VIN L
Fuel System Diagnosis - High Pressure Side
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.
Circuit/System Description
The high pressure fuel pump is located at the front of the engine valley and is engine driven by the camshaft gear. Fuel is drawn by the fuel supply pump from the primary fuel tank and delivered through the diesel fuel conditioning module to the high pressure pump. The engine control module (ECM) controls the fuel rail pressure using two pulse width modulated fuel rail pressure regulators. Fuel pressure regulator 1 is located on the fuel injection pump and meters the amount of fuel that enters the high pressure side of the pump. From the high pressure pump, the fuel moves to the two fuel rails through a high pressure metal line. The fuel rails distributes high pressure fuel to all 8 fuel injectors. The ECM varies the pulse width modulated voltage to the fuel pressure regulator 2 to relieve excessive fuel pressure which returns to the fuel tank. When the ignition is OFF, fuel pressure regulator 2 opens to bleed off the pressure in the fuel rail.
The ECM commands fuel pressure regulator 2 to control fuel pressure at idle and commands fuel pressure regulator 1 to control fuel pressure when engine speeds are above 1700 RPM. Under certain conditions both regulators are used to control fuel pressure. The actual and desired fuel pressures should be within 690 kPa (100 psi) during all engine operating modes.
Diagnostic Aids
* Contaminated fuel or incorrect fuel may cause erratic fuel pressure.
* A low fuel condition may cause driveability concerns.
* Water or contaminated fuel may cause driveability concerns. Refer to Contaminants-in-Fuel Diagnosis (Contaminants-in-Fuel Diagnosis).
* When ambient temperatures are below 0°C (32°F), the fuel tank pickup screen may be iced over from water in the fuel tank.
* High fuel injector return flow may cause fuel pressure control concerns.
* The addition of fuel system enhancements, such as auxiliary fuel tanks or add on fuel filters may relate to driveability complaints.
Reference Information
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information.
Special Tools
* CH-48027 Digital Pressure Gauge
* CH-50375 Fuel Injector Return Line Adaptor
Circuit/System Verification
Note:
* If you were not referred to this test from another diagnostic, do not perform this procedure.
* Only perform this test when the fuel temperature is warmer than 18°C (65°F).
Engine cranking, observe that the Actual Fuel Rail Pressure and the Desired Fuel Rail Pressure are within 690 kPa (100 psi).
Circuit/System Testing
1. Ignition OFF, verify there are no external leaks or damage to the fuel return and supply lines.
• If a condition is found, refer to Fuel Leak Diagnosis (Fuel Leak Diagnosis) for further diagnosis.
2. Install the CH-48027 to the fuel rail service port. Engine cranking or idling, verify that the CH-48027 displays between 1-6 in Hg vacuum.
• If greater than the specified range, inspect for a restricted fuel filter, kinked, or restricted fuel supply lines. Refer to Fuel System Diagnosis (Fuel System Diagnosis) for further diagnosis.
3. Install the CH-50375 with a gauge to a fuel injector return line.
4. Engine cranking or idling, verify the injector return line pressure is greater than 3 bar (43 psi).
• If less then the specified range, refer to Fuel Return System Diagnosis (Fuel Return System Diagnosis) for further diagnosis.
5. Remove the fuel pressure regulator 2 return hose and plug the hose to prevent fuel leakage.
6. Install a section of rubber fuel hose on the fuel pressure regulator 2 outlet and place the loose end of hose into a clean fuel container.
7. Perform the applicable test listed below:
Cranking Test - Engine No Start
1. Engine cranking for 15 seconds.
2. Observe the volume of fuel from fuel pressure regulator 2. The volume of fuel should be less than 10 ml (0.4 oz).
• If greater than the specified value, replace the Q45B fuel pressure regulator 2.
3. Disconnect the harness connector at the fuel pressure regulator 2 and crank the engine for 15 second.
• If no return volume, replace the G18 high pressure fuel pump.
Engine Running Test - Engine Starts
Note: Measure only the amount of fuel that leaks after the engine has reached 1800 RPM.
1. Engine idling, increase engine speed to 1800 RPM for 15 seconds.
2. Observe the volume of fuel from fuel pressure regulator 2. The volume of fuel should be less than 10 ml (0.4 oz).
• If greater than the specified value, replace the Q45B fuel pressure regulator 2.
8. Install the fuel pressure regulator 2 return line.
Note: This procedure must be performed at idle and at 1800 RPM.
9. Command the fuel pressure incrementally through the entire fuel pressure range with a scan tool. The Actual Fuel Rail Pressure and the Desired Fuel Rail Pressure should be within 690 kPa (100 psi) for the entire fuel pressure range.
• If the desired and actual fuel pressure at idle is within 690 kPa (100 psi) and was not within 690 kPa (100 psi) at 1800 RPM, replace the Q45A fuel pressure regulator 1.
• If the desired and actual fuel pressure at idle was not within 690 kPa (100 psi) but was within 690 kPa (100 psi) at 1800 RPM, replace the Q45B fuel pressure regulator 2.
• If the desired and actual fuel pressure was not within 690 kPa (100 psi) at idle and at 1800 RPM, replace the G18 high pressure fuel pump.
10. If all the components test normal, test the fuel injector return flow. Refer to Fuel Injector Diagnosis (Fuel Injector Diagnosis). If the fuel injectors test normal, replace the G18 high pressure fuel pump.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the repair.
* Fuel Injection Pump Replacement (Fuel Injection Pump Replacement)
* Fuel Pressure Regulator Replacement (Service and Repair)
* Fuel Pressure Relief Valve Replacement (Service and Repair)