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. If the Ram has possible fuel-related problems, then running a fuel-pressure test can isolate them. 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.
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 out of the way. Screw the end of the fuel-pressure gauge onto the test port.
Start the Dodge Ram 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.
Turn the motor off and remove the pressure gauge from the test port. Use an old towel to wipe up any spilled fuel. Replace the test port cap.
