Checking Fuel Pressure: 871 Cummins Maintenance Guide

Checking the fuel pressure on a Cummins engine is an important part of maintenance and can help identify potential issues. The process involves using a fuel pressure gauge to measure the pressure at different engine speeds, such as idle and wide-open throttle (WOT). For a Cummins engine, the fuel pressure should be within a specific range, typically around 10-14 psi at idle and not dropping below 14 psi under load. There are different methods and tools for checking fuel pressure, including drilling and tapping the injection pump banjo bolt, using a Schrader valve on the fuel filter housing, or utilising a fuel injection test kit. It is also recommended to have an OBDII scanner to read error codes and assess the overall health of the engine.

Check the fuel pressure at the VP with a banjo bolt

Checking the fuel pressure at the VP with a banjo bolt is a common method for testing fuel pressure on a Cummins engine. Here is a step-by-step guide on how to perform this task:

Step 1: Prepare the Banjo Bolt

• Obtain a banjo bolt that fits your Cummins fuel system. You can purchase this part online or at an automotive store.
• Drill and tap the banjo bolt to create a 1/8" pipe thread. This will allow you to install a needle valve and tubing compression fitting.
• Install a male-to-female 1/8" needle valve with 1/8" tubing compression fitting into the drilled and tapped hole in the banjo bolt. This will help control fuel flow and protect your fuel pressure gauge.

Step 2: Prepare the Fuel Pressure Gauge

• Obtain a fuel pressure gauge that measures in low increments, preferably one that measures between 0-30 PSI. You can find these gauges at most auto parts stores or online.
• Connect the fuel pressure gauge to the needle valve using appropriate tubing. You may need to use an adapter or a fuel pressure tester kit for this step.

Step 3: Install the Banjo Bolt

• Locate the banjo bolt on the VP (fuel injection pump) of your Cummins engine. This is usually found on the fuel filter housing or the injection pump.
• Remove the stock banjo bolt and replace it with the drilled and tapped banjo bolt prepared in Step 1. Ensure that you use new washers or gaskets when installing the new banjo bolt to prevent leaks.

Step 4: Test the Fuel Pressure

• Start the engine and slowly open the needle valve until the fuel pressure gauge begins to read pressure. You may need to have an assistant in the cab of the vehicle to signal when pressure is being read.
• Observe the fuel pressure readings at idle and at different engine speeds (RPMs). For a Cummins engine, the fuel pressure should be between 10-22 PSI at idle and should not drop below 15 PSI under load.
• Pay attention to any fluctuations or surges in fuel pressure, as this may indicate an issue with the fuel system or the VP.

By following these steps, you can safely and effectively check the fuel pressure at the VP with a banjo bolt on your Cummins engine. This will help you diagnose any fuel-related issues and ensure that your engine is running optimally.

Use a mechanical fuel gauge to test the pressure

To check the fuel pressure on a Cummins engine, you can use a mechanical fuel gauge. This is a straightforward process, but it's important to take some safety precautions. Make sure you're working in a well-ventilated area, and don't smoke or have anything that could spark nearby. Wear safety glasses and gloves for protection.

Here's a step-by-step guide on how to use a mechanical fuel gauge to test the fuel pressure on your Cummins engine:

• Prepare the Engine: Start by ensuring the engine is completely cold. This is important for an accurate reading.
• Locate the Fuel Filter Housing: The fuel filter housing is usually located near the fuel tank. It has two brass baby bolts on top. You will be working with these bolts, so make sure you have the correct tools to unscrew them.
• Acquire the Correct Mechanical Fuel Gauge: Unscrew one of the brass baby bolts and take it with you to a local parts store. Tell them you need a mechanical fuel gauge that fits that specific port size. It's important to get the right size to ensure a tight seal and accurate readings.
• Check the Recommended Fuel Pressure: Before proceeding, check the recommended fuel pressure for your Cummins engine. The recommended pressure varies depending on the model and specifications. For example, for a 12-valve Cummins, the gauge must be at least 40 psi, with 60 psi being ideal. For a 2nd Gen Dodge 5.9L 24V Cummins, the recommended pressure is around 10 psi at idle and no more than a 3 psi drop at WOT (wide-open throttle).
• Attach the Mechanical Fuel Gauge: With the correct mechanical fuel gauge in hand, attach it to one of the brass baby bolts on the fuel filter housing. Make sure it's securely tightened to prevent leaks.
• Start the Engine: Once the gauge is attached, start the engine and let it idle. You can now proceed to take fuel pressure readings.
• Take Fuel Pressure Readings: Observe the gauge and note the fuel pressure reading at idle. Then, slowly rev the engine and check the pressure again. Compare these readings to the recommended fuel pressure for your specific Cummins engine. If the pressure is significantly lower than expected, you may have a fuel pump issue or a clogged fuel filter.
• Address Any Issues: If the pressure is low, you may need to address potential problems. This could include replacing the fuel filter or inspecting the fuel pump for any signs of wear or malfunction.

Remember to work safely and follow the recommended procedures for your Cummins engine model. Always refer to the manufacturer's guidelines and consult a professional if you're unsure about any steps.

Check the Schrader valve on the fuel filter housing

Checking the Schrader valve on the fuel filter housing is a straightforward process. The Schrader valve is located on the fuel filter housing, which is typically found on the driver's side of the engine.

To access the Schrader valve, look at the banjo bolt on the back of the housing where the line from the stock lift pump connects. The Schrader valve will be right there, but it may be hard to see as it faces the firewall. It will be covered by a black cap that resembles a valve stem cap. Remove this cap to access the Schrader valve.

Once you have located the Schrader valve, you can attach a fuel pressure gauge to it. For this purpose, a 30 psi gauge should be sufficient. You can borrow or purchase a gauge from an auto parts store.

After attaching the gauge, start the engine and slowly open the valve until the gauge begins to show a reading. This will allow you to measure the fuel pressure and determine if it is within the acceptable range.

It is important to note that the fuel pressure should not drop below 10 psi at any time. If you observe readings below this threshold, it may indicate an issue with the fuel system that requires further investigation or maintenance.

Monitor the lift pump pressure

To monitor the lift pump pressure on a Cummins 871, you can perform the following steps:

Firstly, locate the lift pump on your engine. It is usually found on the driver's side of the engine block, but on some vehicles, it may be underneath the car. You can start by opening the engine hood and looking for it.

Next, insert your ignition key and turn it on without starting the engine. Listen carefully for any swishing sounds coming from the lift pump. This sound indicates that the lift pump is functioning and will typically occur within 2 seconds of turning the ignition on. If you don't hear any sound, there may be an issue with the electrical connection.

To check the electrical connection, follow these steps:

• Locate the power supplier connection tube at the bottom of the lift pump.
• Disconnect the connection tube from the lift pump.
• Identify the positive and negative connections (the second pin is usually for grounding).
• Connect the tube to a multimeter or voltmeter.
• Start the ignition key (without cranking the engine) and check the meter reading.

If the meter reads 12V or more, the electrical connection to the lift pump is likely functioning correctly. If there is no reading, the issue may lie with the fuse box.

Another way to check the lift pump pressure is by using a fuel pressure gauge. Here are the steps:

• Open the engine hood and locate the lift pump.
• Connect the hose of the pressure gauge to the lift pump, being careful not to spill any fuel.
• Start the engine and observe the pressure reading on the gauge.

The correct pressure limit for most vehicles is between 30 and 50 PSI. If the pressure is below 30 or even 20 PSI, it indicates that the lift pump may be faulty. However, before replacing the lift pump, ensure that there is no water or air in the fuel rail, as this can also cause low fuel pressure.

Check for error codes

Checking for error codes is crucial when assessing the health of a Cummins engine. Fault codes indicate that your engine is experiencing a problem, and with Cummins engines, there are three different types of fault code statuses: inactive, active, and pending. Inactive codes occur outside of diagnostics, active codes pop up during diagnosis, and pending codes haven't been cleared and may require multiple warm-up cycles to be set to active.

To check for error codes, you'll need a diagnostic tool or scanner. A basic OBD2 scanner will do the trick, but for more detailed information, you may want to opt for a more advanced tool like the OBDLink. Once you have your scanner, follow these steps:

• Insert the key into the ignition.
• Cycle the key five times, switching it from "off" to "run" without cranking the engine.
• On the fifth cycle, leave the key in the "run" position (two clicks of the key).
• This will bring up any pending or active codes.

If you have any active codes, be sure to diagnose and address the issue before clearing the codes. Fault codes can provide valuable insights into potential problems with your Cummins engine, so it's important to address them promptly.

In addition to checking for fault codes, it's recommended to perform regular maintenance and stay on top of preventative repairs and replacements to keep your Cummins engine in its best shape.

Frequently asked questions