- Tue Jun 14, 2016 9:07 am
#59066
I am afraid that is the way it is on here sometimes Vil, the original question is soon forgotten hope my answer was of some help.
Sorry, jefrs, but your terminology is slightly off.
"MAP" stands for Manifold Absolute Pressure (and always has). None of them "draw lots of current". Nor are they binary devices, boxerman.
They (at least the ones on our Bullets) provide an analogue output signal which indicates the absolute pressure at that instant. They are called "absolute pressure" because they report the pressure in relation to a vacuum. ("Gauge pressure" is the term for reporting pressure in relation to atmospheric.)
Absolute pressure measurements are important in this role because the sensor can measure the barometric pressure (which it does at the instant of switch-on) as well as the instantaneous manifold pressure whilst the engine is running. The barometric pressure reading is used by the ECU to compensate (primarily) for changes in ambient air pressure at high altitudes - a major requirement that Royal Enfield placed upon Keihin for this system).
So, one sensor does two jobs: it determines barometric pressure at start-up, and also the instantaneous manifold pressure as the engine is running.
MAF stands for Mass Air Flow, and is a totally different beast. Very rarely found on motorcycles for reasons we can discuss if you wish, they measure the mass of air being drawn into the engine. Two types - the hot wire and the hot plate - do draw a lot of current. They use electrical current to warm up a piece of wire (or a plate) placed in the airflow, and then detect the cooling effect of the air flowing past the wire by measuring changes in its electrical resistance. The cooling effect is roughly proportional to the mass of the air flowing past them. Most conductors change their electrical resistance with temperature, so you get a very simple and robust device, with no moving parts, which detects the mass of air flowing into the engine.
From this you can calculate the mass of fuel required and thus inject just the right amount for the desired air:fuel ratio.
I hope that clears up any confusion.
