Checking Fuel Pressure: 12V Cummins Maintenance Guide

The Cummins 5.9-liter, 12-valve engine is a large diesel engine that eventually became the stock engine for the Dodge Ram pickup during the 1990s and 2000s. These engines come equipped with an easy-access test port, referred to by some as a Schrader valve. The fuel-pressure gauge can be screwed directly onto this port for testing. To check the fuel pressure, pop the hood on the Dodge Ram and locate the test port on the left-hand front side of the engine compartment. Unscrew the valve cap and pull it back, then screw the end of the fuel-pressure gauge onto the test port. Start the engine and allow it to run for around five minutes. Examine the fuel-pressure reading. If it still appears to be fluctuating, give it a few more minutes until the level peaks out. The pressure should read between 15 to 18 psi.

Drilling and tapping the injection pump banjo bolt

First, ensure you have the correct tools and materials. You will need a drill, a 1/8" NPT taper tap, a 1/8" needle valve, 1/8" tubing compression fitting, 1/4" tubing for protection, and anti-seize lubricant or Permatex #2. It is also recommended to have a boost, air, water, or fuel pressure gauge that can measure at least 40-60 psi.

Next, locate the injection pump banjo bolt. This bolt is typically found on the top of the injection pump. Before drilling, clean the area thoroughly as you will be working on the clean side of the filter.

Now, you can begin drilling. Drill a hole straight through the centre of the banjo bolt, being careful to maintain a steady hand and a straight drill bit. It is recommended to drill from the inside of the bolt outwards to ensure accuracy.

Once the hole is drilled, you can start tapping. Using your 1/8" NPT taper tap, carefully create threads on the inside of the hole. This process involves cutting a spiral path into the drilled hole to allow for the secure insertion of the needle valve. Take your time with this step to avoid damaging the threads.

After tapping, it's time to assemble the components. Install the male x female 1/8" needle valve into the tapped hole, ensuring it is secure and tight. Then, attach the 1/8" tubing compression fitting to the needle valve. You may also want to add a boost gauge or oil pressure tubing through a 1/4" protective sleeve to prevent cuts and kinks. Remember to use anti-seize lubricant or Permatex #2, not Teflon tape, as it doesn't work well with diesel.

Finally, you can test your setup. Start the engine with the needle valve closed, then slowly open it until you can read the fuel pressure on the gauge. Adjust the packing nut under the valve handle to secure the setting. The needle valve will help control pulsation and buzzing and can be shut down in case of a leak.

By following these steps, you will have successfully drilled and tapped the injection pump banjo bolt, allowing you to monitor the fuel pressure on your 12v Cummins engine.

Using a fuel-pressure gauge

To check the fuel pressure on a 12V Cummins engine, you can use a fuel-pressure gauge. Here's a step-by-step guide on how to do it:

Step 1: Prepare the Fuel-Pressure Gauge

• Ensure you have a suitable fuel-pressure gauge that reads at least 40 PSI, with 60 PSI being ideal. The gauge can be labelled for boost, air, water, fuel, or it can be unlabelled.
• Obtain a 1/8" needle valve, a plastic oil pressure tubing kit with compression fittings, and 1/4" tubing for a protective sleeve.

Step 2: Locate the Test Port

Open the hood of your Dodge Ram and locate the test port on the left-hand front side of the engine compartment. This test port is also known as a Schrader valve.

Step 3: Connect the Fuel-Pressure Gauge

• Unscrew the valve cap at the test port and set it aside.
• Screw the end of the fuel-pressure gauge onto the test port securely.

Step 4: Start the Engine and Check Fuel Pressure

• Start the engine and let it run for around five minutes.
• Observe the fuel-pressure reading on the gauge. If the reading fluctuates, allow a few more minutes for it to stabilise and peak out.
• The fuel pressure should ideally be between 15 to 18 PSI. However, some sources suggest that the pressure should be between 17-22 PSI at idle, 25-35 PSI at 2500 RPM with no load, and should never drop below 15 PSI under load for extended periods.

Step 5: Remove the Fuel-Pressure Gauge

• Turn off the engine.
• Carefully remove the fuel-pressure gauge from the test port.
• Use an old towel or rag to wipe up any spilled fuel.
• Replace the test port cap.

Additional Tips:

• When connecting the fuel-pressure gauge, do not use Teflon tape as it is not compatible with diesel. Instead, use anti-seize lubricant or Permatex #2.
• Ensure that all components are clean and spotless, especially when working on the clean side of the filter.
• Be careful not to overtighten compression fittings, as this can lead to leaks. Finger-tighten them and then use a wrench for only one half turn.
• If you need to adapt the gauge to the bleed screw on the fuel filter, you can use an appropriate adapter, but note that these are intended for temporary use only.

Locating the test port

To locate the test port, begin by popping the hood of the Dodge Ram. The test port will be on the left-hand side, towards the front of the engine. It is important to note that this test port is specifically for the fuel-pressure gauge and will have a valve cap that needs to be unscrewed before you can begin your fuel-pressure test.

Once you have located the test port, simply unscrew the valve cap and set it aside. You can then screw the end of your fuel-pressure gauge directly onto the test port. Ensure that the gauge is securely attached to the test port to prevent any fuel leaks during the testing process.

It is worth noting that there are alternative methods to checking fuel pressure on a 12V Cummins engine. Some individuals choose to tap into the rubber hose that connects the fuel filter canister to the VP, or drill and tap into the injection pump banjo bolt. However, the method described above, utilising the test port, is the easiest and most direct approach.

By following these steps, you will be able to locate the test port on your 12V Cummins engine and proceed with your fuel-pressure test. Remember to exercise caution when working with any fuel system and ensure proper ventilation in your work area.

Reading the fuel-pressure

Reading the fuel pressure on a 12-valve 5.9-liter Cummins engine involves the following steps:

First, locate the test port on the left-hand front side of the engine compartment. This is also referred to as the Schrader valve. This engine model comes equipped with an easy-access test port. Unscrew the valve cap and set it aside.

Next, screw the end of the fuel pressure gauge onto the test port. Start the engine and let it run for around five minutes. Observe the fuel pressure reading. If the reading is still fluctuating, allow a few more minutes for the level to stabilize. For a 12-valve engine, the reading should be at least 40 psi, with 60 psi being ideal.

If you are experiencing issues with the engine, a fuel pressure test can help isolate the problem. A healthy 12-valve Cummins engine should have a fuel pressure reading between 15 to 18 psi. If your reading is below this range, there may be an issue with the fuel system or a leak in the engine.

Additionally, you can monitor the fuel pressure at different engine speeds. At idle, the pressure should be between 17-22 psi, and at 2,500 rpm with no load, it should be a minimum of 25 psi. If the supply pressure is below these values, you can try restricting the fuel return hose by pinching it with pliers. If the pressure returns to normal, replace the overflow valve. If not, the lift pump may need replacement.

It is important to ensure that your engine is well-maintained and that all fuel-related components are in good working condition to avoid potential issues and ensure optimal performance.

Maintaining fuel-pressure

Maintaining Fuel Pressure on a 12V Cummins

The Cummins 5.9-liter, 12-valve engine is a large diesel engine that was eventually used as the stock engine for the Dodge Ram pickup during the 1990s and 2000s. Maintaining the fuel pressure in your Cummins engine is crucial to its performance and longevity. Here are some detailed instructions and tips to help you keep your fuel pressure in check:

Checking Fuel Pressure:

First, you need to locate the test port, also known as the Schrader valve, on the left-hand front side of the engine compartment. Unscrew the valve cap and set it aside. Screw the fuel pressure gauge directly onto the test port. Start the engine and let it run for about five minutes. Observe the fuel pressure reading. If it's still fluctuating, give it a few more minutes until the level stabilizes. For a 12V Cummins, the pressure should ideally be between 15 to 18 psi at idle. Turn off the engine, remove the pressure gauge, and wipe up any spilled fuel with an old towel. Finally, replace the test port cap.

Modifying the Injection Pump Banjo Bolt:

Some Cummins owners choose to modify their injection pump banjo bolt to accommodate a fuel pressure gauge. This method involves drilling and tapping the top of the banjo bolt to 1/8" pipe thread. Install a male x female 1/8" needle valve with a 1/8" tubing compression fitting. You can use boost gauge or oil pressure tubing through some 1/4" tubing to protect against cuts and kinks to the gauge. Ensure the gauge reads at least 40 psi, with 60 psi being ideal. When working on this modification, keep everything spotless as you are dealing with the clean side of the filter. Be careful not to overtighten the compression fittings, as this can cause leaks.

Identifying and Resolving Low Fuel Pressure:

If you suspect low fuel pressure, there are a few troubleshooting steps you can take. First, check the fuel pressure at idle and at 2500 rpm with no load. If the pressure is below 17 psi at idle or below 25 psi at 2500 rpm, try restricting the fuel return hose by pinching it with pliers. If the pressure returns to normal or higher, you may need to replace the overflow valve. If the pressure doesn't climb, it could indicate an issue with the lift pump.

Maintaining the Lift Pump:

The lift pump plays a crucial role in maintaining adequate fuel pressure. If you notice rough engine performance at lower rpm or suspect a weak lift pump, it may be time for a replacement. When replacing the lift pump, consider using a stud and nut instead of a bolt to secure it. This makes it much easier to compress the spring and start the bolt. Be careful when removing the old pump, as the actuator arm may fall off and drop into the engine, turning a simple job into a major one.

By regularly checking your fuel pressure and maintaining the fuel system, you can help ensure the optimal performance and longevity of your 12V Cummins engine.

Frequently asked questions