that my wear didn't result in various compromises of the copper trace. So,..no toucha' of any screws in this module. YMMV.

Post work test results were the same, but I felt better knowing that all copper was deoxed, burnished, cleaned and treated. That was about 5 years ago,...... Being a closed unit, one doesn't see much dirt and such inside of it. Moisture is well controlled but could be a contributor to unnecessary resistance.

I do understand the posts relating to wear manifesting in compromising the copper arc. Open or incorrect resistance will wreak havoc, for sure.

Just a short (old) story: I think I went INTO my AFM later into my first year of ownership. I shared this story with a Porsche friend. Many months later, he decides he will dive in to his 87 AFM and check/do the same. I get a Saturday call from him , stating he was having problems. Long story short, he was using an auto-ranging DVM and was erroneously reading the meter's scale change as being a problem with connectivity during his sweep. He says "geeze, it's happening at the same spot every single time". (no sheeit...)

Of course the call to me didn't happen AT THAT POINT, so he decides to make a positional adjustment himself. Unfortunately, bozo decides to turn the damned hex head and reclocks his AFM (wrong screw). Why? I don't know. He had problems until this was resolved.

Nonetheless: nothing like fresh NEW shiny copper in ALL manners!!!!

BEST!

Doyle

[Hnichols]

A basic question: if you experience surging and bucking and low rpm but only when the motor is cold (and even then only now and then), would hat eliminate AFM wear as a cause? I would think that if the tracks were worn, it would happen all the time, hot or cold (??)

[Tippy]

I've pondered putting through hole resistors where the embedded resistors are at where I smoked the AFM doing this test.

Redoing the track is pretty much impossible AFAIK.