Service manual

G420F(FE) Service Manual Chapter 5. Engine Management System (EMS) 169
Branch-Tee Fitting
A branch-tee fitting is installed in the atmospheric
vent port of the N-2007 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 FTVs are open AVV is
sent to the atmospheric side of the N-2007
secondary diaphragm, which lowers the reference
pressure, closing the N-2007 secondary valve and
leaning the air/fuel mixture. The MI-07 system is
calibrated to run rich without the FTV. By modulating
(pulsing) the FTVs the SECM can control the
amount of AVV applied to the N-2007 secondary
diaphragm. Increasing the amount of time the FTVs
remain open (modulation or duty cycle) causes the
air/fuel mixture to become leaner; decreasing the
modulation (duty cycle) enriches the mixture.
Figure 13. Fuel Trim Valves Connected to MI-07 System