A fuel pressure tester is a pressure gauge kit used to diagnose fuel system issues. If a car is hard to start, stumbles, or lacks power, it could be due to a failing fuel pump, a clogged fuel filter, or a bad fuel pressure regulator. The tester connects to a service port on the fuel rail (often a Schrader valve, which looks like a tire valve) and displays the fuel pressure in PSI while the engine is running or priming.
You compare the gauge readings to the vehicle's factory specifications. If the pressure is low, the engine will run lean, causing misfires and lack of power. If the pressure drops instantly when you turn the key off, it indicates a leaking fuel injector, a bad check valve in the fuel pump, or a leaking fuel line. The tester kit includes a relief valve and hose to bleed off the high pressure safely before you disconnect the tool, preventing fuel spray.