What determines A/F ratio in a stock S2000? Map sensor or ECU?
05-15-2003, 12:56 PM
#2
Registered User
neither / both.
in closed loop mode, when you're just cruising, the ECU primarily bases the amount of fuel injected on the values reported by the O2 sensor. O2 sensor reads rich, it gives less fuel. O2 sensor reads lean, it gives more fuel. over time it averages out to 14.7:1. the intial values it uses, before corrections based on the O2 sensor, are calculated from a table which primarily relies on MAP and RPM, but also throttle position, vehicle speed, air temperature, coolant temperature, etc.
when you floor it, the O2 sensor becomes useless, and the computer bases the fueling only on the built in tables and a small correction factor learned over time. again, those tables use input from the MAP sensor, the engine speed sensor, the throttle position sensor, etc etc etc.
in closed loop mode, when you're just cruising, the ECU primarily bases the amount of fuel injected on the values reported by the O2 sensor. O2 sensor reads rich, it gives less fuel. O2 sensor reads lean, it gives more fuel. over time it averages out to 14.7:1. the intial values it uses, before corrections based on the O2 sensor, are calculated from a table which primarily relies on MAP and RPM, but also throttle position, vehicle speed, air temperature, coolant temperature, etc.
when you floor it, the O2 sensor becomes useless, and the computer bases the fueling only on the built in tables and a small correction factor learned over time. again, those tables use input from the MAP sensor, the engine speed sensor, the throttle position sensor, etc etc etc.
05-15-2003, 03:18 PM
#4
Registered User
the o2 sensor is in the exhaust system (two of them actually). it measures the oxygen content of the exhaust gas and uses that to determine if the engine is running rich or lean.
the map sensor is in the intake system, and measures the pressure present in the intake manifold. when the throttle is closed, the engine is sucking air out of an almost completely closed chamber, resulting in low (less than atmospheric) pressures. when the throttle is open, air flows freely from the atmosphere into and through the engine, resulting in a manifold pressure near or equal to the atmospheric pressure.
they're totally different sensors... both can break, and the o2 sensor can get fouled over time, resulting in reduced fuel economy because the engine isn't accurately gauging the richness or lean-ness of the exhaust gas. i've never heard of a map sensor getting less accurate over time, although it must be possible.
the map sensor is in the intake system, and measures the pressure present in the intake manifold. when the throttle is closed, the engine is sucking air out of an almost completely closed chamber, resulting in low (less than atmospheric) pressures. when the throttle is open, air flows freely from the atmosphere into and through the engine, resulting in a manifold pressure near or equal to the atmospheric pressure.
they're totally different sensors... both can break, and the o2 sensor can get fouled over time, resulting in reduced fuel economy because the engine isn't accurately gauging the richness or lean-ness of the exhaust gas. i've never heard of a map sensor getting less accurate over time, although it must be possible.
05-15-2003, 03:47 PM
#6
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How good is the OEM O2 sensor?
I heard that it is slowish. Is this true?
Some of the air fuel ratio meter piggy back off this sensor. Does anyone know how good and what how quick the responses these meters are/have?
I heard that it is slowish. Is this true?
Some of the air fuel ratio meter piggy back off this sensor. Does anyone know how good and what how quick the responses these meters are/have?
05-15-2003, 03:59 PM
#7
The MAP sensor is notorious for going haywire; it's one of the oldest known issues for this car. It causes the car's behavior to go haywire, too -- jerking and sputtering with no warning. The common remedy is literally just to tap on it with a screwdriver or something! (Yes, this really works!) You can also order a new one from H&A (board sponsor) but there's no gaurantee the problem won't come back.
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