Impco HHI, Service Manual

Page: 30 / 485

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LPG FUEL SYSTEM DIAGNOSIS
The Electronic Pressure Regulator Assembly (EPR), Shown with Port Fittings and Shut-off Valve.
FUEL SYSTEM DESCRIPTION
The Engine Control Module (ECM) receives in-
formation from various engine sensors in order
to control the operation of the Electronic Pres-
sure Regulator (EPR) and Shut-Off Valve. The
Shut-Off Valve solenoid prevents fuel
flow u n-
less the engine is cranking or running.
LPG is stored in the tank as a liquid and deli-
vered under pressure of up to 21.5 BAR (312
psi). At Key ON, the EPR receives a two (2)
second prime pulse from the ECM, allowing
time for the LPG to
flow from the tank through
the fuel filter and fuel lines to the EPR. Inside of
the EPR, fuel is vaporized and reduced in pres-
sure in two stages. The
first stage reduces the
tank pressure to approximately 20.68 kilopas-
cals (3.0 psi). The second stage then reduces
the pressure to approximately negative 38.1
mm (1.5” of water column) when vacuum from
the engine draws in fuel.
The fuel is then drawn in from the secondary
chamber of the EPR by the vacuum generated
by air
flowing through the M ixer. This vacuum
is also generates lift for the mixer air valve and
is commonly referred to as air valve vacuum.
Once in the mixer, the fuel is combined with air
and is drawn into the engine for combustion.
DIAGNOSTIC AIDS
This procedure is intended to diagnose a ve-
hicle operating on LPG. If the vehicle will not
continue to run on LPG, refer to Hard Start for
preliminary checks. Before starting
this proce-
dure, complete the following tasks to verify that
liquid fuel is being delivered to the EPR:

Inspect fuel tank to verify it has a sufficient
amount of fuel.

Verify manual shut off valve on the LPG
tank is fully opened.

Verify that the excess flow valve has not
been activated.

Inspect fuel tank to ensure it is properly
mounted and rotated to the correct position.

Inspect the hoses leading from the tank en-
suring they are properly connected and do
not have any kinks or damage.