MI-04 LP Fuel Filter After exiting the fuel tank, liquid propane passes through a serviceable inline fuel filter to the electric fuel lock off. (Figure 11) shows a typical inline type LP fuel filter manufactured by Century. The primary function of the fuel filter is to remove particles and sediments that have found their way into the tank. The LP fuel filter will not remove heavy end solids and paraffin’s that build up in LPG fuel systems as a result of vaporization.
MI-04 Fuel Lock-Off (Electric) The fuel lock-off is a safety shutoff valve, normally held closed by spring pressure, which is operated by an electric solenoid and prevents fuel flow to the regulator/converter when the engine is not in operation. This is the first of three safety locks in the MI-04 system. (Figure 12) shows the electric fuel lock assembly. In the MI-04 design, power is supplied to the fuel lock-off with the SECM controlling the lock-off ground (earth) connection.
The lock-off remains in a normally closed (NC) position until the key switch is activated, this supplies power to the lock-off and the SECM but will not open the lock-off until the SECM provides the lock-off ground connection. This design gives the SECM full control of the lock-off while providing additional safety by closing the fuel lock-off in the unlikely event of a power failure, wiring failure or module failure. When the liquid service valve in the fuel container is opened liquid propane flows through the LP filter and through the service line to the fuel lock-off.
Liquid propane enters the lock-off through the ј” NPT liquid inlet port and stops with the lock-off in the normally closed position. When the engine is cranked over the main power relay applies power to the lock-off and the SECM provides the lock-off ground causing current to flow through the windings of the solenoid creating a magnetic field. The strength of this magnetic field is sufficient to lift the lock-off valve off of its seat against spring pressure. When the valve is open liquid propane, at tank pressure, flows through the lock-off outlet to the pressure regulator/converter. A stall safety shutoff feature is built into the SECM to close the lock-off in case of a stall condition.
The SECM monitors three engine states. Crank, when the VR sensor detects any engine revolutions. Stall, when the key is in the ON position but the VR sensor detects no engine revolutions, and the Run state, when the engine reaches pre-idle RPM. When an operator turns on the key switch the lock-off is opened but if the operator fails to crank the engine, the SECM will close the lock-off after 5 seconds. Figure 11 Figure 12 G420E/G424E Tier LP Engine System Operational Overview 17