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1999 Ford Ranger P0303 Cylinder 3 Misfire: Diagnosis and Solutions

Model: 1999 ford ranger Fault Code: P0303 Posted: 2011-07-31 12:52

I own a 1999 Ford Ranger with a detected cylinder 3 misfire (OBD2 code P0303). I recently completed a tune-up, and took the vehicle to an auto parts store to have the coil packs tested. They confirmed the coils are functioning properly. Despite this, the misfire persists. I'm now looking for guidance on what other diagnostic steps to take next. The engine is a 2.5L MFI four-cylinder model with dual spark plugs per cylinder and ignition modules located near the intake manifold.

Related fault codes
P0303
Comments (8)
Anonymous 2011-07-31 14:36

Always start by checking compression first, then verify injector pulse and confirm spark presence at the spark plug.

Anonymous 2011-08-05 13:09

I've checked all components—compression is good, injectors show a solid pulse, and there's no spark detected in cylinder 3. The coil packs were tested and passed, but I'm still unsure if the issue lies elsewhere. Could faulty coils be the root cause despite passing tests?

Anonymous 2011-08-05 19:31

What is the exact engine size? How exactly were the coil packs tested—using a dedicated diagnostic machine or a basic tester?

Anonymous 2011-08-06 19:27

The vehicle is equipped with a 2.5L MFI engine. I'm not certain how they performed the coil test—could it be that the testing method isn't reliable? Should I consider replacing the coils as a next step?

Anonymous 2011-08-06 22:29

Is this a 4-cylinder Ford Ranger with two spark plugs per cylinder and an ignition module mounted on the front of the intake manifold? If so, the issue might be related to a faulty ignition module.

Anonymous 2011-08-07 00:32

Yes, it is a 4-cylinder model. It uses dual spark plugs, wiring harnesses, and individual coil packs. The coils are mounted in front of the air filter and intake manifold area.

Anonymous 2011-08-07 09:24

Ah, I've had a similar issue with one of these models—my friend's mother’s Ranger ran very rough due to a failed ignition module. A practical test involves using four inline spark testers (the type that plug between the wire and spark plug and flash a light). Install them in sets—one side at a time—and start the engine. If more than one cylinder shows no spark, especially if they are paired by module or coil, it points to a problem with the ignition module, coil, or wiring. Note: Standard spark testers sold at auto parts stores may not provide accurate results—they can only detect severely faulty components but fail to identify borderline issues. For best results, consider purchasing well-known aftermarket brands like Well's ignition components, which have proven reliable in my experience.

Anonymous 2011-08-08 20:56

Thanks for the detailed advice—I plan to try this spark tester method this week and update with my findings as soon as possible. Appreciate the help!