Propane EFI System
24
24 690 32 Rev. AKohlerEngines.com
Oxygen sensor functions like a small battery, generating
a voltage signal to ECU based upon difference in oxygen
content between exhaust gas and ambient air.
Tip of sensor, protruding into exhaust gas, is hollow.
Outer portion of tip is surrounded by exhaust gas, with
inner portion exposed to ambient air. When oxygen
concentration on one side of tip is different than that of
other side, a voltage signal up to 1.0 volt is generated
and sent to ECU. Voltage signal tells ECU if engine is
straying from ideal fuel mixture, and ECU then adjusts
injector pulse accordingly.
Oxygen sensor functions after being heated to a
minimum of 400°C (752°F). A heater inside sensor heats
electrode to optimum temperature in about 10 seconds.
Oxygen sensor receives ground through wire, eliminating
need for proper grounding through muffl er. If problems
indicate a bad oxygen sensor, check all connections and
wire harness. Oxygen sensor can also be contaminated
by leaded fuel, certain RTV and/or other silicone
compounds, fuel injector cleaners, etc. Use only those
products indicated as O2 Sensor Safe.
Manifold absolute pressure (MAP) sensor provides
immediate manifold pressure information to ECU.
MAP measures difference in pressure between outside
atmosphere and vacuum level inside intake manifold
and monitors pressure in manifold as primary means
of detecting load. Data is used to calculate air density
and determine engine's mass air fl ow rate, which in
turn determines required ideal fueling. MAP also stores
instant barometric pressure reading when key is turned
ON.
Fuel injectors mount into intake manifold, and high
pressure fuel line attaches to them at top end.
Replaceable O-rings on both ends of injector prevent
external fuel leakage and also insulate it from heat and
vibration. A special clip connects each injector to high
pressure fuel line and holds it in place. O-rings and
retaining clip must be replaced any time fuel injector is
separated from its normal mounting position.
When key switch is on, lock-off valve will open briefl y
and allow fuel into system at 24-26 psi, and voltage is
present at injector. At proper instant, ECU completes
ground circuit, energizing injector. Valve needle in
injector is opened electromagnetically, and pressure in
high pressure fuel line forces fuel down through inside.
Director plate at tip of injector contains a series of
calibrated openings which directs fuel into manifold.
Injectors have sequential fueling that open and close
once every other crankshaft revolution. Amount of fuel
injected is controlled by ECU and determined by length
of time valve needle is held open, also referred to as
injection duration or pulse width. Time injector is open
(milliseconds) may vary in duration depending on speed
and load requirements of engine.
A high-voltage, solid-state, battery ignition system is
used with EFI system. ECU controls ignition output and
timing through transistorized control of primary current
delivered to coils. Based on input from crankshaft
position sensor, ECU determines correct fi ring point
for speed at which engine is running. At proper instant,
it interrupts fl ow of primary current in coil, causing
electromagnetic fl ux fi eld to collapse. Flux collapse
induces an instantaneous high voltage in coil secondary
which is strong enough to bridge gap on spark plug.
Each coil fi res every other revolution.
EFI engines are equipped with either a 20 or 25 amp
charging system to accommodate combined electrical
demands of ignition system and specifi c application.
Charging system troubleshooting information is provided
in Electrical System.
When key switch is turned ON and all safety switch
requirements are met, ECU activates lock-off valve for
about six seconds, which pressurizes system for start-
up. If key switch is not promptly turned to start position,
engine fails to start, or engine is stopped with key
switch ON (as in case of an accident), ECU switches off
lock-off valve preventing continued delivery of fuel. In
this situation, MIL will go on, but it will go back off after
4 cranking revolutions if system function is OK. Once
engine is running, lock-off valve remains on.
There are two fi lters in system, one on inlet of vaporizer/
regulator will be a 30-micron button fi lter, and one after
will be a special metal 10-micron fi lter. Be sure to use
metal propane 10-micron fi lter for replacement.
High pressure fuel line is an assembly of hoses, injector
caps and a fuel connector to vaporizer/regulator. High
pressure fuel line feeds fuel to top of injectors through
injector caps. Caps are fastened to intake manifold and
injectors are locked into place. A small retaining clip
provides a secondary lock.
High pressure fuel line is serviced as a complete
assembly to prevent tampering and safety hazards.
Components are not individually serviceable.
Vacuum hose connects vaporizer/regulator to throttle
body, compensating regulated pressure for air cleaner
condition.
EFI engines have no carburetor, so throttle function
(regulate incoming combustion airfl ow) is achieved with
a throttle valve in a separate throttle body attached to
intake manifold. Throttle body/intake manifold provides
mounting for fuel injectors, throttle position sensor, MAP
sensor, intake air temperature sensor, high pressure fuel
line, idle speed screw, and air cleaner assembly.
Idle speed is only adjustment that may be performed on
EFI system. Standard idle speed setting for EFI engines
is 1500 RPM, but certain applications might require
a different setting. Check equipment manufacturer’s
recommendation.
For starting and warm up, ECU will adjust fuel and
ignition timing, based upon ambient temperature, engine
temperature, and loads present. In cold conditions,
idle speed will probably be different than normal for a
few moments. Under other conditions, idle speed may
actually start lower than normal, but gradually increase
to established setting as operation continues. Do not
attempt to circumvent this warm up period, or readjust
idle speed during this time. Engine must be completely
warmed up, in closed loop operating mode for accurate
idle adjustment.
To Next Page
Loading...
