Re: EFI Pieces and parts
I believe it to be a good idea to explain the components, their function, and finally, how all of the items work together.
Maybe list the components used as either input devices or output devices.
Defining the different EFI systems, N alpha, Speed Density, and Mass Air Flow.
N alpha - uses two input sensors for fuel calculation, tachometer reference and throttle position. Very crude system for the radical engine. Its table (fuel map or program) has to be manually changed to adjust output device, the fuel injector(s).
Speed Density - a control system having multiple input sensors with a few output devices. A simple(?) fuel management system.
Input sensors include:
MAP (Manifold Absolute Pressure) measures intake manifold pressure;
TPS (Throttle Position Sensor) as JimM said, gives ECM the amount, read as a %, of throttle opening;
CTS (coolant temperature sensor) tells the ECM how cold/hot the engine coolant is;
Tachometer reference - taken from the ignition system to tell the ECM engine rpm;
MAT (Manifold Air Tempersture) - tells ECM the temp of incoming air;
FTS (Fuel Temperature Sensor) - tells ECM temp of fuel, some systems have this, some don't;
O2 sensor (Oxygen sensor) - a device in the exhaust telling the ECM how much oxygen is in the exhaust gases, some are single wire and installed in the exh manifold, others have heaters to heat them up and are installed in the exhaust piping;
And there are more eluding me at the moment.
Oil Pressure sensor - tells ECM oil is being pumped.
Knock sensor - tells ECM of detonation and pinging.
Output devices are:
IAC ( Idle Air Control) - as JimM said, a stepper motor driving a pintle in/out of as hole to control idle speed, a controlled vacuum leak. Has two drivers from the ECM , one for forwards and one for backwards;
EGR (Exhaust Gas Recirculation) - a system used to control the combustion temperature by re-routing exhaust gas through the intake system to dilute the intake charge and reduce emissions. The valve itself, in earlier designs, used solenoid controlled vacuum to pull open the valve. Newer valves are stepper motor driven and give feedback to the ECM as to the amount open;
Cannister purge - a solenoid on the purge line of the charcoal cannister to open the the tank and pull the vapors from the tank and burn them.
Injector pulse - a solenoid with a needle & seat to control fuel flow by input signal given from the ECM after the ECM has "looked" at all input sensors and read the fuel map/program. The injector has two wires, one wire with a relay controlled fused battery voltage, the other wire is ECM controlled. If both wires read high, close to battery, then injector is closed, ECM decides to open injector, ECM places a low, i.e., 0.5 vdc, on the wire. Now, a difference in potential or voltage is present and injector opens.
Ignition timing - retards/advances timing as instructed by ECM dependent upon input sensors.
Mass Air Flow - same as Speed Density, except has a MAF (Mass Air Flow meter) is used to tell the ECM how much air the engine is ingesting. Some designs are spring loaded doors with a wiper arm on a rheostat, others are hot wire design. Hot wire meter is a length of wire and the ECM runs current through this wire to keep it hot. As more air travels across the wire the wire cools, ECM adds more current to keep it warm. This change of current tells the ECM the amount of air being injesting and this info is used to adjust injector pulse. MAF sensor also tells ECM temp of incoming air. When ECM is turned off, as in ignition OFF, the wire is superheated to clean itself by burning off any foreign material collected, as in bugs on the grill.
In all the input sensors to the ECM, one lead to the sensor is ECM ground. This ground is not vehicle nor battery ground, but a low potential of voltage, less than 0.5 VDC.
The MAP sensor, Manifold Absolute Pressure, and TPS, Throttle Position Sensor, have an ECM ground lead and in the case of the TPS, the technician uses the ECM ground lead to adjust for idle voltage rather than using vehicle ground.
Sorry to get carried away. I'm sure I've left out some good info. The above info is referenced for OBD I systems and from what I have read from books & mags and from School Of Hard Knocks. I'm sure everyone has attended this school.
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