50 Fuel System Troubleshooting TP-6903 5/16a
3.4. Hard Start
Definition: The engine cranks but does not start for a
long time. The engine does eventually run, or may start
but immediately stalls.
Figure 3-6 Hard Start Troubleshooting
Checks Action
Preliminary Checks
Make sure the engine’s operator is using the correct starting procedure.
Sensor Checks
Check the coolant temperature sensor with Spectrum. Compare the engine coolant
temperature with the ambient air temperature on a cold engine. If the coolant
temperature reading is more than 10 degrees greater or less than the ambient air
temperature on a cold engine, check for high resistance in the coolant sensor circuit.
Check the crankshaft position sensor.
Check the electronic throttle connections.
Fuel System Checks
Note: A partially closed fuel supply valve will create an extended crank or no start
condition.
Check the air-fuel mixer assembly for proper installation and leakage.
o Verify proper operation of the fuel shut-off solenoid valves.
o Verify proper operation of the system fuel pressure regulator.
o Check for air intake system leakage between the air-fuel mixer, throttle body and air
filter assembly. Check the fuel system pressures.
Ignition System Checks
Note: Natural Gas and Liquefied Petroleum Gas require higher secondary ignition system
voltages than the equivalent gasoline operating conditions.
Check for the proper ignition voltage output.
Verify that the spark plugs are the correct type and properly gapped.
Check the spark plugs for the following conditions:
o Wet plugs (oil fouling).
o Cracks.
o Wear.
o Burned electrodes.
o Heavy deposits.
Check for bare or shorted ignition leads.
Check for loose ignition coil connections.
If the engine starts but then immediately stalls, check the crankshaft position sensor.
Check for improper gap, debris or faulty connections.
Engine Mechanical Checks
Check for the following:
o Engine vacuum leaks.
o Manifold vacuum leaks.
o Charge air cooler leaks on turbocharged engines.
o Mixer vacuum leaks.
o Improper valve timing.
o Low compression.
o Improper valve clearance.
o Worn rocker arms.
o Broken or weak valve springs.
o Worn camshaft lobes.
Exhaust System Checks
Check the exhaust system for a possible restriction:
o Inspect the exhaust system for damaged or collapsed pipes.
o Inspect the muffler for signs of heat distress or for possible internal failure.
Check that the turbocharger turbine and compressor blades do not rub or bind against
the turbocharger housing.
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