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24 690 31 Rev. D
KohlerEngines.com
Propane EFI System
WARNING
Explosive Fuel can cause fi res and severe
burns.
If a gaseous odor is detected, ventilate area
and contact an authorized service technician.
Propane is extremely fl ammable and is heavier than air
and tends to settle in low areas where a spark or fl ame
could ignite gas. Do not start or operate this engine
in a poorly ventilated area where leaking gas could
accumulate and endanger safety of persons in area.
To ensure personal safety, installation and repair of
propane fuel supply systems must be performed only
by qualifi ed propane system technicians. Improperly
installed and maintained propane equipment could
cause fuel supply system or other components to
malfunction, causing gas leaks.
Observe federal, state and local laws governing
propane fuel, storage, and systems.
Typical propane electronic fuel injection (EFI) system
and related components include:
● Vaporizer/regulator.
● Fuel fi lter.
● High pressure fuel line.
● Fuel line(s).
● Gaseous propane fuel injectors.
● Throttle body/intake manifold.
● Electronic control unit (ECU).
● Ignition coils.
● Engine (oil) temperature sensor.
● Throttle position sensor (TPS). Earlier engines have a
contacting (brushes) TPS. Later engines have a
contactless (magnetic) TPS.
● Crankshaft position sensor.
● Oxygen sensor.
● Earlier engines have a separate manifold absolute
pressure sensor (MAP) and an intake air temperature
(IAT) sensor (located in throttle body).
● Later engines have a combined temperature/manifold
absolute pressure (TMAP) sensor.
● Wire harness assembly & affi liated wiring.
● Malfunction indicator light (MIL) - optional.
FUEL RECOMMENDATIONS
Refer to Maintenance.
FUEL LINE
High pressure fuel line meeting a minimum of SAE
R7 standard must be installed on Kohler Co. engines
equipped with propane EFI system (from vaporizer/
regulator to injectors).
OPERATION
NOTE: When performing voltage or continuity tests,
avoid putting excessive pressure on or against
connector pins. Flat pin probes are
recommended for testing to avoid spreading or
bending terminals.
EFI system is designed to provide peak engine
performance with optimum fuel effi ciency and lowest
possible emissions. Ignition and injection functions
are electronically controlled, monitored and continually
corrected during operation to maintain ideal air/fuel ratio.
Central component of system is Electronic Control Unit
(ECU) which manages system operation, determining
best combination of fuel mixture and ignition timing for
current operating conditions.
Fuel is delivered from tank to integrated lock-off valve at
tank pressure. Fuel travels to vaporizer/regulator which
reduces pressure to 24-26 psi (typical). Fuel then passes
through a fi ne high pressure fi lter, is delivered from
vaporizer/regulator through high pressure fuel line into
injectors, which inject fuel into intake ports. ECU controls
amount of fuel by varying length of time that injectors
are on. This can range from 2 to over 12 milliseconds
depending on fuel requirements. Controlled injection of
fuel occurs every other crankshaft revolution, or once for
each 4-stroke cycle. When intake valve opens, air/fuel
mixture is drawn into combustion chamber, compressed,
ignited, and burned.
ECU controls amount of fuel being injected and ignition
timing by monitoring primary sensor signals for engine
temperature, speed (RPM), and throttle position (load).
These primary signals are compared to preprogrammed
maps in ECU computer chip, and ECU adjusts fuel
delivery to match mapped values. After engine reaches
operating temperature, an exhaust gas oxygen sensor
provides feedback to ECU based upon amount of
unused oxygen in exhaust, indicating whether fuel
mixture being delivered is rich or lean. Based upon this
feedback, ECU further adjusts fuel input to re-establish
ideal air/fuel ratio. This operating mode is referred to as
closed loop operation. EFI system operates closed loop
when all three of following conditions are met:
● Oil temperature is greater than 50-60°C (122-140°F).
● Oxygen sensor has warmed suffi ciently to provide a
signal (minimum 400°C, 752°F).
● Engine operation is at a steady state (not starting,
warming up, accelerating, etc.).
During closed loop operation ECU has ability to readjust
temporary and learned adaptive controls, providing
compensation for changes in overall engine condition
and operating environment, so it will be able to maintain
ideal air/fuel ratio. This system requires a minimum
engine oil temperature greater than 60-70°C (140-158°F)
to properly adapt. These adaptive values are maintained
as long as ECU is not reset.
During certain operating periods such as cold starts,
warm up, acceleration, high load, etc., a richer air/fuel
ratio is required and system operates in an open loop
mode. In open loop operation oxygen sensor output is
used to ensure engine is running rich, and controlling
adjustments are based on primary sensor signals and
programmed maps only. This system operates open
loop whenever three conditions for closed loop operation
(above) are not being met.
ECU is brain or central processing computer of entire
EFI system. During operation, sensors continuously
gather data which is relayed through wiring harness
to input circuits within ECU. Signals to ECU include:
ignition (on/off ), crankshaft position and speed (RPM),
throttle position, oil temperature, intake air temperature,
exhaust oxygen levels, manifold absolute pressure, and
battery voltage.
