Signs That Your Fuel Regulator Is Bad

Updated April 17, 2017

Virtually every car on the road today has a fuel-pressure regulator. As part of the fuel-injection system, your car's regulator is designed to maintain constant fuel pressure so the engine has enough gasoline to operate properly. A faulty fuel-pressure regulator can have many of the same symptoms as a failed fuel pump, among other mechanical problems. Knowing how to confirm fuel-pressure regulator trouble can help you avoid unnecessary or costly car repairs.


The fuel-pressure regulator works via a programmed spring that pushes against a diaphragm, which in turn closes or opens a valve into the engine to govern fuel pressure. A problem with the spring or diaphragm could force the regulator to fail. Some fuel-pressure regulators give out when cracks develop in the seals that block fuel from leaking. Each regulator has sensors that keep fluid and pressure balances inside the regulator; those sensors can stop working properly, and that could hurt the device's effectiveness. Splits in the vacuum hose serving the regulator can also create performance problems.


A bad fuel-pressure regulator could cause black smoke to pour out of your car's exhaust pipe. You might also see a coating of fuel, oil or carbon on the insulator nose at the firing tip of your spark plugs. Your car might stumble or shudder as you accelerate, which indicates a lack of fuel pressure, and it could idle roughly. A faulty fuel-pressure regulator will often make it tough to start your car, or make your car burn noticeably more gasoline than normal.


Several tests can determine whether your fuel-pressure regulator has failed. Car-parts stores will scan your engine with a diagnostic code reader. The results will tell you if you have regulator-related problems. Any codes that reflect piston misfiring or higher-than-normal carbon emissions can indicate regulator trouble. Or test the regulator yourself with a fuel-pressure gauge. Attach the gauge to the gauge port on the regulator, which is a small metal cylinder underneath the car on the fuel rail. Depending on your manufacturer's engine specifications, you should see a pressure of 13.6kg. per square inch to 36.3kg. per square inch while your engine idles.


Installing a new fuel-pressure regulator isn't a job for inexperienced or amateur mechanics, because it requires precision work around fuel lines and vacuum hoses. A professional mechanic or car dealer can replace your fuel-pressure regulator. If you're looking to save money, you can comparison-shop for a new regulator at any auto-supply store and take your purchased regulator to a mechanic or car dealer for installation.

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