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New Style AMM

posted by  B.B. on  Tue Apr 22 20:56 CST 2025
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last visit: Mon Oct 6 13:15 CST 2014
[RELATED]

There's some replacement AMMs for RWD that use a thermistor
instead of a heated platinum wire.
A review at Swedish auto parts says its a good substitute.
The review indicates that a messed up AMM can cause the engine to run rich.
My car runs rich with black soot around the new stainless exhaust pipe and ratty gas mileage.
I just replaced the old O2 sensor and wonder about my old AMM.

Another site that rehabs old AMM's says that they calibrate them perhaps using
a trim pot in the AMM.

I have a pair of old AMM's with the 4 small steel phillips head screws for the cover solidly frozen into metal casting.
Months soak with penetrating oil doesn't work, and you can't put heat because the cover is plastic. Can these be re-calibrated? Then I can drill out the screws and have at it and jury rig the cover back on.
I can't find any info other than some resistance values at the connector.

Does anyone have info on the circuit board hidden under that cover, and info to
adjust the AMM. Or is it a waste of time, and better to buy a thermistor AMM?

Thanks, Bill








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    New Style AMM

    posted by  Will740turbo on  Fri May 23 00:11 CST 2025
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    last visit: Wed Oct 22 16:09 CST 2014
    [RELATED]

    A standard AMM uses a thermistor plus a hot-wire. The platinum wire that does the "burn-off" when the ignition is shut off is a heating element.

    Basically, it has 2 wires - one hot wire and one thermistor. The hot-wire transfers more heat to the thermistor when there is less airflow and less when there is more airflow.

    The trim pot on old LH2.2 (or 2.0?) AMMs was used with the O2 sensor output to tune mixture. I don't believe there are ANY adjustable components inside the AMMs, but you could have the thing repaired for probably a few hundred dollars by an electronics shop like Direct Repair Labs in Beaverton, OR.







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