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Buick Regal GS Supercharged - P0303 Misfire at 124,000 Miles: Plug Wire or Coil Issue?

Model: Buick Regal GS Fault Code: P0300 Posted: 2010-10-02 12:25

My 1998 Buick Regal GS supercharged vehicle has reached over 124,000 miles and recently triggered the 'Service Engine Soon' light with a P0303 diagnostic code indicating a misfire in cylinder 3. Initially, we observed a misfire occurring during cycle 4. To troubleshoot, we swapped the spark plug wires between cylinders 3 and 4 — after which cylinder 3 began misfiring, leading us to suspect faulty plug wires. We have since replaced all spark plug wires with new ones, but the P0300 code (cylinder 3 misfire) continues to appear in the system. We recently identified and repaired a fuel line leak, which we believe was unrelated to the cylinder-specific misfire. However, given that the issue persists only on cylinder 3 after wire replacement, we are now considering whether the problem lies with the ignition coil or the spark plug module. The vehicle runs normally without overheating or water usage issues. What could be causing this persistent misfire in cylinder 3? Are there other common causes such as a faulty injector, burnt valve, vacuum leak, or defective spark plug that should be ruled out?

Related fault codes

P0300P0301

Comments (5)

Anonymous 2010-10-02 15:38

Try swapping the ignition coils on the coil pack module. If the misfire moves to another cylinder after switching, it's likely a faulty coil. Both ignition coils and modules are known common issues in older Buick Regal GS models.

Anonymous 2010-10-03 13:41

Thanks for the tip! We'll try swapping the coils on the module and monitor the results closely.

Anonymous 2010-10-28 12:02

Jeff Compton wrote: Try swapping the ignition coils on the module. If the misfire moves, it's likely a faulty coil. Both coils and modules are known common issues in Buick Regal GS models. Hi Jeff — I just wanted to confirm: we've swapped the coils around, but the misfire still occurs only in cylinder 3. Given that the issue remains localized, does this point toward a failing module? Would replacing the spark plug module be necessary? Thanks for your insight!

Anonymous 2010-10-28 18:56

While it's possible the module is at fault, it's important to consider other potential causes of individual cylinder misfires — such as a clogged fuel injector, faulty injector circuit, burnt valve, head gasket leak, vacuum leaks, or worn spark plugs. These factors should all be systematically ruled out before concluding that the issue is with the module.

Anonymous 2010-10-28 19:04

Let's hope it's the module. My wife mentioned that her Buick Regal GS sometimes throws a misfire code after driving uphill — possibly due to increased load and pressure on the ignition system. The vehicle has new plugs, wires, and coils installed, and runs normally without overheating or water usage issues.