Fuel System Diagnosis
Fuel System Diagnosis
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 fuel injection pump has a low pressure pump that draws fuel from the tank and through the fuel sender assembly and fuel lines to the fuel conditioning module. The fuel conditioning module consists of a fuel filter, water in fuel sensor, fuel filter pressure switch and a hand primer. Fuel is drawn through the fuel conditioning module to supply the high pressure side of the fuel injection pump. The low pressure side of the fuel injection pump also supplies the exhaust aftertreatment fuel injector and the fuel injector return system, with 4 bar (58 psi) of pressure. Excess fuel is returned back to the fuel tank or the conditioning module. Fuel that is returned to the conditioning module helps to heat the fuel going to the fuel injection pump.
This diagnostic is used to test the low pressure fuel supply to the fuel injection pump.
Diagnostic Aids
* An Engine Cranks but Will Not Run or Hard Start symptom may exist if air is being drawn into the fuel injection system due to the following conditions:
- Deformed or cut O-rings at the fuel supply line connections
- Improperly seated fuel supply line fittings
- Porous or weathered rubber fuel supply lines
- Fuel filter vent screw not tighten or cross threaded
- Fuel filter not tightened properly
- Leaking or damaged fuel filter pressure switch
* Contaminated or improper fuel may cause drivability or starting issues. Refer to Fuel System Specifications [1][2]Fuel Delivery and Air Induction and Contaminants-in-Fuel Diagnosis Contaminants-in-Fuel Diagnosis.
* A leaking fuel injector return line constant pressure regulator may cause No-Start, Hard Start, or Stall conditions.
Reference Information
Description and Operation
Fuel System Description Fuel System Description
Scan Tool Reference
Control Module References Control Module References for scan tool information
Special Tools
* CH-48027 Digital Pressure Gauge
* EN-47969 Fuel Supply Diagnostic Hose
* J-23738-A MityVac
* J 44581 Fuel Line Disconnect Tool
Circuit/System Verification
1. Inspect the fuel system for damage or external leaks before proceeding.
2. Verify that adequate fuel is in the fuel tank before proceeding.
3. Observe the Actual Fuel Rail Pressure parameter with a scan tool. During engine cranking, the pressure should be at least 10 MPa (1450 psi). With the engine running at idle the pressure should be close to the Desired Fuel Rail Pressure. As the engine speed increase, the Desired Fuel Rail Pressure and the Actual Fuel Rail Pressure should be within 2 MPa (290 psi) of each other.
4. Verify the fuel filter pressure switch parameter does not display restricted.
Circuit/System Testing
Note: You must perform the Circuit/System Verification before proceeding with Circuit/System Testing
1. Install the CH-48027 to the fuel system service port near the front of the engine.
2. Disconnect the harness connector at the B181 fuel filter pressure switch.
3. Prime the fuel system until 68 kPa (10 psi) is indicated on the CH-48027 . Fuel pressure should not drop below 13.7 kPa (2 psi) in less than 1 minute.
• Repair any leaks or replace any components found to be damaged or leaking.
• If less than 68 kPa (10 psi) is indicated and no leaks are present, test the fuel supply lines for restrictions, damage or leakage. If the lines test normal, replace the fuel sender assembly.
4. Disconnect the fuel supply line at the engine. Refer to Metal Collar Quick Connect Fitting Service Service and Repair.
5. Cap off the fuel supply pipe on the engine side with a rubber plug and a clamp.
6. Engine cranking, verify the CH-48027 displays greater the 10 in. Hg of vacuum.
• If vacuum is present during cranking but bleeds off rapidly, repair the leak in the fuel supply line.
• If less than the specified value, replace the G18 high pressure fuel pump.
Note: Changes in engine speed can cause an increase of air bubbles that enter the EN-47969 . An air pocket at the top of the EN-47969 loop is considered a normal condition.
7. Remove the rubber plug from the fuel supply line and install the EN-47969 . Create a vertical loop in the hose to observe the incoming fuel for air bubbles. Prime the fuel system until all air has been purged. Start and run the engine for at least 10 minutes to allow the fuel system to stabilize. Engine at idle, observe the fuel entering the EN-47969 for air bubbles.
• If air bubbles were observed entering the transparent hose, test the fuel feed lines and sender for leaks.
• If no air bubbles are present , remove the EN-47969 and run the engine to ensure no fuel leaks exist.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
* Engine Fuel Vacuum Switch Replacement Engine Fuel Vacuum Switch Replacement
* Fuel Injection Pump Replacement Fuel Injection Pump Replacement
* Fuel Sender Assembly Replacement Service and Repair