P0303 Misfire Diagnosis and Repair for 2002 Chevrolet Tahoe - Fuel Injector or Ignition System?

I'm facing the same issue on my 2001 Ford F-150—started with a cylinder 5 misfire, then progressed to cylinder 7. The idle is also rough at times. Any suggestions for diagnosing or fixing this?

It sounds like the 2002 Tahoe may be experiencing an underlying engine-related issue that requires a more thorough diagnosis beyond basic component replacements.

I recently encountered identical symptoms on my 2003 Chevrolet Silverado with a 5.3L V8 and 63,000 miles. I used to drive it regularly, but after switching to a 'beater' Saturn for commuting, the truck sat idle in the garage for two weeks. Last week, after driving it again, the check engine light came on and began flashing—indicating a misfire. A code scan revealed P302 (misfire in cylinder 2). I replaced the spark plugs with AC Delco Iridiums, which didn't resolve the issue. Cylinder 2 showed signs of fouling compared to others. I then installed a new coil pack for cylinder 2—still no improvement. After replacing all plug wires, the misfire persisted. I swapped injectors between cylinders 2 and 4, which triggered a P0300 (multiple cylinder misfire), suggesting an injector issue. To address this, I used Seafoam by disconnecting the vacuum line to the brake booster and directly injecting it into the intake manifold. It produced heavy smoke, requiring throttle feathering to prevent stalling. After using up the entire can, the misfire disappeared—though a steady check engine light remains. I suspect the smoke caused temporary sensor interference and hope the code will clear after continued driving. I'm not sure if this method is extreme, but several sources have reported similar results with positive outcomes. I'll visit the parts store tomorrow to re-scan for any returning codes.

That solution didn't last—this morning when I started the truck, the misfire returned. A new scan shows a P304 code (misfire in cylinder 4). Since the injector was moved from cylinder 2 to 4 and the original misfire was in cylinder 2, this strongly suggests that the injector in cylinder 4 is faulty. I'm planning to replace it with a genuine OEM unit.

When dealing with P0300 or P0303 codes—especially on multi-cylinder engines like the 6-cylinder or V8 setups—it's critical to systematically rule out potential causes before replacing parts. Recommended steps: 1. Perform a basic tune-up if needed (spark plugs, wires, distributor cap, rotor). 2. Verify fuel pressure is within specifications. 3. Check for engine vacuum leaks—common at intake gaskets or hoses. 4. Test individual fuel injectors for proper operation. 5. Evaluate internal engine wear and compression levels in affected cylinders. A methodical approach helps avoid unnecessary part replacements.

Older vehicles like the 2002 Tahoe are prone to fuel leaks from injector lines under the intake plenum and vacuum leaks at intake gaskets. Additionally, aftermarket distributor caps often perform poorly compared to OEM parts—this should be considered when troubleshooting ignition-related issues.