Troubleshooting a Fuel Pressure Regulator

  • 1-2 hours
  • Beginner

Troubleshooting a fuel pressure regulator will expose a number of possible causes of potential failure of the pressure regulator. Injection systems regulate the amount of fuel required by the engine during a journey and supplies it with the correct amount needed.

Inside the Regulator

Inside the fuel pressure regulator there is a diaphragm on which a spring pushes to regulate the fuel supply. It is the spring’s tension which determines the level of fuel which passes through and these are usually set to their optimum level by the car manufacturer. Any fuel which is not used on that session is returned via the return line and taken back to the fuel tank for another cycle.


It is quite rare for a fuel pressure regulator to fail. The resulting symptoms will be a drop in fuel pressure. The firs thing to check is the vacuum hose which is attached to the pressure regulator. If the hose has become detached or has worn out, split or has punctures it will allow air inside and not function correctly. This result in pressure drop in the fuel regulator will affect the performance of the car and driving will be choppy and staggered.


You may also see black or darker smoke emitting from your exhaust pipe. This is a clear indication that something is wrong in the engine or the fuel system but also, black smoke could indicate other issues which are not connected to the fuel pressure regulator, so be sure what you are looking for.


If the diaphragm inside the regulator begins to leak, the fuel will seep into the vacuum hose. Pinch down on the fuel return line and check if the pressure rises again. If not there is trouble and you should look at the vacuum hose more closely.

Spark Plugs

Checking the spark plugs for signs of fouling will also provide evidence of a problem with the fuel pressure regulator. Have a look at each spark plug and make sure it is still in good condition. It should be clean and have the correct amount of gap. If the spark plug is dirty or rusty then replace it.

Stalling or Start Failure

If the spark plugs are all in good order and the car is failing to start in the mornings it does indicate that fuel is not reaching the system via the regulator. If there is an issue with the regulator and you are able to start the car, then you may find that if there is a problem the vehicle will also stall quite often. This is caused by fuel starvation where the regulator has not been guided to provide the level of fuel needed to either start the vehicle or keep it going. Again, test the return the line by pinching it and check the vacuum hose for signs of wear. Replace the vacuum hose if it is showing signs of breakage.