How to Replace the Fuel

Relieving Your Fuel System
1. Park your ML320 in a safe location on level ground. Turn off the ignition and engage the parking brake. Open the trunk. Locate the service area against the driver’s side wall of the trunk. Open the service area using a flathead screwdriver.
2. Locate the rear fuse box inside the service area. Open the fuse box using a screwdriver. Remove the fuel relay by pulling it gently pulling it with your fingers. Set the fuel relay aside in a safe place.
3. Locate the fuel filler cap on the passenger’s side of the vehicle. Unscrew the fuel cap. Open the hood. Disconnect the negative cable from the battery in the hood area.
Return Fuel-Injection System
4. Relieve your fuel system. Locate the fuel rail along the passenger’s side of the rear firewall. Inspect the area where the fuel rail connects to the return fuel line. The fuel pressure regulator is located just near the end of the fuel rail.
5. Disconnect the return fuel line from the fuel pressure regulator using an adjustable wrench. Remove the vacuum hose from the pressure regulator as well.
6. Remove the snap ring from the pressure regulator using snap-ring pliers. Set the snap ring aside in a safe place. Remove the pressure regulator by pulling it gently using your fingers. Discard the old regulator.
7. Replace the old regulator with a new one. Apply engine oil to the O-rings of the new regulator to lubricate it. Align the regulator with the fuel rail and press it into the fuel rail firmly. Secure the pressure regulator using the snap ring and snap-ring pliers.
8. Connect the return fuel line and the vacuum hose to the fuel pressure regulator. Attach the negative cable to the battery. Replace the gas cap to the fuel tank. Go to the service area in the trunk and replace the fuel relay.
Returnless Fuel-Injection System
9. Relieve your fuel system.
10. Crawl underneath your vehicle from the driver’s side. Locate the fuel filter along the fuel line just below the driver’s seating area. Identify the fuel filter as a metallic-colored cylinder approximately three inches in diameter. The fuel pressure regulator is inside the fuel filter.
11. Remove the fuel line from the fuel filter using an adjustable wrench. Search the fuel filter for a bolt that secures it to the fuel filter mounting bracket. Remove this bolt and set it aside in a safe place. Discard the old fuel filter.
12. Replace the old filter with a new one. Install the fuel filter so that the arrow on the side of the filter faces towards the front of the vehicle. Secure the filter to the mounting bracket with a bolt. Attach the fuel line to the fuel filter and tighten it using a wrench.
13. Crawl from underneath the vehicle. Attach the negative cable to the battery. Replace the gas cap to the fuel tank. Go to the service area in the trunk and replace the fuel relay.