Isuzu 4ja1, Workshop Manual

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Engine Control System (4JH1) 6E-249
Checks Action
Fuel System Checks
Inspect the fuel system for the following conditions. Refer to the Fuel System section.
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Inspect for water contamination in the fuel.
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Inspect for external fuel leaks or fuel leakage into the engine oil.
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Inspect the fuel lines between the fuel tank and fuel injection pump for tightness and
all fuel hoses for cuts, cracks and for the use of proper clamps.
Notice: The fuel system from the fuel tank(s) to the fuel injection pump is under a
slight vacuum with the engine running. As a result, air can enter the fuel system if
these connections are not tight. Air in the fuel system will cause fuel injection pump
internal pressure fluctuations especially at high engine speed and load.
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Inspect for air in the fuel system.
Notice: If many air bubbles appear in the fuel, check the fuel system line connections
between the fuel tank and the fuel injection pump for tightness and all fuel hoses for
cuts, cracks and for the use of proper clamps.
a. Remove the fuel hose that connects to the fuel injection pump suction side.
b. Substitute a clear hose.
Notice: A hose must be cleaned.
c. Connect the clear hose to the fuel injection pump.
d. Bleed the fuel system.
e. Let the engine run at idle for at least 2 minutes.
f. Accelerator the engine between idle and W.O.T. (accelerator pedal full travel) many
times while observing the clear hose.
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Inspect the fuel tank vent hose for a plugged or kinked.
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Inspect inside the fuel tank for any foreign material that may be getting drawn into
the fuel line pickup causing a blocked condition. Draw fuel from the fuel tank at the
fuel line (as close to the fuel tank as possible) going to the fuel pickup tube to verify a
clean stream of fuel comes out (use the hand-held vacuum pump 5-8840-0279-0/J-
23738-A with a clear hose or equivalent). This will ensure the fuel pickup tube is not
cracked drawing air into the fuel line.
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Inspect the fuel injection pump operation.
Notice: The fuel injection pump must be timed to the engine.
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Inspect the eye bolt for a
ny type of restriction or collapsed gauze filter.
Notice: If any type of restriction found, check for a condition that causes contaminated
fuel, such as the customer is using an aftermarket fuel filter or extended maintenance
interval. Also inspect fuel waxing or icing that is caused by an incorrect fuel type used
in winter season or water intrusion in the fuel system.
Inspect the fuel injection nozzle(s) for proper splay condition or operating pressure.
Notice: Only first stage of operating pressure can be checked.
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Inspect the timing device operating correctly. Observe the Actual Injection Timing
parameter with the scan tool while running the engine. The Actual Injection Timing
parameter must follow the Desired Injection Timing within 2°CA on each engine
speed. Engine idle > around 2000 RPM> around 3000 RPM. If not, inspect the fuel
system restriction, air in the fuel or fuel injection pump operation.
Air Intake System Checks
Inspect the air intake system for the following conditions.
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Inspect the air cleaner and air intake ducts for a restriction, holes, or leaks.
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Inspect for a restriction or leak in the intercooler.
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Inspect for a restriction in the turbocharger inlet duct.
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Inspect for a restriction or deposit in the intake throttle bore.
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Inspect for a restriction or leak in the intake manifold.
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Inspect for a restriction or damage at MAF sensor.
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Inspect for a worn or damaged turbocharger turbine wheel, shaft or compressor
wheel. Refer to turbocharger inspection in the Engine Mechanical section.
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Inspect for turbocharger wastegate valve operation. Refer to wastegate valve
inspection in the Engine Mechanical section.
Exhaust System Checks
Inspect the exhaust system for a possible restriction. Refer to the Exhaust System
section.
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Inspect for a restriction in the catalytic converter or exhaust pipes.