Illustration 1 demonstrates the relationship between the parts of the system.
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| Illustration 1 | g00818126 |
Schematic of the electronic ignition system and related components (1) Remote control panel (status) (2) Engine mounted junction box (3) Engine speed/timing sensor (4) Manifold air pressure sensor (5) Detonation sensor (6) EIS control module (7) DDT (8) Ignition transformer (9) Spark plug | |
EIS control module (6) is mounted on the engine. The EIS control module must be programmed for the installation in order to properly control the ignition. DDT (7) is used to program the EIS control module. The DDT can be connected to remote control panel (1) or junction box (2) .
Note: For information on the programmable parameters, refer to Systems Operation, "Electronic Control System Parameters". For information on the monitoring system, refer to Systems Operation, "Engine Monitoring System".
Two switches have an effect on the ignition system: the engine control switch and the switch for fuel selection.
When the engine control switch on remote control panel (1) is switched to the manual start position, the EIS control module begins operating the ignition system.
If the switch for fuel selection is in the natural gas position, the EIS control module will use the desired timing that is programmed. If the switch for fuel selection is in the propane position, the EIS control module retards the timing by ten degrees.
The EIS control module uses engine speed/timing sensor (3), manifold air pressure sensor (4), and detonation sensors (5) to monitor engine operation. The EIS control module determines the optimum ignition timing for the engine operation and the module initiates the timed ignition via ignition transformers (8) and spark plug (9) .
Information from the EIS control module is sent to engine mounted junction box (2) and the remote control panel. If a problem with the electronic system is detected, a diagnostic code is generated. The diagnostic code can be monitored with the remote control panel or with the DDT.
The EIS control module has several internal components that perform different functions. The components and the functions are listed in Table 1.
| Internal Components and Functions of the EIS Control Module | |
| Component | Function |
| Ignition control | Receive input from the engine control switch, the switch for fuel selection, and the DDT. |
| Provide information on engine status and diagnostics to electronic service tools. | |
| Provide desired timing and voltage to the ignition transformers' control. | |
| Receive input from the interpreters and the filter. | |
| Ignition transformers' control | Receive input from the ignition control. |
| Provide voltage to the transformers. | |
| Provide input to the interpreter of diagnostics for the transformers. | |
| Interpreter of diagnostics for the transformers | Receive input from the ignition transformers' control. |
| Provide input to the ignition control. | |
| Interpreter for the signal from the engine speed/timing sensor | Receive input from the engine speed/timing sensor. |
| Provide input to the ignition control. | |
| Interpreter for the signal from the manifold air pressure sensor | Receive input from the manifold air pressure sensor. |
| Provide input to the ignition control. | |
| Filter for the detonation sensors | Receive input from the detonation sensors. |
| Provide input to the ignition control. | |
The relationships of the EIS control module, the sensors, and the transformers are described below.
Engine Speed/Timing Sensor
The engine speed/timing sensor provides information about engine speed and the position of the crankshaft to the EIS control module.
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| Illustration 2 | g00818359 |
(1) Engine speed/timing sensor | |
A timing wheel is mounted in front of the governor drive. Engine speed/timing sensor (1) is installed in the cover. A magnetic pickup is located in the plastic sliphead of the sensor. The EIS control module supplies approximately 13 VDC to the sensor. As the teeth of the timing wheel rotate past the sliphead of the sensor, the sensor generates a signal that matches the pattern of the teeth. The signal is sent to an interpreter for the EIS control module.
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| Illustration 3 | g00807464 |
Engine speed/timing sensor and timing wheel | |
The timing wheel has a special tooth pattern that indicates the position of the camshaft and the direction of rotation. The timing wheel has 24 slots in the outer diameter. Twenty-one of the slots are narrow. Three of the slots are about 2.5 times wider than the rest of the slots. When the engine rotates in the normal direction, the slots pass the engine speed/timing sensor in the following order:
- 1 wide slot
- 3 narrow slots
- 2 wide slots
- 18 narrow slots
The number one cylinder is at the top center position when the edge of the first narrow slot passes the center of the sliphead. All 24 teeth pass the sliphead during one revolution of the camshaft or two revolutions of the crankshaft.
With information from the engine speed/timing sensor, the EIS control module is able to calculate the positions of the pistons in the cylinders. According to the ignition timing that is selected, the EIS control module sends voltage pulses to the transformers for firing of the spark plugs.
The engine speed/timing sensor also monitors engine speed. If a speed sensitive timing map is selected, the EIS control module adjusts the ignition timing according to the engine rpm.
The EIS control module will shut down the engine if problems with the engine speed/timing sensor's electrical circuit are detected. The corresponding diagnostic code is generated.
Manifold Air Pressure Sensor
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| Illustration 4 | g00818361 |
Manifold air pressure sensor | |
The EIS control module supplies approximately 13 VDC to the manifold air pressure sensor. The sensor monitors the absolute inlet manifold air pressure. The sensor sends a signal to the EIS control module. The EIS control module has an interpreter that uses the signal to calculate the engine load. If a timing map that is sensitive to load is selected, the EIS control module adjusts the ignition timing according to the calculated load.
The EIS control module will generate a diagnostic code if problems with the manifold air pressure sensor's electrical circuit are detected.
Detonation Sensors
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| Illustration 5 | g00818362 |
Detonation sensor's buffer module | |
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| Illustration 6 | g00818378 |
(1) Buffer module (2) Accelerometer | |
A detonation sensor consists of buffer module (1), accelerometer (2), and wiring. A detonation sensor is located on the upper cylinder block on each side of the engine. Each sensor monitors one bank of cylinders. The EIS control module supplies approximately 13 VDC to the sensors.
The detonation sensors provide an electrical signal of the mechanical engine vibrations to the EIS control module. The accelerometers provide electrical signals to the buffer modules. The buffers provide a signal with an offset of approximately 6 VDC to a filter in the EIS control module. The signal indicates mechanical engine vibrations. The frequency of the signal corresponds to the mechanical frequency of the vibrations. The amplitude of the signal is proportional to the intensity of the vibrations.
The EIS control module monitors the signals in order to determine the presence and the severity of detonation. The EIS control module retards the timing in order to limit detonation levels.
The retardation of timing is the first level of protection against detonation. The EIS control module can retard timing by as few as 0.1 degrees for light detonation levels. The timing can be retarded up to six degrees for severe detonation.
As the detonation level decreases, the EIS control module will begin to advance the timing out of the detonation retarded timing. The advance is proportional to the level of detonation. The rate is faster for lighter detonation. The fastest rate of advance is two degrees per minute.
Engine shutdown is the second level of protection against detonation. If retardation of the timing is unsuccessful and the detonation continues at severe levels, the EIS control module will signal for an engine shutdown.
Protection from detonation is enabled under the following conditions:
- The inlet manifold air pressure reaches an absolute pressure of 110 kPa (16 psi).
- If a diagnostic code is generated for the manifold air pressure sensor, protection from detonation is enabled regardless of the inlet manifold air pressure.
Protection from detonation is disabled under the following conditions:
- The inlet manifold air pressure reaches an absolute pressure of less than 110 kPa (16 psi).
- The engine speed is less than 500 rpm.
The EIS control module will generate a diagnostic code if a problem with the electrical circuit for the detonation sensors is detected.
Ignition Transformers
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| Illustration 7 | g00735979 |
(1) Ignition transformer (2) Spark plug (3) Valve cover (4) MS connector (5) EIS control module | |
Each cylinder has an ignition transformer that is located under the valve cover. Each transformer has a primary circuit and a secondary circuit.
To initiate combustion in a cylinder, the EIS control module sends a pulse of approximately 190 volts to the primary coil of the ignition transformer. The transformer increases the voltage to a range between 8000 and 32,000 volts. The high voltage creates a spark across the spark plug electrode.
The transformers are grounded through the valve covers. Use caution when a valve cover is removed.
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Ignition systems can cause electrical shocks. Avoid contacting the ignition system components and wiring. Do not attempt to remove the valve covers when the engine is operating. The transformers are grounded to the valve covers. Personal injury or death may result and the ignition system will be damaged if the valve covers are removed during engine operation. The engine will not operate without the valve covers. |
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Always disconnect the ignition harness from the transformer when a valve cover is removed.
The ignition harness is routed inside the engine to an MS connector on the valve cover. Another wiring harness connects the transformers to the EIS control module.
The EIS control module monitors the ignition system. The EIS control module will generate a diagnostic code if problems with the electrical circuit are detected.