Gm Lpg Fuel System Diagnosis - JLG 400S Service And Maintenance Manual

SECTION 3 - CHASSIS & TURNTABLE
STEP
1 Were you referred to this procedure by a DTC diagnostic chart?
2 Perform the On Board Diagnostic (OBD) System Check.
Are any DTCs present in the ECM?
3 Verify that the LPG fuel tank has a minimum of 1/4 tank of fuel, that the manual valve is open
and the tank quick connect is fully engaged
Does the vehicle have fuel?
4 1. Connect a water column gauge or a manometer to the secondary test port of the low pressure
regulator (LPR).
2. Start the engine and allow it to reach operating temperature.
Does the engine start and run?
5 With the engine idling, observe the pressure reading for the LPR secondary pressure.
Does the fuel pressure fluctuate rhythmically OUTSIDE the specified range?
6 1. Disconnect the EPR electrical connectors. NOTE: This action will cause a DTC to be set by the
ECM
2. With the engine idling observe the pressure reading on the secondary test port.
Is the fuel pressure WITHIN the specified range?
7 1. Inspect the air intake stream between the mixer assembly and the throttle body for leaks.
2. Inspect the fuel hose connection between the LPR and mixer assembly for damage or leak-
age.
3. Inspect any vacuum hoses for leaks
Was a problem found and corrected?
8 1. Connect a water column gauge or a manometer to the secondary test port of the low pressure
regulator (LPR).
2. Crank the engine and observe the pressure reading for the LPR secondary pressure.
Does the fuel pressure indicate a vacuum is present?
9 1. Remove Air induction hose to the mixer
2. Observe the air valve for movement while the engine is cranking. Note: Movement of the air
valve will be minimal at cranking speeds.
Does the air valve move when the engine is cranked?
10 1. Inspect the air intake stream to the mixer assembly and the throttle body for vacuum leaks.
2. Inspect the vacuum hoses from the mixer for proper connection and condition.
Was a problem found and repaired?
11 Inspect the fuel hose connection between the LPR and the mixer assembly for damage or leak-
age.
Was a problem found and repaired?
12 1. Connect a 0-10 psi gauge to the primary test port of the low pressure regulator (LPR).
2. Crank the engine and observe the pressure reading for the LPR primary pressure.
Is the fuel pressure ABOVE the specified value?
13 1. Turn OFF the ignition.
2. Disconnect the LPL connector.
3. Install a test light between the pins of the LPL connector.
4. Crank the engine. The test light should illuminate.
Does the test light illuminate?
14 Using a DVOM, check the resistance of the low pressure lock-off (LPL).
Is the resistance within the specified range?
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Table 3-13. GM LPG Fuel System Diagnosis
ACTION VALUE(S) YES
- - Go to Step 3
- - Go to the
applicable DTC Table
- - Go to Step 4
- - Go to Step 5
-1.0" to Go to Step 25
-2.0" w.c
-1.0" to Go to Fuel Control System
-2.0" w.c Diagnosis
- - Go to Step 26
- - Go to Step 12
- - Go to Step 11
- - Go to Step 26
- - Go to Step 26
1- 3 PSI Go to Step 22
- - Go to Step 14
12W - 16W Go to Step 15
NO
Go to Step 2
Go to Step 3
- -
Go to Step 8
Go to Step 6
Go to Step 7
Go to Step 22
Go to Step 9
Go to Step 10
Go to Step 24
Go to Step 12
Go to Step 13
Go to Step 16
Go to Step 23
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