Fuel Pressure Maintenance For 2006 Duramax Engines

The fuel rail pressure on a 2006 Duramax is a very common issue and can leave you stranded if not addressed. The fuel rail pressure runs at 6000-26,000 psi on the high side and the low side runs under vacuum as the injection pump sucks the fuel from the tank. The deviation between commanded rail pressure can be well known by the driver at wide-open throttle (WOT) or when the truck is under load. However, it may go unnoticed under light operation. Any consistent deviation between commanded and actual fuel rail pressure that is more than 1,500 PSI should be addressed immediately.

Fuel rail pressure issues

A vehicle's fuel system comprises at least four components: the fuel pump, fuel pressure sensor, fuel rail, and the ECU, which monitors everything. The fuel pressure should be as per the manufacturer's recommendations; otherwise, the engine will not function properly.

Symptoms of Low Fuel Pressure

• Unresponsive throttle or a stalling engine
• Difficulty starting the car
• Check engine light on the dashboard
• Misfires
• Low performance

Causes of Low Fuel Pressure

• Clogged fuel filter
• Bad fuel pump
• Bad fuel pressure regulator
• Stuck fuel injector
• Bad fuel pipe line
• Faulty fuel pressure sensor

Diagnosis and Repair

To diagnose a fuel pressure issue, you will need to scan for additional codes, visually inspect the fuel system components, measure the fuel pressure at the rail, and test the fuel pumps and pressure sensor.

The repair will depend on the specific issue. For example, if the fuel filter is clogged, it will need to be replaced. If there is a problem with the fuel pump, you will need to confirm that it is getting power and ground, and if so, replace it. If the pressure regulator is faulty, it will need to be replaced.

Fuel Rail Pressure Testing

To test the fuel pressure, you will need a fuel pressure gauge and a few other parts to attach it to the rail. You will then need to find the correct fuel pressure specifications for your car model and check if the fuel pressure matches the specifications.

A 2006 GMC Sierra 2500 with a Duramax engine was reported to be going into limp mode after about 20 miles of driving. The issue was diagnosed as low fuel rail pressure, with error codes P0087 and P0401. The owner changed the fuel filter every 3,000 miles and performed regular service. The solution was to replace the fuel feed line, which was collapsing under suction from the fuel pump.

Low power or engine power reduction

• Clogged fuel filter: This is one of the most frequently reported causes of reduced engine power. It is recommended to replace the fuel filter and use high-quality fuel from reputable stations.
• Throttle position sensor (TPS): A faulty TPS can affect the engine's performance and trigger the "reduced engine power" message.
• Mass Air Flow (MAF) sensor: A faulty MAF sensor can lead to reduced engine power and the P0101 trouble code.
• Coolant issues: Low coolant levels or an air lock in the cooling system can trigger the "reduced engine power" message.
• Exhaust Gas Recirculation (EGR) valve: Problems with the EGR valve or related systems can cause reduced engine power.
• Fuel supply lines: The rubber fuel supply line can collapse over time, leading to low fuel pressure and the P0087 code.
• Glow plugs: If the glow plugs are faulty, the engine may have difficulty starting, especially in cold conditions.
• Battery: Weak batteries may not provide enough power to crank the engine and build up the necessary injection pump pressure.

It is important to use a diagnostic scanner to read trouble codes and identify the specific cause of the issue. Some issues may require professional assistance for accurate diagnosis and repair.

Poor transmission shifting operation

• Low fuel rail pressure: Check for common symptoms such as low power, a "Change fuel filter" message, increased smoke output, high exhaust gas temperatures, and a check engine light. Address the issue by following a checklist that includes changing the fuel filter, inspecting fuel lines for leaks or damage, replacing the fuel pressure relief valve, and checking the fuel pressure regulator for debris.
• Towing habits: If you are towing a heavy load, ensure that you are using the correct towing mode and maintaining the recommended rpm levels. Adjust your driving habits if necessary to prevent the transmission from searching for the right gear.
• Tuning issues or boost leak: Check for tuning issues or a boost leak that could be causing the transmission to hunt for gears. Monitor critical parameters such as boost pressure, exhaust gas temperature, coolant temperature, fuel rail pressure, and engine oil pressure to identify potential issues.
• Transmission problems: The Allison 1000 automatic transmission used in the 2006 Duramax has been known to have some issues. Consider upgrading the transmission if you are pushing over 400 horsepower or have a heavy right foot. Upgrades such as better friction material, key hydraulic modifications, a good transmission cooler, and a multi-disc torque converter can improve performance and durability.
• Faulty sensors or wiring: Check for any fault codes related to sensors or wiring that might be causing the transmission to malfunction. Ensure that all connections are clean, tight, and free of corrosion.
• Fuel filter: A dirty or clogged fuel filter can restrict fuel flow and affect transmission performance. Try changing the fuel filter and see if it improves shifting.
• Other mechanical issues: In rare cases, there could be more serious mechanical issues with the engine or transmission. If basic troubleshooting steps do not resolve the problem, consider taking your vehicle to a reputable diesel repair shop for a more thorough diagnosis and repair.

Increased smoke output

To diagnose the issue, it is recommended to check for fault codes, inspect the air filter, clean or replace the MAF sensor, and check the fuel system for leaks or restrictions. It may also be helpful to perform a smoke test to check for leaks in the intake system. If the problem is determined to be related to the fuel system, it may be necessary to replace the fuel filter, fuel pressure regulator, or injection pump. If the problem is with the turbocharger, it may be necessary to repair or replace the turbocharger or its associated components.

In some cases, the increased smoke output may be caused by modifications made to the vehicle, such as the installation of larger injectors or a higher-output injection pump. It is also possible that the smoke is being caused by a problem with the engine, such as a faulty piston or cylinder. In these cases, it may be necessary to perform more extensive diagnostics or repairs to resolve the issue.

High exhaust gas temperatures

• Towing Heavy Loads: Towing heavy trailers or climbing steep grades can increase exhaust gas temperatures. To mitigate this, ensure you're using the Tow/Haul mode while towing and maintain RPMs above 2000-2300 for flat roads and 2400-2800 for grades.
• Incorrect Tune: Using an aggressive or "hot" tune on your Duramax can lead to higher exhaust gas temperatures. If you're using an aftermarket tuner, try switching back to stock settings or using a more conservative tune. EFI Live tunes are often recommended for better control over engine parameters.
• Air Intake and Intercooler: The design of the air intake and intercooler can impact exhaust gas temperatures. Ensure your air intake is drawing cool air from outside the engine bay, as hot air from the engine compartment can increase temperatures. Consider upgrading to a cold air intake system and checking for leaks or damage in the intercooler boots.
• Turbocharger: A malfunctioning or damaged turbocharger can contribute to high exhaust gas temperatures. Inspect the turbocharger for any signs of damage, such as "flattened" fins. If the turbocharger is not functioning properly, it may need to be repaired or replaced.
• Exhaust System: Modifications to the exhaust system, such as installing a larger downpipe or a full exhaust system, can affect exhaust gas temperatures. Ensure that any modifications are compatible with your specific vehicle and engine configuration.
• Fuel System: While fuel pressure is not directly related to exhaust gas temperatures, ensuring a proper fuel supply is crucial for overall engine performance. The Duramax fuel system has a low-pressure side (under vacuum) and a high-pressure side (6000-26000 psi). Check for any leaks or restrictions in the fuel supply lines, as these can affect engine performance and, indirectly, exhaust gas temperatures.

It's important to monitor your exhaust gas temperatures closely, especially when towing or driving in challenging conditions. While the Duramax can handle brief periods of higher temperatures, sustained high temperatures can lead to potential engine damage. Always refer to the manufacturer's guidelines and seek the advice of a qualified diesel technician if you're unsure about any modifications or troubleshooting steps.

Frequently asked questions