The Chevy Cobalt was introduced in 2005 as Chevrolet's compact or subcompact car. The model's fuel delivery is electronic throttle-controlled sequential multi-port fuel injection. High flow injectors are an available option, used primarily with engine upgrades compatible with the use of nitrous. Signs of impaired fuel delivery include low power, hard starting and engine stalling while driving.
Open the hood of the Chevy Cobalt when the engine is cool.
Locate the fuel pressure test port on the Cobalt engine fuel line. If you need help finding it, refer to the owner's manual for a diagram of the engine.
Remove the cap from the test port and attach a standard fuel pressure gauge. Screw the connector on tightly so you get a true reading.
Hold the gauge so you can see the dial. Ask a helper to turn the ignition key to the first position. Do not start the car. Watch the gauge needle settle. Record this as the first pressure reading.
Remove the vacuum line from the fuel pump pressure regulator and check for fuel. Refer to the owner's manual for the line's location. No fuel should be present in the line. If there is, the engine problems are likely caused by a faulty fuel pump pressure regulator, which means the fuel is not adequately pressurized when being sent to the injectors, so there isn't enough fuel in the engine for it to run properly. If there is no fuel, reattach the vacuum line and continue with the fuel delivery diagnostic.
Start the engine and let it idle while you remove the vacuum line again. Watch the pressure gauge. It needs to register between five and ten pounds psi. If the needle does not move, the pressure regulator is malfunctioning and needs to be replaced.
Leave the engine on and watch the pressure gauge as a helper works the throttle. The gauge needs to register approximately five psi. If it moves down, the fuel pump is malfunctioning and needs to be replaced. Another option is that the fuel filter is clogged and needs to be replaced.
Start the engine and remove the fuel pump relay while the engine is running to relieve fuel pressure inside the engine. Any pressurized fuel in the lines is used and the engine quickly dies, allowing removal of the fuel filter without danger. Turn the engine off.
Inspect the fuel filter for clogs. Use two wrenches the size of the fuel filter fittings. There are two fittings that differ in size. Grip the fittings with the wrenches and then drape a rag or shop cloth over the fittings and wrenches to catch any pressurized fuel that might still be lurking in the lines. Hold the wrench gripping the actual filter and turn the other counter clockwise until the bolt comes out. Remove the fuel line, set the bolt and washers in a safe place, and repeat this step for the other side of the fuel filter.
Use a flat head screw driver to remove the clamp holding the fuel filter in place. Remove the fuel filter from the Cobalt carefully as fuel is still present inside the filter.
Inspect the fuel filter visually for clogs and refit the Chevy Cobalt with a new filter if necessary. Simply reverse the filter removal process to reinstall the old or install a new filter. If the filter is in working order the cause of the fuel delivery problem is a faulty fuel pump.
Remove the fuel pressure gauge and replace the test port cap.
