How do I know if the fuel pressure regulator is stuck open or leaking or if it is stuck closed? Engine with hard-start condition could be the result of a faulty fuel pressure regulator and not the fuel pump itself. Check for these signs while performing fuel pressure tests.
Make sure you have the appropriate equipment and tools before performing fuel pressure tests. Once you have ensured you hear the fuel pump running and have checked fuel system rest pressure and it is lower than the spec, look for the following possible signs of a faulty fuel pressure regulator:
- Once you have triggered the fuel pump, and you still have low or no fuel pressure, it could mean the fuel pressure regulator is leaking or stuck open.
- However, if the fuel pressure is high, it could mean the fuel pressure regulator is stuck closed.
- If you have low or no fuel pressure at rest, check if the fuel pressure regulator is allowing the fuel pressure to return to the tank.
The tension (pressure) of the spring inside the pressure regulator, which is pre-set by the manufacturer, could be defective and not pushing against the diaphragm to build allow sufficient fuel pressure to build inside it.
There can also be an issue that the diaphragm is leaking inside of the fuel pressure regulator. If this happens and the regulator is “leaking internally,” then fuel may enter the vacuum hose, which will cause various engine problems. Black smoke coming from the engine are signs of the engine running rich, possibly as a result of the diaphragm leaking inside of the fuel pressure regulator.
To check to see if the regulator is not allowing sufficient pressure to build in the system, close, or pinch block, the fuel return line. Now cycle the key a couple times. At this point, you should see maximum pump pressure on your fuel pressure gauge. (Call the tech line if you need this spec). If the pressure on the gauge doesn’t increase, it may be a faulty fuel pressure regulator. It is also important to check for leaking fuel injectors while checking the fuel pressure, as that could also be the cause of the vehicle engine not starting, hard-starting and sputtering.
Important to note: a bad fuel pressure regulator can also result in spark plugs fouling or misfiring, so it is also recommended to look at ignition issues as well.