JLG 400S Service And Maintenance Manual page 207

Checks
Intermittent Malfunction Indicator Lamp
(MIL)
Loss of DTC Memory
Additional Checks
DEFINITION: The engine cranks OK, but does not start.
Preliminary Checks
Control Module Checks
Sensor Checks
Fuel System Checks
Ignition System Checks
Engine Mechanical Checks
3121671
Table 3-14. GM Engine Symptom Diagnosis
The following components can cause intermittent MIL and no DTC(s):
² A defective relay, Control Module driven solenoid, or a switch that can cause electrical system interference. Normally, the problem will occur
when the faulty component is operating.
² The improper installation of electrical devices, such as lights, 2-way radios, electric motors, etc.
² The ignition secondary voltage shorted to a ground.
² The Malfunction Indicator Lamp (MIL) circuit or the Diagnostic Test Terminal intermittently shorted to ground.
² The Control Module grounds.
To check for the loss of the DTC Memory:
1. Disconnect the TMAP sensor.
2. Idle the engine until the Malfunction Indicator Lamp illuminates.
The ECM should store a TMAP DTC. The TMAP DTC should remain in the memory when the ignition is turned OFF. If the TMAP DTC does not store
and remain, the ECM is faulty
Refer to Important Preliminary Checks.
If a scan tool is available:
² Check for proper communication with both the ECM
² Check the fuse in the ECM battery power circuit. Refer to Engine Controls Schematics.
² Check battery power, ignition power and ground circuits to the ECM. Refer to Engine Control Schematics. Verify voltage and/or continuity for
each circuit.
² Check the TMAP sensor.
² Check the Magnetic pickup sensor (RPM).
Important: A closed LPG manual fuel shut off valve will create a no start condition.
² Check for air intake system leakage between the mixer and the throttle body.
² Verify proper operation of the low pressure lock-off solenoids.
² Check the fuel system pressures. Refer to the LPG Fuel System Diagnosis.
² Check for proper mixer air valve operation.
Note: LPG being a gaseous fuel requires higher secondary ignition system voltages for the equivalent gasoline operating conditions.
² Check for the proper ignition voltage output with J 26792 or the equivalent.
² Verify that the spark plugs are correct for use with LPG (R42LTS)
² Check the spark plugs for the following conditions:
- Wet plugs
- Cracks
- Wear
- Improper gap
- Burned electrodes
- Heavy deposits
² Check for bare or shorted ignition wires.
² Check for loose ignition coil connections at the coil.
Important: The LPG Fuel system works on a fumigation principle of fuel introduction and is more sensitive to intake manifold leakage than
the gasoline fuel supply system.
² Check for the following:
- Vacuum leaks
- Improper valve timing
- Low compression
- Bent pushrods
- Worn rocker arms
- Broken or weak valve springs
- Worn camshaft lobes.
SECTION 3 - CHASSIS & TURNTABLE
Action
No Start
3-149