m10 afm testing?

[dmjensen]

Anyone have the procedure for testing the afm on an 85 m10?
I can't seem to find it online and I currently don't have access to alldata.


PS. Don't buy a chilton, they're worthless.

[thebutterson]

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

I used a 9v battery and multimeter with some clamping leads to test mine.

[Gregs///M]

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

I used a 9v battery and multimeter with some clamping leads to test mine.

I truly feel bad for all the thousands of guys throughout the many years who read and reference this article about AFM's. Unfortunately, the author who wrote it was wrong about many things including the testing procedure and requirements.

I've also seen several other websites follow this same path. In my opinion, the "the944" article is just plain incorrect. I'll summarize briefly:

1. There are two generations of AFM's. I believe 1986 might be the cut off year between older and newer. The older require a 12v input voltage and does not need to be regulated.
However, the later generation requires a highly regulated 5v input voltage.

The 9v battery trick would work on the older 12v type units but will not work on the 5v AFM units past 1986. These AFM's require regulated 5V for a reason, using a 9V is far beyond its intended voltage input and can lead to inaccuracies and substrate damage.

2. You CANNOT test these with a digital volt/multi meter. Despite what the many thousands of "techs" will tell you, this is plain wrong. Digital meters calculate its voltage reading through a process of averaging over time. Therefore, when you are "testing" with a DMM, you are viewing an average result.

The only way to truly test an AFM is with an oscilloscope. You must read the voltage output over time and inspect that plot. No averaging can be incorporated into your results.

For example...Here is a shot of my testing of a BAD AFM.


If you were to measure this signal with a DMM, you would see an average of the voltage up and down. However, the oscilloscope will capture these brief voltage drops throughout its feedback range. These voltage drops occur in milliseconds that a DMM will never capture.

Voltage drops like in the picture would give you a symptom of misfire but it is your ECM thinking your car is at rest when its really travelling, thus severely retarding the fuel output by the fuel injectors.

Hope that clears things up! BTW, you may might more info on my thread...
http://www.r3vlimited.com/board/showthread.php?t=247831