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How does an S4 AFM actually work?

Old 07-10-19, 01:09 PM
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How does an S4 AFM actually work?

So I'm having a bit of a problem with the afm and keeping the car running( 86 gxl with standalone fuel pump circuit) but that is not my question, there is enough info on that already!

My question is how does the signal from the afm actually work, i originally thought it worked like a potentiometer, but that isn't the case. I know its supposed to stay within 50-500 ohms the entire gate distance but they don't gradually increase like a potentiometer, the ohm value jumps around a lot.

Any info on this would be greatly appreciated!
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Old 07-10-19, 01:51 PM
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it would probably be easier to measure voltage, its around 2.5v at idle, and i think maxes out at 0v or 5v (i don't recall)
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Old 07-11-19, 06:04 PM
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I used this procedure a few years ago. I can't vouch for it's validity, other than to say that my AFM tested fine and seems to operate normally. Hopefully it's of used to you.

Link here, see the final post
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