GM engine code P0303

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 In this page you will learn how to diagnose a GM code P0303 in a chevy Cavalier, this code is part of the OBD II and it will appear on most GM cars, trucks and SUV's, if you pay attention to the steps in this page, you should be able to diagnose the problem in your GM vehicle regardles of model.

The vehicle we are working on is a 1997 Chevrolet Cavalier equipped with a 2.2 L engine.

The owner brought the car to our shop complaining of a hesitation/vibration, at idle and under acceleration, this is what we found............














 We scanned the car and we found the Engine trouble code P0303 " Cylinder 3 misfire". This was a good starting point to begin troubleshooting the cause of the engine misfire.

 We checked for spark at #3 spark plug wire with a spark tester ( see image ) the car had normal spark, we removed the spark plug to make sure that it wasn't fouled,the spark plug didn't show any signs of abnormal wear meaning that the misfire was not being caused by either the spark plug or the spark plug wire.

We used an automotive stethoscope to listen at all 4 injectors, we couldn't hear #3, the problem was either the injector or lack of signal from the ECM.
 To make sure that the injector was getting its signal from the ECM, we used  a noid light ( see image ) to test for injector signal at #3 injector electrical connector.

The signal was normal, our misfire was being caused by a bad injector, the strange part in this particular car is that this type of fuel injectors when they start malfunctioning they start leaking fuel, but this particular one didn't.

 The first step is relieve the fuel pressure from the system, the easiest way to do it in this vehicle is by removing the fuel pump fuse and run the engine till it runs out of fuel, next unplug the negative battery cable.

 To gain access to the Injector it is necessary to remove the throttle cable bracket, undo the cables, remove the bolts that fasten the bracket in place and set it aside.

 Remove the idle adjusting screw to gain clearance.

 Slide the hise clamp back and unplug the vaccum hose as shown in the picture.

 Unplug the electrical connectors from #3 and #4 fuel injectors.

 Remove the two screws that secure the fuel injector retaining bracket in place.






 Gently, slide the bracket out as shown in the picture.

 Pay close attention to the direction the fuel injector is facing, this is very important because the retaining bracket allows the injectors to be facing in one direction only.

Using a long flat screwdriver gently pry the fuel injector out, place a towel underneath to catch the gasoline that will spill out when you pull the injector out.

Lubricate the seals in the new fuel injector with petrolleum jelly, install the remaining components in the reverse order you took them off.

Connect the negative battery cable back on, install the fuel pump fuse back and start the engine, check for fuel leaks, if you did everything correctly there shouldn't be any fuel leaks.

  Take the car for a test drive, the car should idle smooth and it shouldn't hesitate under acceleration. When you come back from test driving the car, open the hood again, double check for fuel leaks