A 2020 Sierra 2500 Duramax with 40,000 miles experienced a front-end collision requiring significant repairs, including a new frame. After repairs, the truck ran briefly but developed performance issues and eventually stalled. Troubleshooting revealed communication issues within the LAN system, potentially caused by the glow plug module. After resolving this, the truck ran poorly and stalled again. The current issue involves a P0016 code (crankshaft/camshaft position correlation), high fuel rail pressure (8500 psi at idle), low oil pressure (7-8 psi when warm), and cylinders #6 and #8 not responding to injector cutoff tests.
Diagnosing the Duramax’s High Fuel Pressure Problem
The owner replaced the cam and crank sensors, camshaft gear, and reluctor ring, ensuring proper timing marks. The high-pressure fuel pump is generating excessive pressure, reaching 8500 psi at idle and 1200 RPM before the engine stalls. Normal idle pressure for an L5P Duramax is significantly lower, around 4000-5000 psi. The excessive pressure points towards a potential issue with the fuel pressure regulation system.
The owner confirmed a normal low-side fuel pressure of 60 psi and ruled out fuel line restrictions by inspecting and replacing the left fuel rail, which houses the L5p Fuel Pressure Regulator 2. Despite this, the high fuel pressure persists. This suggests the new regulator might be faulty or another component is contributing to the problem.
Possible Causes and Solutions for the High Fuel Pressure
Several potential issues could be causing the high fuel pressure and related problems:
1. Faulty Fuel Pressure Regulator (FPR):
Even though a new L5P fuel pressure regulator 2 was installed, it could still be defective. Testing the regulator using a scan tool to command different fuel pressures can help determine its functionality.
2. Fuel Rail Pressure Sensor (FRPS) Malfunction:
A faulty FRPS could be providing incorrect readings to the Engine Control Module (ECM), leading to improper fuel pressure regulation. Testing or replacing the FRPS is recommended.
3. ECM Issues:
The ECM controls the FPR and relies on data from the FRPS. A software glitch or internal fault within the ECM could cause it to command excessive fuel pressure. Checking for ECM updates or potential damage is necessary.
4. Wiring Harness Problems:
Damaged or corroded wiring in the fuel system harness, especially to the FPR and FRPS, can disrupt communication and lead to malfunctions. Thoroughly inspecting the harness for damage is crucial.
Addressing the Low Oil Pressure and Injector Issues
The low oil pressure (7-8 psi when warm) is alarming and could indicate serious engine damage. While fuel dilution might contribute, the problem persisted after an oil change. Possible causes include a faulty oil pump, worn bearings, or internal engine damage resulting from the initial collision.
The unresponsive injectors (#6 and #8) might be related to the high fuel pressure overwhelming them or could indicate individual injector failures. Swapping injectors with functioning cylinders can help isolate the problem.
Conclusion and Next Steps
The combination of high fuel pressure, low oil pressure, and unresponsive injectors suggests complex issues within the fuel and lubrication systems of this Duramax. A systematic diagnostic approach, focusing on verifying the functionality of the L5P fuel pressure regulator 2, FRPS, ECM, and wiring harness, is crucial. Further investigation into the low oil pressure is paramount, as it could indicate significant engine damage. Addressing these underlying problems is necessary before attempting to drive the truck again to prevent further damage. Consulting a qualified diesel mechanic with experience in L5P Duramax engines is highly recommended.
