When to replace AFM in 87 3.2L
 

The car in question is a 1987 Carrera Widebody Targa with 85K miles. I have been told by two different places now that the car feels down on power. One well respected shop wants to replace the AFM, but can't tell me for sure that is the problem.

Is the AFM a maintenance part that needs to be replaced every so often? How do I know when it is bad?

Tracy Meyer

How did they reach the conclusion. It is rare to see an AFM go bad, most of the time there is just wear on the wiper track on the potentiometer. Check out this site to see what I am talking about and how to do a DIY refurbish: http://www.frwilk.com/944dme/afm.htm

I'd do a compression check first. Then I would check to make sure the throttle is adjusted properly and the WOT micro switch is engaging (a large percentage don't). The AFM's are expensive to just buy cause you think it may be a problem.

I agree with Kurt. I adjusted mine and it made a huge improvement in throttle response.

Just keep the mechanicals CLEAN and lubed (frequently, for me), inspecting the mentioned traces and their wear. Last time thru, I went "anal" on the device. Since I already had my scope out,.. looking at signals, here and there,..I decided to take the AFM apart and give her her normal go-over. Clean, lube, inspect every last bit of soldering THE MEASURE! As with ANY measurement of critical resistive component, this is one of the few times I love to use my my old analog (and I mean tube!) meter to watch that LONG needle move everso smoothly while sweeping the arm across the resistive trace,..EASILY seeing any points of disturbing anomolies. THIS TIME, I put the scope on it to watch (and actually quantify, with high resolution) the noise and easily see (the "signatures" of the events. Interesting.......As anyone one surmise, clean, clean copper is a very good thing,...at anytime...I cleaned mine very well,..eliminating many of these "minor spots" on the trace....results are simply a smoother to and fro'...........surely, quicker, a bit. I had a friend who moved his wiper arm. We had talked before about this,..I shared with him all I've read here at the P-University,..and my experiences/protocols...

Never went by his place to assist,...but he always laughed at my freakiness with anything "tube"...... He changed out his AFM because he claims to have seen several "glitches" on his DMM while sweeping the pot. Turns out, he's seeing (on his Fluke DMM) the autoranging changeover on the display ranges, mistaking them for "bad resistive spots" at points on the copper trace. After explaining to him (this DMM trait on HIS meter), I took that AFM to my bench and she's even cleaner than mine, particularly: on the scope.......

No one here would make this flawed observation, for not knowing your test equipment's characteristics and misreading the testing results...on the other hand, there are MANY newbie DIYs out there,...meter in-hand,..ready to engage a problem,..and THAT's cool,..especially with their experience here..........hell,....I've only owned this beast for almost two years,...accomplished much with it (at a DD level),..but when I delve into the engine forum (and here, even), I'm often humbled at what I really have (yet) to learn about these engines

However, and over to simplicity,...as MANY of us have already experienced, discovery of something impeding WOT (WOT switch aside), was one helluva' wake-up for me..I'll never forget that fix, ensuring the cable wasn't binding somewhere along the path......GEEEEZE....

I've not yet seen a measurement (or condition) on my car that would warrant movement of the wiper arm towards fresh copper, but it is sure good to know that it can easily be done when the time comes...

Best,

Doyle

Thanks, guys, for all the suggestions. I will pull out the AFM and give it a good look this weekend. I bet I find the traces are either dirty or worn. It looks like I have a rebuilt one installed already. This should not be too difficult. I will use my trusty DMM (on fixed scaled of course) to see how it sweeps.

Tracy Meyer

Before I would pull the AFM I would make sure you have a recent tune up and make sure your throttle is opening completely. The 3.2 engines tend to get the throttle linkage out of adjustment and only allow the throttle to open part of the way.

While you're in there, you might as well make some adjustments to see if it helps.

Tightening the spring is equivalent to increasing control pressure in a CIS system and moving the pointer would be the same as turning the mixture screw. Just make sure you pencil in a mark where you started so you don't get lost.

Have fun.