1999 Pontiac Sunfire PO303 Code - Cylinder #3 Misfire: Coil or Coil Cover? | No Start Diagnosis
My 1999 Pontiac Sunfire with a 2.4L engine has suddenly stalled and will not start. The onboard diagnostic system shows a PO303 code indicating a misfire in cylinder #3. Possible causes include a faulty ignition coil or damaged coil cover. I'm wondering if a single bad coil could cause multiple misfire codes — for example, would a failing coil result in more than one misfire detection? Given that the engine now won't start at all, I suspect deeper issues such as loss of compression or injector signal. Before replacing any components, I'd like to confirm whether spark is present and properly generated from the ignition system.
It's not always necessary to have multiple misfire codes for a single faulty coil — in my case, a 2000 Cavalier with the same engine setup had only a cylinder #2 misfire due to a failing ignition coil assembly. I experienced no stalling or complete no-start issues, just rough idle and reduced fuel economy. The design of this engine makes spark testing tricky, but here's a practical method: purchase 18-inch ignition wires (commonly found in imported 4-cylinder engines), connect one wire between the coil boot and each spark plug, then use an inline spark tester or timing light to check for proper spark. This allows you to verify if the coil is firing correctly without replacing an expensive module. I recommend using a used part or components from Wells Automotive — their site offers detailed listings of compatible parts. As always, perform compression tests and injector pulse checks before replacing any ignition components.