Triumph TR7 - Air Flow Meter; Engine Speed; Electronic Control of the Fuel Injection System

EMISSION AND EVAPORATIVE LOSS CONTROL SYSTEMS
Electronic Control of the Fuel Injection System
At the heart of the electronic control system is the Electronic
Control Unit
(E.C.U.) which is a box approximately 23 x 18 x
5 ems (9 x 7 x 2 Inches) located beneath a plate on the Iront
passenger footwell (Rover 3500) or under the glove box (TR
models), The E.C.U. receives input signals from various
sensors and computes from these an output signal to the fuel
injector solenoid circuits. When activated the solenoids
'open' the injectors to spray fuel into the engine inlet
manifold, the injectors remaining 'open' for between 1.5 and
10 milliseconds depending on engine running conditions.
The electronic control unit
is sealed, it requires no
maintenance and should
not be opened or tampered with.
Engine Speed
One of the first inputs required by the EG.U. is that of engine
speed and this input
is very simply obtained by taking a
tapping from the ignition coil
low tension circuit output
(negative terminal), Thus the ignition
low tenSion circuit
pulses are passed to the
E.C,U. to be computed into an
engine speed input.
Air Flow Meter
In addition to fuel. the most important input to the engine is
air and the ratio of air to fuel affects both the performance of
the engine and the emission levels of the exhaust gases,
Electronically controlled fuel injection systems
can 'measure'
the air used
by the engine In one of two ways. by air pressure
or
by air flow. The air flow alternative IS used on these
models.
12
Fig. 13 Electronic control unit
Continued