Increasing Fuel Rail Pressure: Easy Guide For Your Duramax

The Chevy/GMC Duramax is a popular diesel truck engine, but it has a common issue with low fuel rail pressure. This can cause a range of problems, from reduced engine power to increased smoke output and high exhaust gas temperatures. If you're experiencing these issues, there are a few things you can try to increase fuel rail pressure and get your truck running smoothly again.

First, check for common symptoms of low fuel rail pressure, such as reduced engine power and increased smoke output. If you're experiencing these issues, start by checking your fuel filter and changing it if necessary. Next, inspect the fuel lines for any leaks or damage. You may also want to consider installing a lift pump and keeping your fuel filters clean to avoid future issues.

If these basic repairs don't solve the problem, you may need to replace your injection pump or check for debris in the fuel pressure regulator. It's also worth monitoring your engine's PIDs in real time to see if you can catch the issue as it occurs.

Finally, if you're experiencing low fuel rail pressure while towing, it may be worth checking your fuel lines for kinks or collapses, as this can cause a fuel system restriction. You may also want to consider installing a lift pump to help maintain fuel pressure.

Change the fuel filter

To change the fuel filter on a Duramax, follow these steps:

Park your GM model truck in a well-ventilated area and turn the steering wheel clockwise until it stops. This will make it easier to access the fuel filter through the front wheel well. Turn off the engine and open the hood, propping it up with the locking rod.

Reach through the front passenger-side wheel well and remove the plastic guard from the rear of the wheel well. Use a flat-head screwdriver to pry off the small plastic clips holding the guard in place. Place the guard on the ground, and you will now be able to see and access the fuel filter.

Locate the water sensor at the bottom of the fuel filter. Follow the wires attached to the water sensor to the plug near the passenger-side valve cover and unplug it. Position the water sensor plug and wires so they hang below the fuel filter.

Place a drip pan under the truck, below the fuel filter. Slide a fuel filter strap wrench halfway up the fuel filter and turn it counter-clockwise to loosen the fuel filter. Finish unscrewing the fuel filter with your hands and place it on the passenger-side frame rail near the fuel filter housing.

Move to the top side of the engine and pull the fuel filter out of the engine compartment. Pour any excess diesel into the drip pan. Remove the water sensor with pliers.

Now, take your new Duramax fuel filter and screw the water sensor onto it. Tighten it with the pliers. Do not fill the new fuel filter with diesel; the fuel filter housing has an integrated hand pump that will be used to pump diesel from the fuel tank into the filter.

Lower the new fuel filter through the engine compartment down to the passenger-side frame rail. Move back to the front passenger-side wheel well and screw the fuel filter onto the fuel filter housing. Turn the fuel filter clockwise to tighten. Finish tightening the fuel filter with the strap wrench.

Move back to the top side of the engine and open the relief valve on the top side of the fuel filter housing by turning it counter-clockwise. This will allow diesel to bleed out of the relief valve hole. Prime the new fuel filter by pushing in on the black primer cap on top of the fuel filter until diesel starts to run out of the relief valve. Close the relief valve.

Turn the ignition to the accessory position for about 15 seconds, then crank the engine. Inspect the new fuel filter for any diesel leaks. Turn the engine off. Reinstall the plastic guard back onto the rear of the front passenger-side wheel well.

Finally, pull the drip pan out from under the truck and shut the hood.

Check for leaks in fuel lines

To check for leaks in your fuel lines, start by inspecting the fuel lines from the fuel filter to the injection pump and from the CP3 to the fuel rails for any leaks or damage. If you find any leaks, you can try to repair them by replacing the damaged section of the fuel line with a piece of compatible rubber fuel hose and securing it with worm gear clamps. However, it is recommended to replace the entire fuel line set as soon as possible, as fuel leaks can be dangerous and cause a mess.

If you are having trouble locating the fuel leak, you can try pressurizing the fuel system to create a more noticeable leak. This can be done by adding an air line to the fuel fill nozzle and pressurizing the fuel tank to about 4-5 lbs. You can also try using an oil squirt can to apply a few drops of motor oil around the threads and hose-to-barb areas of the fuel lines. If there is a leak, you should see the oil being sucked into the leak or dripping out.

Another method to check for leaks is to use clear tubing and look for bubbles, or perform a leak-down test using a Kent Moore Gauge connected to the Schrader valve test port. For the leak-down test, pump the primer until hard, and if the pressure drops too quickly (as measured on the gauge), it indicates a leak. If the pressure drops from 10 PSI to 2 PSI in less than one minute, remove the fuel outlet line from the filter and cap it. Then, remove the ignition 1 relay and crank the engine for 2-15 second intervals; the high-pressure pump should pull at least 12 inches of vacuum.

It is important to address any fuel leaks as soon as possible to prevent further issues and potential safety hazards.

Change the fuel pressure relieve valve

To change the fuel pressure relieve valve, follow the steps below:

Step 1: Disconnect the negative battery terminal

Before starting any work on your Duramax, it is important to disconnect the negative battery terminal to prevent any accidental short circuits. This will also reset the computer, which can help clear any error codes related to low fuel rail pressure.

Step 2: Relieve the fuel system pressure

This is an important safety step to prevent fuel leakage and reduce the risk of injury. Make sure to relieve the pressure in the fuel system before proceeding with any repairs or maintenance. You can do this by removing the fuel pump fuse or relay and then running the engine until it stalls. Turn the ignition off and wait for at least 3 minutes to ensure that all pressure is released.

Step 3: Locate the fuel pressure relief valve

The fuel pressure relief valve is usually located on the fuel rail, which is the metal tube that carries fuel to the injectors. It is often held in place with a clamp or bracket. In some cases, you may need to remove other components, such as the intake manifold, to access the fuel rail and the relief valve.

Step 4: Remove the old fuel pressure relief valve

Before removing the old valve, place a clean rag or container under the valve to catch any spilled fuel. Then, using the appropriate size wrench or socket, carefully loosen and remove the valve from the fuel rail. Be sure to inspect the valve for any signs of damage or wear, such as a worn-out spring.

Step 5: Install the new fuel pressure relief valve

Before installing the new valve, clean the area around the fuel rail and the valve seat to ensure that there is no dirt or debris that could cause a leak. Lubricate any new O-rings on the valve with clean engine oil and carefully thread the new valve into the fuel rail by hand. Once it is hand-tight, use a torque wrench to tighten the valve according to the manufacturer's specifications. Do not overtighten, as this can damage the valve or the fuel rail.

Step 6: Reassemble and reconnect the battery

Reinstall any components that were removed to access the fuel rail and relief valve. Be sure to tighten all clamps and connections securely. Finally, reconnect the negative battery terminal and start the engine to check for any leaks. If there are no leaks and the engine runs smoothly, your fuel pressure relief valve replacement is complete.

Check the fuel pressure regulator for debris

To check the fuel pressure regulator for debris, start by locating the regulator on the CP3 or CP4. Look for metal shavings on the regulator screen, as this is a clear indication of failure. If you notice any debris, you will need to have all fuel system parts cleaned, the pump replaced, and the injectors tested or potentially replaced.

Checking the fuel pressure regulator for debris is an important step in diagnosing low fuel rail pressure issues in Duramax trucks. This issue can manifest in various ways, such as low power, a "change fuel filter" message, poor transmission shifting, increased smoke output, high exhaust gas temperatures, and a check engine light with code P0087. When addressing the issue, it is recommended to start with cheaper and easier repairs first and work your way up.

In addition to checking the fuel pressure regulator for debris, there are several other items on the checklist to address low fuel rail pressure. These include changing the fuel filter if it has not been changed recently (within the past 5,000 miles), inspecting fuel lines for leaks or damage, changing the fuel pressure relief valve to a Race Fuel Valve, and checking or changing the CP3 or CP4 injection pump.

Most fuel rail pressure issues can be avoided with routine maintenance, additional filtration (such as a lift pump), and addressing minor issues promptly. It is important to keep fuel filters clean and fresh, invest in a lift pump, and purchase fuel from reputable sources to minimise the risk of being stranded due to low rail pressure issues.

Check or change the injection pump

To check or change the injection pump, you must first identify whether the pump is faulty. This can be done by checking for fuel leaks, as well as checking for specific diagnostic codes, such as P0087, which indicates low fuel rail pressure. If you suspect that the injection pump is faulty, you can attempt to replace it yourself, but this is a complex and time-consuming process that may be better left to a professional.

Identifying a Faulty Injection Pump

Before attempting to replace the injection pump, it is important to confirm that it is faulty. There are several signs that can indicate a problem with the injection pump. One common symptom is a "Change fuel filter" message displayed in the driver information center (DIC). Another indication of a faulty injection pump is low engine power, which may manifest as reduced speed or an "Engine power reduced" message in the DIC. Other possible symptoms include poor transmission shifting operation, increased smoke output, and high exhaust gas temperatures (EGTs).

One of the most telling signs of a faulty injection pump is the presence of metal shavings in the fuel system. This can be checked by inspecting the Fuel Control Actuator (FCA), also known as the fuel pressure regulator or MPROP. To access the FCA, you will need to remove several components, including the AC compressor. Once you have access to the FCA, you can unbolt it and carefully inspect the end for any metal shavings or debris, which would indicate the failure of the CP4 injection pump.

Replacing the Injection Pump

If you have confirmed that the injection pump needs to be replaced, you have the option of doing it yourself or taking your vehicle to a mechanic or dealership. Replacing the injection pump is a complex and time-consuming task, so unless you have some mechanical expertise and are comfortable with the process, it may be best to leave it to a professional.

If you decide to replace the injection pump yourself, be prepared for a lengthy and challenging process. The injection pump is located deep in the valley of the engine, so you will need to remove a number of components to access it, including the air intake system, turbo inlet, air filter, upper intake elbow, EGR coolers, intake Y bridge, serpentine belt, cooling fan and shroud, AC compressor, and alternator. Once you have access to the injection pump, you will need to disconnect the low-pressure supply and return lines, the feed for the 9th injector, the high-pressure steel lines feeding the fuel rails, and the electrical connections. The injection pump is held in place by four bolts, which can be accessed from the front side of the engine above the timing cover.

When removing the injection pump, be careful not to drop any hardware into the opening, as this could cause damage to the cam gear. It is also important to note that you will need to time the new injection pump if you are installing a CP4 pump. This involves lining up the dots on the CP4 gear and the cam gear during installation. If you are installing a CP3 retrofit kit, timing is not necessary.

In addition to replacing the injection pump, you will also need to clean or replace any fuel system components that may have been contaminated by metal shavings, including the fuel tank, fuel lines, fuel filter, fuel rails, and injectors. This is important to prevent collateral damage when you start the engine for the first time after the repair.

Preventing Injection Pump Failure

To prevent injection pump failure, it is important to change your fuel filter regularly and use a fuel additive that improves lubricity. You can also install an aftermarket lift pump to alleviate stress on the injection pump and extend its life.

Frequently asked questions