Testing the fuel pressure regulator is a good of knowing whether a vehicle is receiving the appropriate level of fuel or not. The test starts with raising the car hood and locating the test port on the fuel injection rail. Once found, the test port cap needs to be removed by twisting counter-clockwise. Then the fuel pressure gauge is screwed into the same port after the cap is place safely out of the way (don’t lose it or the car won’t run right).
The engine is then started up and left to run in idle. The pressure gauge should have a reading between 45 and 55 psi for normal pressure. That said, a throttle body injection system could read much lower, in the range of 15 to 18 psi instead. To be exactly sure, the given car model’s owner manual should have the correct reading specified for double-checking. The car will need work if the results are outside the normal range.
Based on the results, turn the engine off and remove the gauge. Re-insert the test port cap and tighten it clockwise. If the results are out of normal range, the regulator may be off or the test gauge may be bad. Produce the results for a mechanic to followup with a more thorough pressure test. If he gets the same results, the next step may require a vapor leak test in the fuel line system to see where the pressure is being lost.