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Measures air flow - more Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Fri, 29 Apr 2005 07:52:50
In Reply to: Air Mass Meter.... What does it do???, Jello4j, Fri, 29 Apr 2005 07:13:46 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The air mass meter measures the airflow into the engine. To be exact, it meausre the air mass. Why? So the engine control can tell how much fuel to inject. When you press the gas pedal, you don't control fuel - you simply open a valve to let more air in. The engine control decides how much fuel to inject based on the airflow.
The AMM works by heating a special wire very hot - anywhere between 100 and 155 degrees C, depending on AMM model number. As air flows over the wire, it cools the wire down. The AMM circuitry adds current to keep the wire at the same temperature. So the more air flowing over the wire, the more current required to keep it at temperature. And since the amount of heat air can pull away depends on its mass, it actually measures air mass.
Since gunk and oil can be in the air, after you shut the car off, the AMM heats the wire to 1000deg C to burn off any gunk. It's call, surprisingly enough, "Burn off".
How can you tell the AMM is working? If it isn't working at all, you'll get a Check Engine light, idle will be lousy, and it will seem like the gas pedal has no effect.
If the AMM is getting old and creaky, as they do with age, the idle will be lumpy, and and you'll get off-idle hesitation - when you go to pull away from a light, the gas pedal will seem to ignore you until you really get into it.
Beyond that, you can do some voltage checks, but the best approach is to swap in a known good AMM. Please Note - all AMMs look quite a lot alike, but they are not all interchangeable. ALWAYS replace ONLY with the same part number.
posted by 192.249....
, Fri, 29 Apr 2005 07:52:50 <-- Viewing This Message
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