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Re: air box thermostat[200/1987] posted by Steve on
Monday, 14 September 1998, at 3:31 p.m.
You have it backwards! The thermostat closes the flap and keeps the hot air out. Without it, the flap springs open and hot air gets in all the time, so it will work great in the winter.
If you want to keep hot air out of the intake, leave the thermostat alone and tie the flap closed. You can take the thermostat out, if you want, but it is pointless as long as the flap is tied shut.
I may be wrong, but I don't believe that hot air can burn out the AMM. Here's why: there is an electrical current through the platinum wire which heats it to a constant temperature regardless of the air temperature. If the air is hot, it takes less current to heat the wire, but the temperature of the wire stays the same. The wire is hotter than the air in any case, otherwise the AMM wouldn't work.
Re: air box thermostat[200/1987] posted by Tom Frisardi on
Monday, 14 September 1998, at 3:53 p.m.
I thought that the reason the hot air burned out the AMM was because it fried the electronics, so I would still suspect that a stuck flap could cause an AMM failure.
--Tom Frisardi
Re: air box thermostat[200/1987] posted by Phil on
Monday, 14 September 1998, at 11:41 p.m.
Good point. So if I figured out what size current-limiting resistor to use and soldered that in I should have a wire that never burns out. But don't these things fail electronically from the flap being open all the time and overheating the components???
We may be on to something here men.
Phil
Re: air box thermostat[200/1987] posted by Don Foster on
Tuesday, 15 September 1998, at 7:08 a.m.
Phil --
Maybe I misunderstood what you're proposing..... but substituting a fixed resistor for the hot wire in the AMM won't really work.
The air mass meter is a device called a "hot wire anemometer" (an anemometer is another name for a wind-speed measuring device). In this case, the wire is heated a fixed amount, and the temperature of the wire is measured. The temperature is closely tied to the air velocity past the wire.
(Fixed heating is accomplished by running a fixed current through the wire, and the temperature is inferred by measuring the resistance, which is measured by the resulting voltage drop across the wire.)
You could substitute a resistor for the wire, but the time response of the device would be many seconds -- perhaps minutes -- and your FI system needs millisecond response. The only way to achieve that is with a very low-mass resistor -- hence, the fine wire.
The reason the FI control system goes through the "burn-off" cycle at shutdown is the keep the wire clean -- any carbon, soot, or dust adds insulation (which means errors) and adds to the mass (which means slower response time).
But to follow your other thought.... maybe cooling the AMM electronics with an external airflow is an idea............
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