MI-04 Fuel Trim Valve The Fuel Trim Valve (FTV) is a two-way electric solenoid valve and is controlled by a pulse width modulated (PWM) signal provided by the SECM. The FTV is used to bias the output fuel pressure on the LPG regulator/converter (N-2001), by metering air valve vacuum (AVV) into the atmospheric side of the N-2001 secondary regulator diaphragm. An orifice balance line connected to the air inlet side of the mixer provides atmospheric reference to the N-2001 when the FTV is closed. The SECM uses feedback voltage from the O2 sensor to determine the amount of bias needed to the regulator/converter.
In normal operation the N2001 maintains fuel flow at a constant output pressure, due to the calibrated secondary spring. The amount of fuel flowing from the N2001 will vary depending on how far the secondary diaphragm opens the secondary valve in response to the negative pressure signal generated by the air/fuel mixer. One side of the N2001 secondary diaphragm is referenced to atmospheric pressure while the other side of the diaphragm reacts to the negative pressure signal from the mixer.
If the pressure on the atmospheric side of the N2001 secondary diaphragm is reduced, the diaphragm will close the secondary valve until a balance condition exists across the diaphragm, reducing fuel flow and leaning the air/fuel mixture. A branch-tee fitting is installed in the atmospheric vent port of the N2001 with one side of the branch-tee connected to the intake side of the mixer forming the balance line and referencing atmospheric pressure. The other side of the branch-tee fitting connects to the FTV inlet (small housing side). The FTV outlet (large housing connector side) connects to the AVV port.
When the FTV is open AVV is sent to the atmospheric side of the N2001 secondary diaphragm, which lowers the reference pressure, closing the N2001 secondary valve and leaning the air/fuel mixture. The MI-04 system is calibrated to run rich without the FTV. By modulating (pulsing) the FTV the SECM can control the amount of AVV applied to the N2001 secondary diaphragm. Increasing the amount of times the FTV opens (modulation or duty cycle) causes the air/fuel mixture to become leaner; decreasing the modulation (duty cycle) enriches the mixture. (Figure 22) shows the Fuel Trim Valve connected in the MI-04 system.
Fuel Trim Valve Balance Line FTV Figure 22 G420E/G424E Tier LP Engine System Operational Overview 23