Ignition Control; Ignition Timing Control; Ignition And Combustion Order; Ignition Timing - TOHATSU MFS 25D Service Manual

Fuel System (Fuel Injection)

(2) Ignition Control

The ECU's microcomputer is pre-programmed with optimal ignition timings according to the condition of the engine.
The ECU obtains information about the engine operating status such as the revolution speed, throttle opening,
manifold pressure (air intake vacuum pressure), cooling water temperature etc. based on the signals from the above-
mentioned sensors to ignite the fuel at the optimal ignition timing.

1) Ignition Timing Control

Ignition timing control is classified into two types, the first type by correcting the ignition timing during normal
operation, and the second type by fixing the ignition advance angle (at engine startup or when an error occurs). In
either case, ECU corrects ignition time or fixes it to the base.
• The basic ignition timing is determined by the engine revolution speed and manifold pressure (intake air vacuum
pressure).
• Signals that are used for correction of ignition timing includes cooling water temperature, manifold intake air
temperature, change of pressure at acceleration/deceleration under atmospheric pressure, and engine revolution
speed.
• Ignition timing is fixed to the base at acceleration, deceleration, when high speed ESG is on, low speed ESG is on,
or when hydraulic pressure is reduced.

2) Ignition and Combustion Order

No. of Ignitions: Once per revolution of each cylinder (around the end of the compression and exhaust strokes)
Ignition sequence: #1
Combustion sequence: #1

3) Ignition Timing

The ignition timing is set as described below.
Model
MFS25D
MFS30D

4) Operations

• At Engine Starting and During Warm-up
Ignition timing is fixed at BTDC5° at engine startup.
The input signal and the engine temperature, manifold intake air temperature, engine speed and atmospheric
pressure, on the basis of the programs stored in the ECU, the microcomputer determines the ignition timing after
starting.
• During idling and low speed running
When the ECU receives the manifold pressure (intake air vacuum pressure) signal and input signal from the pulser
coil (engine revolution speed signal), it controls the ignition timing so that the idling and low speed revolution
speeds stabilize.
• During normal operation
Microcomputer determines ignition timing in accordance with ECU's program by using cooling water temperature,
manifold intake air temperature, atmospheric pressure and engine revolution speed as input signals. The maximum
advance angle during normal operation is as shown below. MFS25D: BTDC24°, MFS30D: BTDC28°
• During acceleration/Deceleration
When engine revolution speed changes much and is reduced below (or exceed) a setting value, ECU determines
that engine is accelerating (or decelerating), and microcomputer determines the ignition timing based on the
program installed in ECU.
• During engine over-revolution
When the engine revolution speed exceeds the maximum allowable value (MFS25D: 6200 min
6700 min (rpm)), the ECU stops feeding fuel to control the revolution based on pulser coil signals. This is the state
-1
that engine high speed ESG is "ON".
• Engine low speed ESG is "ON".
When any of the following state has been detected, engine revolution speed is controlled to 2,800r/min to prevent or
reduce engine damage. This is the state that engine low speed ESG is "ON".
• Engine is overheating.: The engine temperature sensor detects 95°C or higher.
• Engine hydraulic pressure is low.: Oil pressure switch is ON (40 kPa (5.8 psi) [0.4 kg/cm
4-26
#2 #3 #1 #2 #3
#3 #2 #1 (for every 240° of the crank angle)
Range of Ignition Angle
ATDC3°- BTDC24°
ATDC3°- BTDC28°
#1 (for every 120° of the crank angle)
Engine Starting
BTDC5°
BTDC5°
Idling
ATDC3°
ATDC3°
(rpm), MFS30D:
-1
] or less) is detected.
2
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