Afm Sorted....but For How Long?

[lagonda 42]

Having put up with the cutting out (well, reverting to idle) and jerky-jerky for far too long, I at last found time to get the AFM off and have a look at it.

 

Probably around 10 years ago, I'd done the trick of repositioning the carbon track pick-up arms so that a fresh area was swept. Looking at it this time, there's no evidence that the resistance surface has worn through.

 

With a multimeter, I found the resistance track was reading well over 1k ohms for the higher readings. Hmmmm. I've previously done the trick of repositioning the copper contact arms, so this time, I soaked a cottonwool bud in nail varnish remover, and scrubbed the resistance track vigorously with that. Quite a lot of dirt came off; result, maximum readings now around 800 ohms.

 

No jerky jerky....why did I put up with it for so long?!

 

But....question....will this prove to be a reasonably long term fix, or should I be looking at getting the afm reconditioned/a new one? Have had the car since 2003 so I don't mind spending out if it's a worthwhile and long term improvement. As far as I know, it's the original afm, supported by the date code, so it will have "done" around 211,000 miles.

[estland 3]

I don't see a reason if the track isn't worn

[lagonda 42]

There doesn't seem to be any undue free play in the flap bearings, which would seem to be the only other wearing item.

[GLPoomobile 958]

You mentioned flap bearings, but the other thing that can go is the spring tension on the flap.

[lagonda 42]

Hi,

 

Spring return seems pretty positive...wonder if there's a tension test, perhaps with a spring balance?!

[GLPoomobile 958]

Not sure how to test them, but spring tension certainly is important and needs to be set correctly. For a given flow of air through the AFM, the flap could move more, or less, depending on the spring tension, and so the arm will move more, or less, across the carbon track, thus altering the fuelling.

[lagonda 42]

Hmmm. Perhaps it's something that could only be resolved on a rolling road. It starts and idles well, plus fuel consumption is certainly OK, but performance has always been less than I perhaps unrealistically expect...I know Gtis are lighter, but certainly the only GTi I've driven was zippier.

[GLPoomobile 958]

Actually, I remember now that there is a way to test it. It involves connecting a battery to certain terminals whilst measuring "stuff" at other terminals and comparing to data. Vague I know but it's all I can remember. For some reason I've got it in my head that it may have been Steve@Cornwall on here that detailed the process.

[johnhenry 20]

i suffered the 'how long will this not break for' with my AFM.

 

I ended up going to ATP electronics, sending it away and getting it rebuilt, i think this is just retracking as you've done. But its come back with a warranty and It feels amazing, no jerkiness, and has got rid of a lot of other niggles in the system!

 

It costs abit, but for peace of mind, it was my only option really. Very pleased with it.

[lagonda 42]

Yes, I've done all those tests .... actually detailed in the Haynes manual...and all the readings do now correspond....they certainly didn't before!

 

I'm happy enough to pay for reconditioning.....but I suspect it would be a lot of money for no improvement over what I've done....the car is certainly running beautifully now, a huge transformation. Incidentally, I would expect reconditioning to at least involve replacing the resistance track board with a new one...if all they do is retrack the existing, they're doing no more than I've done.

[johnhenry 20]

Yes, I've done all those tests .... actually detailed in the Haynes manual...and all the readings do now correspond....they certainly didn't before!

 

I'm happy enough to pay for reconditioning.....but I suspect it would be a lot of money for no improvement over what I've done....the car is certainly running beautifully now, a huge transformation. Incidentally, I would expect reconditioning to at least involve replacing the resistance track board with a new one...if all they do is retrack the existing, they're doing no more than I've done.

 

You would have thought so wouldn't you! It doesn't though :/ I asked them specifically if it did - they said no :/

 

all i know is they have been through it and its never felt this good, the idle is rock solid - no hunting, pulls great through the range. and also comes with the warranty.

[lagonda 42]

Hmmm, can't see there's much else to "recondition" other than, as GLPooo...says, the return spring tension. To be fair, if replacement resistance tracks aren't available you couldn't expect replacement, but it's a Bosch AFM and I would have thought Bosch would still be supplying spares such as that.

[DamirGTI 342]

There was an firm near by my local which was mainly specialized in selling Bosch line automotive stuff , and apart from that they where also main depot for various engine management sensor diesel fuel pumps units etc. collected from the entire country (from various car/hgv services/shops shipyards industry machinery etc.) to be sent to Germany for rebuilding/repair/overhaul by Bosch .. i wanted to send my AFM too to be rebuilt but the price was a bit too much for me that time , mainly because there was still lot of spares to be found at the scrapyard cheaply ... anyway i asked a guy who used to work there what they do to these vane AFM's while rebuilding them , said that they do not replace entire potentiometer unless it's damaged (broken , cracked etc.) they clean up the entire carbon track and apply new one , replace the wiper arm and laser adjust/trim them to the specs.

 

D

[lagonda 42]

Well, cleaning up the carbon track proved a fairly temporary fix. Re-cleaning hasn't sorted it...the track has no obvious worn patches so I've been looking for problems elsewhere.

 

But fitting another AFM has fixed it! I'd happily pay for a fully reconditioned one, but not if that doesn't involve a new carbon track.

[farmer 328 1 Cars]

Some new AFM on eBay for about 200 Euros plus carriage.

 

The XU9JA one's

[ALEX 98 1 Cars]

After cleaning the tracks make sure the cover is sealed to stop them corroding.

[stumpyjag 6]

Not sure if this helps but I have used this guide I found on here a long time ago. It's for a Porsche 944 but the same afm and is very detailed.

 

http://www.the944.com/afm.htm

[idoari 10]

WOW. i just wanted to open a topic about the same thing. i have the same problem with my AFM.

 

NEVER touch the spring tension IMO! it set in the factory by bosch and getting it right after you loosing it it's very hard!

 

even if i get a Brand new AFM the problem is still going to come back some day because of the Inherent design of the vane type AFM.

 

since i'm electronic engineer i thought to try to retrofit "hot wire AFM" to replace the vane AFM (and if necessary design a circuit to make the signals the same) . the problem is that i need to characterize the old type and the new in order to know what output voltage getting out in a giving RPM - and i need a new one to do it and a load of equipement.

 

i also know that the output signals of the two types are differnet as you can see here:

http://www.tiepie-automotive.com/en/Measurement_examples/Sensors/MAF_Airvane

http://www.tiepie-automotive.com/en/Measurement_examples/Sensors/MAF_HotWire

 

- it won't be easy but i think in the long run it will be worth it since hot wire AFM are FAR more reliable.

[steve@cornwall 100]

For some reason I've got it in my head that it may have been Steve@Cornwall on here that detailed the process.

Far too technical for my style I'm afraid

[scbond 15 1 Cars]

Actually, I remember now that there is a way to test it. It involves connecting a battery to certain terminals whilst measuring "stuff" at other terminals and comparing to data. Vague I know but it's all I can remember. For some reason I've got it in my head that it may have been Steve@Cornwall on here that detailed the process.

Easier to leave the cap off, fit it to the car, plug it in and switch ignition on. Then use a multimeter to test the pins on the back where they meet the board.

[Mikey S 29 1 Cars]

Hmmm. Perhaps it's something that could only be resolved on a rolling road. It starts and idles well, plus fuel consumption is certainly OK, but performance has always been less than I perhaps unrealistically expect...I know Gtis are lighter, but certainly the only GTi I've driven was zippier.

If its feeling a little gutless, check the distributor advance weights havnt seized. In my 1.6 they were seized and freeing them up made a world of difference to it.

Edited May 31, 2015 by Mikey S