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MikeD', Technician
Category: Car
Satisfied Customers: 696
Experience:  ASE Cert, AS Degree in Automotive Diagnostics
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1996 saturn: Service Engine Soon..code PO303- misfire on #3 cylinder

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I have a 1996 Saturn SL2. I have a hard failure- Service Engine Soon Light continously flashes. I have a code that keeps resetting- code PO303- misfire on #3 cylinder. I have replace both coil packs, plugs andf wires- all parts new. Still code keeps resetting, car idles, and runs rough, not to mention uses a ton more gas.

There could be a couple of things causing this to happen. You mention that it uses allot more gas so I am leaning toward a leaking injector. But It could also be compression loss from a bad head gasket or worn piston rings. First I would do a compression test and cyl leakage test on the motor to test the compression. Then pull the injector to check the condition of it. If you keep driving the vehicle you will damage the catalytic converter due to excess hydrocarbons being introduced.

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Customer: replied 9 years ago.
I think it is more of an electrical, rather than a mechanical. The car ran perfectly fine one day, then the next morning it was raining, and cool, I started the car, and immediatly the light began to flash, and car ran rough. I see no signs of head gasket leakage in oil, anti-freeze or exhaust, but I admit it may be an injector. If by chance it isn't the injector, where do I look from there?

Check the plug and compare it to the other plugs. The plug will be darker then the others from fuel foul. Next check it electrically with a noid light. If the pulse is good then you will need to remove it. Swap it to a different cyl, See if the problem goes to the other cyl. If so, replace the injector.