900 L4-1985cc 2.0L SOHC (1988)
Speed Relay (Turbo Only): Description and Operation
Fig. 31 Speed Relay Terminal ID
Speed governed fuel boosting takes place at engine speeds above 4600 RPM. The pulse ratio was either 85% or 92%.
At engine speeds above 4600 RPM and before the throttle butterfly has passed the 72° position, there is a signal from terminal 1 in the throttle position
sensor to terminal 31A in the speed relay, Fig. 31. Therefore, terminal 7 in the ECU is grounded via terminal 87 in the relay, and terminal 31 in the
speed relay is grounded via terminal 31 in the time relay, resulting in a pulse ratio of 85% being selected.
If the throttle butterfly passes the 72° position, the circuit to terminal 31A in the speed relay is broken, terminal 11 in the ECU is grounded via
terminal 3 in the throttle position sensor, terminal TK in the AC relay and terminal 11 in the time relay, resulting in a pulse ratio of 92%.
Pressure governed fuel boosting is used in addition to the speed governed fuel boosting and the boosting governed by the throttle position sensor.
A pressure switch is connected in parallel with the speed relay and is used to sense the pressure in the intake manifold. When the pressure is between
3.6 and 4.4 psi (0.25 and 0.30 bar), the pressure switch closes, grounding ECU pin 7 and providing fuel boosting with a pulse ratio of 85%.
