Afm Identification And Testing

[scbond 15 1 Cars]

Ok, I know how to test the AFM but I have a bit of an issue with doing so. I follow the guide for testing assuming the AFM is for a Jetronic (which it should be) but when testing pins 7 (flap signal) and 5 (earth) I get 224 Ohms at all times (all through the wiper track). I then tried assuming it as Motronic and when I test pins 2 (flap signal) and 4 (earth) it starts at ~560 Ohms closed and then goes up to ~1600 Ohms and then back down to ~600 Ohms.

 

Obviously doesn't seem right at all. The cap is the right part number (0 280 202 109) but the only testing that works seems to suggest it's a Motronic unit. Assuming that the internals are slightly different between the two I took pictures to see if anyone can confirm which the AFM actually is.

 

 

 

 

While it was open I did notice that the wiper ran off the track when the flap was closed, which may explain the poor starting and occasional rough idle etc.? I adjusted that and put the wiper on a new track as best as I could.

[welshpug 1,620]

if it has a bypass screw then its Jetronic, which ties in with the part number, if it has a Potentiometer its Motronic.

[scbond 15 1 Cars]

Is that the 5 mm hex mixture screw? If so, it has that. I'm guessing the only way test test it properly is to hook a battery up?

 

This raises another point actually...is the mixture screw supposed to come out when fully undone? Mine won't.

[DamirGTI 323]

Apart from the mixture screws , the actual outside body shape of the two AFM's is also just a little bit different .. but the most obvious difference is this plastic surrounding which covers pretty much entire potentiometer plate area on the Motronic AFM's (neither one of the Jetronic AFM's doesn't have this) :

 

 

 

... 8v Motronic 1.3 AFM is actually identical to the ones on the Mi16 engines , they're same units .

 

Don't bother with resistance readings , for potentiometer track check do voltage testing you need to force the voltage into it first , plug it back on the car and back probe the connector with ignition ON or buy an 9V battery and connect it on the AFM as described in this article (read down below) :

 

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

 

... also , using analogue multimeter would be best if you have one .. digital multimeter reads too fast so it's much harder to pinpoint "flat spot" on the potentiometer track as the voltage wave increases/decreases while moving the wiper arm , analogue multimeter is much better for this .

 

There's nothing wrong with the wiper arm pointing down the track like so with the engine OFF , as soon as you start cranking the engine it'll bounce/move up it and whilst running/idling it'll climb up from this the rest spot .

 

The mixture screw has an O-ring underneath the threads on the end of it , which kinda makes it stay inside when you unwind the screw up to the top , so when you undo it completely us an screwdriver/pliers to fish it out or simply while undoing and once the bolt is off the threads jam the allen wrench a little bit on the side and pull up and the screw should pop out .

 

D

Edited May 1, 2014 by DamirGTI

[scbond 15 1 Cars]

Cheers buddy. Have seen that website article thanks to you and have been following it as much as possible.

 

As for the wiper arm being off the track...with the flap closed it wasn't just slightly off the end of the track or anything, it went beyond the circuit board fully. I'm assuming that may cause issues? If not then I'm stumped all over again

[Bobbafett 49 2 Cars]

DamirGTI do you have a link or the method for testing the motronic AFM? I bought a brand new one a couple months back (aftermarket) and I think it's possibly playing up already.

[DamirGTI 323]

it went beyond the circuit board fully. I'm assuming that may cause issues? If not then I'm stumped all over again

 

 

If it went off the track/potentiometer completely then somebody must've been tampering with the spring tension or wiper arm position on the shaft , or it could be missing flap stop , this piece on the inlet side of the AFM held by two screws :

 

 

 

 

... if the flap stop is there as it should , the try to tense the flap spring - mark initial position , unhook the clip and start by adding 1 tooth more on the clockwise side (rich) .. and see what happens ... can add more but i'd not recommend more than 4 tooth's , at least not without checking the mixture while doing so . Check the phillips screw on top of the wiper arm also , it should have an blob of clear sealant over the screw as all of them have it from the factory , that should indicate that the wiper arm position on the shaft is intact thus no correction/adjustment hasn't been made cos you need to break the sealant in order to do so .

 

Also , noticed on you're second pic. that theres some white areas on the carbon track (this'll make problems for sure) , also the track looks a bit grooved so either reposition the wiper or the potentiometer plate so that the wiper slides across fresh carbon track surface .

 

D

Edited May 2, 2014 by DamirGTI

[DamirGTI 323]

DamirGTI do you have a link or the method for testing the motronic AFM? I bought a brand new one a couple months back (aftermarket) and I think it's possibly playing up already.

 

 

You can use the article on the link above for testing the Motronic AFM as well .. procedure is same for both .

 

D

[scbond 15 1 Cars]

 

 

 

If it went off the track/potentiometer completely then somebody must've been tampering with the spring tension or wiper arm position on the shaft , or it could be missing flap stop , this piece on the inlet side of the AFM held by two screws :

 

 

 

 

... if the flap stop is there as it should , the try to tense the flap spring - mark initial position , unhook the clip and start by adding 1 tooth more on the clockwise side (rich) .. and see what happens ... can add more but i'd not recommend more than 4 tooth's , at least not without checking the mixture while doing so . Check the phillips screw on top of the wiper arm also , it should have an blob of clear sealant over the screw as all of them have it from the factory , that should indicate that the wiper arm position on the shaft is intact thus no correction/adjustment hasn't been made cos you need to break the sealant in order to do so .

 

Also , noticed on you're second pic. that theres some white areas on the carbon track (this'll make problems for sure) , also the track looks a bit grooved so either reposition the wiper or the potentiometer plate so that the wiper slides across fresh carbon track surface .

 

D

 

 

 

Already did the wiper arm. It did have the glue in it so not sure if that's been tampered with. The flap stop is there too so possibly the spring tension has been tampered with in the past? To be honest, I wanted to avoid touching the spring tension at all costs but might be all that's left. Retracked and fixed the arm and did a setup on the throttle and idle air bypass screws (along with the sensor) and the car still struggles on cold start and hunts a little on idle. Had to adjust the screws in a slight different way to the Haynes manual. Basically I set it to initial position and started the already warm engine and it will just stall. The issue is that it'll already be around 650 to 800 RPM and will fluctuate between the two until I bring the air screw up beyond 1,000 and then turn the throttle back in to lower it to 1,000.

 

The CO idle mixture screw is at ~8.5 turns out and I still get a very slight smell of petrol at idle (sometimes). Any further out and I'll get smoke out of the exhaust when I touch the throttle.

 

What sort of tension should the spring be on? All the markings on the gear are the same. And to be honest, the tension feels fine to me...but obviously I don't have experience of a stock one.

 

Fairly certain the issue is the AFM now as the hoses are clear, the SAD works and I've set it up as best as possible according to the Haynes.

[DamirGTI 323]

If it smells on petrol , smokes (what kind of a smoke ? is ti black ? also the plugs are they black covered with sooty deposits ?) hunts and rmp varies then it's likely the rich mixture which is the cause ..

 

Aside from the AFM , have you tried replacing the ECU temp. sensor ?

 

AFM spring tension/cog wheel is laser trimmed from the factory - theres no markings what so ever .. it's really hard , or could say impossible , to tell by feel up to what extent the spring tension should be preset on a tense/loose side for proper function of the unit based on the engine requirements . Precise adjustments can be done only with an aid of either a wideband lambda sensor along with the gauge or the exhaust gas analyzer .

 

If the ECU temp. sensor and it's connector/wiring are sound , try playing a little bit with the AFM by connecting the multimeter on the output terminals measuring voltage while working and manually opening/closing the flap (in small increments) as described in this article :

http://www.autospeed.com/cms/article.html?&A=109878

 

... if that doesn't work either , try to borrow an wideband lambda sensor with a gauge so that you can see what's really happening with the mixture at idle and across the entire rev range and thus you'll be able to adjust the AFM precisely as needed based on the lambda values .

Or try known good spare AFM .

 

D

[scbond 15 1 Cars]

Smoke is white to blueish so oil? There's a slight oil leak coming from the back of the block (not sure what though). It could be that the smoke is unrelated? Normally the car doesn't smoke at all and runs perfect aside from the slight hunting.

 

Already replaced the CTS...was the first thing I tried.

 

The plugs are recently new...I think they were done in January just before I got it. Leads were done as well as vac advance. Not taken the plugs out so may try that tomorrow if I have time.

 

Say I try adjusting the spring tension...to fix the issues I've described would you say go lean on the tension? 8.5 turns out on the mixture screw seems a long way out to me...it only takes 11 ish to unscrew fully. So perhaps the tension was played with, in which case go for over-lean on the tension and then richen slightly with the screw? Say 7 turns out?

 

Which way with the tension do I go to lean the mixture throughout the revs? More tension?

 

Also, tested the AFM with a 9v battery and a bit of wire and the readings for resistance didn't change and I think voltage was all over (I only have a digital multimeter...stupidly the analogue one was cheaper but got the digital because of more settings haha).

 

Greatly appreciate the help buddy.

Edited May 3, 2014 by scbond

[adybatt 1]

hi all, i'm trying to test my AFM, but notice the 944.com site is now down. Does anyone have a copy of the article? or another resource to outline a test procedure? Thanks!

[jackherer 543]

http://web.archive.org/web/20150329103701/http://www.the944.com/afm.htm