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P0302 Misfire Diagnosis and Repair on 2002 GMC Suburban with 5.3L Engine

Model: 02 Suburban Fault Code: P0302 Posted: 2015-02-07 23:31

My 2002 GMC Suburban (5.3L V8) has been running well for over 240,000 miles, but recently the check engine light began flashing when driving over 30 mph—remaining off at lower speeds. The OBD2 code P0302 indicates a misfire in cylinder 2. I've already replaced the spark plugs, ignition wires, and the coil pack, yet the issue persists. Upon inspection, there is no spark detected at cylinder 2. Despite these efforts, the engine continues to exhibit a severe misfire without noticeable power loss. What could be causing this? Is P0302 common on 5.3L engines, and what are the next steps for diagnosis?

Related fault codes
P0302
Comments (8)
Anonymous 2015-02-08 05:58

I have a 2002 GMC Suburban with 225,000 miles and it's still performing well. However, I'm now experiencing a misfire that triggers the check engine light. A scan at AutoZone confirmed P0302. I've replaced both spark plugs and ignition wires—no improvement. The issue only appears when driving over 30 mph; below that speed, the light stays on. When I pulled the spark plug wire from cylinder 2, there was no change in behavior. Any advice would be greatly appreciated.

Anonymous 2015-02-08 10:24

A flashing check engine light is a serious warning—it may indicate potential catalytic converter damage. P0302 points to a misfire in cylinder 2. You mentioned no change when removing the spark plug wire from cylinder 2—this suggests either no ignition or poor fuel delivery. First, confirm spark at cylinder #2 (first plug on passenger side). Did you use AC Delco plugs? Plug color and condition (wet, dry, black, tan) can provide clues. Next, consider fuel injector issues—the 5.3L engine has a spider-type fuel injector assembly inside the intake manifold. Try adding one bottle of TECHRON or SEAFOAM to the fuel system. Finally, perform a compression test on cylinders 2 and 4. I suspect no spark at cylinder #2—please confirm.

Anonymous 2015-02-08 22:57

I'm planning to run a compression test tomorrow. The spark plugs are AC Delco type, but I've confirmed there's no spark in cylinder 2. I'll update you on the results. Is this a common issue with 5.3L engines? It doesn't feel like a major power loss—just a persistent misfire that needs urgent attention.

Anonymous 2015-02-09 08:54

Misfires are common across all engine types—not unique to 5.3L engines. However, I made an error earlier—I assumed this was a 5.7L model. Thank you for clarifying—it's actually a 5.3L, which makes troubleshooting easier. For a 5.3L, try swapping the coil from cylinder 2 with that of cylinder 4. If the misfire moves to cylinder 4, it likely points to a faulty coil. Let me know the result after testing.

Anonymous 2015-02-09 23:01

I'll test by swapping coils between cylinders 2 and 4 to see if the misfire shifts. I'm also planning to run a fuel treatment (SeaFoam) through the system tomorrow. I'll keep you posted on progress—thank you for your guidance!

Anonymous 2015-02-14 21:15

Here's my update: Due to bad weather, I’ll have to delay testing for a few days. After troubleshooting, I discovered that the issue was actually a faulty coil pack (not just a coil). I replaced it and now there is spark in cylinder 2. However, the misfire remains. The spark plug pulled from cylinder 2 showed heavy wetness and dark color—indicating possible fuel delivery issues. I’m planning to replace the fuel injector and install new spark plugs as next steps. I’ll update again once complete—thank you all for your help!

Anonymous 2015-02-15 13:31

Note: The 5.3L engine uses individual coils—one per cylinder—not a shared coil pack. Since there is now spark at cylinder #2, consider installing an AC Delco plug in that position to ensure proper performance. Add fuel treatment and monitor the system closely. Recheck for P0302 after operation.

Anonymous 2015-03-11 21:18

Final update: I’ve completed all diagnostics—compression test, coil replacement, spark plug change, and fuel injector replacement. After these repairs, my 2002 Suburban runs smoothly with no misfire or check engine light. Thanks to everyone for your expert advice—this repair would not have been possible without this community support. Truly appreciate it!