Service manual

G420F(FE) Service Manual Chapter 6. LPG FUEL DELIVERY SYSTEM 215
Field Adjustment Procedure:
The idle mixture adjustment should only be
necessary on a new mixer that does not have the
tamper proof cap installed. The method for making
the idle mixture adjustment to a running engine is to
use the Service Tool software by connecting a
laptop computer to the SECM. If you do not have the
Service Tool a multimeter capable of measuring
duty cycle, such as a Fluke 87 III, can be used. If
using a multimeter, connect the meter positive lead
to between battery positive and the meter negative
to the FTV signal wire. For the Fluke 87, press the
“RANGE” button until 4 or 40 appears in the lower
right-hand corner of the display. Press the “Hz”
button twice so that the percent sign (%) appears on
the right-hand side of the display. The multimeter
will then read the duty cycle percentage the same as
the Service Tool shown in Figure 41.
1. After installing a new mixer, operate the engine
Bon LPG fuel. Start the engine and permit it to
warm up until the coolant temperature (ECT on
Mototune display) is approximately 167°F (75 oC).
2. Place the transmission in Neutral.
3. Mototune display parameter LP Fuel Control must
display “Closed Loop”.
4. Use the Mototune Service Tool to monitor Duty
Cycle % on the Mototune display.
5. To adjust the idle mixture screw, use a hex or
Allen-type wrench. Turning the screw in
(clockwise) should increase the duty cycle; turning
the screw out (counterclockwise) should decrease
the duty cycle.
6. Adjust the idle mixture screw on the mixer until a
reading of 35-55% is reached for the FTV Duty
Cycle in Closed Loop Idle (Figure 41). If engine
idle performance is unstable screw the idle screw
in slightly to see if stability is obtained, but in no
case should duty cycle exceed 60%.
7. Use the accelerator pedal to increase rpm above
idle momentarily (rev the engine) then release the
pedal to return to idle rpm. The duty cycle setting
should remain within the adjustment range (35-
55%). Place your thumb over the adjustment port
for a more accurate reading by preventing air from
leaking past the mixture adjustment screw, which
may cause the duty cycle to decrease.
8. If the FTV duty cycle reading is above 55% adjust
the idle adjustment screw outward and re-check
the duty cycle reading. Continue to do this until
the FTV duty cycle reading is within the optimum
range (35-55%). DO NOT adjust the screw so far
outward that the tamper proof cap cannot be
installed. A duty cycle measurement at Closed
Loop Idle of 25-60% is acceptable if the optimum
range of 35-55% cannot be reached through
adjustment. If the FTV duty cycle cannot be
adjusted below 60%, the mixer is faulty and
should be replaced.
NOTE : If the FTV Duty Cycle reading is NOT
between 25-60%, check for possible vacuum leaks,
manifold leaks, or a faulty mixer.
9. Turn the ignition key to the OFF position to shut
down the engine.
10. Install the tamper proof cap on the idle mixture
screw adjustment port using a large pin punch,
so that no further adjustments can be made
(Figure 42).