G424F(FE) Service Manual
Chapter 5. Engine Management System (EMS)
139
Figure 12. Idle Mixture Adjustment Screw
(with tamper proof cap removed)
Fuel Trim Valve (FTV)
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.
Two FTVs are used to bias the output fuel pressure
on the LPG regulator/converter (N-2007), by
metering air valve vacuum (AVV) into the
atmospheric side of the N-2007 secondary regulator
diaphragm. An orifice balance line connected to the
air inlet side of the mixer provides atmospheric
reference to the N-2007 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 N-2007 maintains fuel flow
at a constant output pressure, due to the calibrated
secondary spring. The amount of fuel flowing from
the N-2007 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 N-2007
secondary diaphragm is referenced to FTV control
pressure while the other side of the diaphragm
reacts to the negative pressure signal from the mixer.
If the pressure on the reference side of the N-2007
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.
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Страница 153: ...G424F FE Service Manual Chapter 5 Engine Management System EMS 151 Figure 22 SECM Wiring Diagram for G424FE LP System ...
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