Repairing Yukon's High-Pressure Fuel Line: A Step-By-Step Guide

If your GMC Yukon is experiencing issues with its high-pressure fuel line, it may be necessary to repair or replace the fuel pump. The fuel pump is responsible for delivering fuel from the tank to the fuel injectors, and a failing pump can cause various issues, including engine stalling, loss of power, and the check engine light coming on. Before attempting any repairs, it is important to disconnect the battery to reduce the risk of fire. In some cases, you may need to drain the fuel and remove the fuel tank to access the pump. It is recommended to replace the fuel filter at the same time as the pump and to verify that the issue is indeed a faulty pump and not a problem with the power supply.

Diagnosing fuel pump issues

• Whining Noise: A damaged fuel pump may make a loud, whining noise, indicating a problem. This is usually accompanied by a high-pitched whine after the pump has primed.
• Stalling: Stalling is often a sign of low fuel pressure, which can be caused by a failing fuel pump. The engine may restart after several minutes, but this is due to the fuel pump struggling to maintain consistent fuel pressure.
• Trouble Starting: If your Yukon is having difficulty starting or not starting at all, it could be due to a faulty fuel pump. This is usually characterised by long cranking times.
• Power Loss: A sudden loss of power when accelerating can indicate a failing fuel pump. This is because the pump cannot deliver the required amount of fuel to the engine when you step on the gas pedal.
• Engine Sputtering: If your engine sputters or cuts out briefly at high speeds, it may be due to the fuel pump being unable to provide a consistent flow of fuel.
• Check Engine Light: Keep an eye out for the check engine light. If it's on and displaying a code related to low fuel pressure, such as P0087, it's a good indication that your fuel pump may be failing.
• Recalls: It's worth checking if your specific Yukon model has been subject to any recalls related to the fuel pump. There have been reports of issues with the fuel pump control module and fuel injector recalls.

If you suspect a fuel pump issue, it's essential to get it checked by a professional mechanic. They can perform diagnostic tests, such as using an OBD II scanner to check for relevant codes, checking fuel pressure, inspecting the fuel filter and lines, and verifying the electrical and mechanical condition of the fuel pump.

Disconnecting the battery

Locate the battery: The battery in a GMC Yukon is typically located in the engine compartment, usually in one of the front corners. It is a large, rectangular black box with two terminals, marked positive (+) and negative (-).

Gather the necessary tools: You will need a basic set of tools, including a wrench or socket set to loosen and remove the battery cables. It is recommended to have a pair of safety gloves and goggles to protect your hands and eyes during the process.

Loosen the negative cable: Before disconnecting the battery, make sure that all accessories in the vehicle are turned off, including the headlights, air conditioning, radio, etc. Start by identifying the negative cable, which is usually black and connected to the negative (-) terminal. Use the appropriate size wrench or socket to loosen the nut that secures the cable to the terminal. Do not allow the wrench to touch any metal parts of the vehicle to avoid creating a spark.

Remove the negative cable: Once the nut is loosened, carefully lift the cable off the terminal. You may need to wiggle it gently to detach it completely. Be cautious not to let the cable touch any metal parts of the vehicle. If the cable is stuck, you can use a battery terminal puller tool to safely remove it. Place the cable to the side, ensuring it does not touch any metal surfaces.

Loosen and remove the positive cable: Identify the positive cable, which is usually red and connected to the positive (+) terminal. Use the wrench or socket to loosen the nut securing the cable. Again, be careful not to let the wrench touch any metal parts. Remove the cable from the terminal and place it away from metal surfaces.

Secure the battery cables: To prevent accidental contact, it is important to secure the battery cables. You can use a cable tie or tape to hold them in place, ensuring they do not touch any metal parts of the vehicle.

Check for any leaks or damage: Before proceeding with the fuel line repair, inspect the battery and surrounding area for any signs of leaks, corrosion, or damage. If there is any leakage or corrosion on the battery terminals, clean them with a solution of baking soda and water. Ensure that the area is dry before proceeding.

Reinstallation: When the repair is complete, you will need to reconnect the battery. Start by reconnecting the positive cable to the positive terminal and securing it with the appropriate nut. Then, reconnect the negative cable to the negative terminal and secure it. Ensure that the cables are tightly connected and the nuts are properly tightened. Finally, ensure that all tools and safety equipment are removed from the engine compartment.

Remember, working with the fuel system can be dangerous, and it is crucial to take all necessary precautions. If you are unsure or uncomfortable with any part of the process, it is always best to consult a qualified mechanic or seek professional assistance.

Removing the fuel pump

To remove the fuel pump from a GMC Yukon, you will first need to disconnect the battery to reduce the chance of a fire.

If the fuel pump is inside the fuel tank, you will need to remove the access cover. In some cases, you may need to drain the fuel before removing the access panel. With the cover off, you can then replace the pump and pre-pump filter screen.

If the pump is outside the tank, simply disconnect the fuel lines, remove the pump, and install the new one.

Once the pump is replaced, another check will be done to ensure there are no fuel leaks and that the problem is solved. It is recommended that the fuel filters are replaced at the same time as the fuel pump.

> "I dropped the fuel tank by myself [...] Fuel line connections were kinda a pain. I remember driving on E for a long time and still having two or three gallons left in the tank. I replaced the working fuel pump for good measure because the one in the truck at the time was close to ten years old and the fuel gauge quit working some time ago. I was surprised how clean the inside of the tank was after 16 years and 260K miles. Get a good acdelco or delphi pump and change out the connector too. New pump is so quiet I can barely hear it now!"

> "I've measured everything & figured out where the pump is & raised the driver's side enough to get under it. I'm going to drill several 1/4" holes in the floor right behind the rear seat & use my sabre saw to cut from hole to hole. I'm going to cut the blades shorter, just to make sure they don't catch any wires or hoses. There's a crossmember for the floor that might get in the way, but I do not think it will & if it does, I'll trim part of it off. I'm going to replace the fuel filter first & I've already tested the fuel pump relay & it is OK!"

Replacing the fuel pump

The fuel pump is a crucial component of your GMC Yukon's fuel system, delivering fuel from the tank to the fuel injectors. It is powered by an electric motor and located inside or outside the fuel tank. When it fails, your engine will not receive enough fuel to run smoothly, and you may experience a loss of engine power or an inability to start the car.

When to Replace the Fuel Pump

Look out for the following signs that your fuel pump needs replacing:

• Leaks
• Unusual noises
• Lack of engine power
• Inability to start the car
• Check engine light is on

How to Replace the Fuel Pump

• Disconnect the battery to reduce the risk of fire.
• If the pump is inside the fuel tank, remove the access cover. If there is no access cover, drain the fuel, and then remove the fuel tank from the vehicle.
• Disconnect the fuel pump supply and return hoses, EVAP system hoses, and electrical connections.
• Remove the faulty fuel pump.
• Attach any reusable brackets and pick-up screens to the new pump.
• Install the new fuel pump.
• Reconnect all hoses and electrical connections.
• Refill the fuel tank and run the engine to test for leaks.

Important Considerations:

• Fuel system repairs are dangerous, so it is recommended to leave this job to a professional mechanic.
• Always replace the fuel filters when replacing the fuel pump.
• If the fuel pump relay is known to fail, replace it when installing the new pump.
• Keep the fuel tank at least a quarter full to maximise the life of the new fuel pump.

Testing for leaks

Step 1: Check for External Leaks

Start by inspecting the fuel system for any visible signs of fuel leaks. This includes examining the fuel pump, fuel lines, injectors, and fittings for any traces of fuel or damp spots. If you notice any wet spots, it indicates a leak that needs to be addressed.

Step 2: Pressure Test

If there are no obvious external leaks, the next step is to perform a pressure test on the fuel system. This will help identify any leaks that may not be readily apparent. To do this, you'll need to install a fuel pressure gauge and increase the pressure in the system. Follow these steps:

• Install a fuel pressure gauge: You can purchase one from an auto parts store. Connect it to the fuel system according to the manufacturer's instructions.
• Increase the pressure: Use the hand primer pump or an external source to increase the pressure in the fuel system.
• Check for pressure drop: Once the desired pressure is reached (typically around 10 PSI), observe the gauge for any pressure drop over a set period (e.g., 1 minute). A significant pressure drop indicates a leak.
• Inspect specific components: If there is a pressure drop, start inspecting individual components, such as the fuel filter housing, injector lines, and fuel pump fittings, for leaks.

Step 3: Use a Leak Dye or Soapy Water

In some cases, a more direct approach may be necessary to pinpoint the exact source of the leak. Here are two methods to try:

• Leak Dye Test: Add a fluorescent dye to the fuel and run the engine. Then, use a black light to inspect the fuel system for signs of dye leakage. This method is effective in identifying even small leaks.
• Soapy Water: Apply soapy water to the suspected leak areas. If there is a leak, the escaping fuel will cause the soapy water to bubble, making it easier to locate the exact source.

Step 4: Check the Fuel Tank and Ventilation

If you still haven't identified the leak, the fuel tank and ventilation system should be inspected:

• Fuel Tank: Ensure the fuel tank vent hoses are properly connected and not damaged. A blockage or disconnection in the ventilation system can cause pressure issues and affect the fuel system's performance.
• Fuel Cap: Check the fuel cap to ensure it seals properly. A faulty fuel cap can cause fuel to evaporate, leading to a loss of pressure.

Remember, working with the fuel system can be dangerous due to the risk of fire. Always exercise caution, and if you're uncomfortable with any part of the process, it's best to consult a professional mechanic.

Frequently asked questions