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2001 Chevrolet Suburban P0300 Code: Misfire on Cylinders 5 and 6 - Diagnosis & Solutions

Model: 2001 chevrolet suburban Fault Code: P0300 Posted: 2011-07-17 17:07

I own a 2001 Chevrolet Suburban with a 5.3L engine that is showing a P0300 fault code indicating a random misfire, specifically affecting cylinders 5 and 6. I've already performed several repairs: swapped both fuel injectors and ignition coils, confirmed good compression (175 psi), replaced the crankshaft position sensor, and completed a relearn procedure. The issue persists exclusively on cylinders 5 and 6. I also replaced both primary oxygen sensors, temporarily unplugged them to enter base mode, and changed the intake gasket—all without resolving the misfire. Fuel pressure is stable at 52 psi, and the fuel filter has been replaced. Despite these efforts, the P0300 code remains active. What other diagnostic steps or potential causes should I consider? Any known issues with this model year regarding cylinder-specific misfires?

Related fault codes
P0300
Comments (4)
Anonymous 2011-07-17 18:45

The fuel pressure regulator on the intake manifold spider might be leaking, or the distributor could be faulty. In older GM trucks like the 2001 Suburban, worn distributor bushings are known to cause misfires specifically in cylinders 5 and 6—this is a common issue when the distributor assembly is compromised.

Anonymous 2011-07-28 23:04

Correction: The 2001 Chevrolet Suburban uses a coil-on-plug (COP) ignition system, not a traditional distributor. It features individual coils mounted directly above each spark plug. I've confirmed that both injectors and coils have been swapped, the crankshaft sensor has been replaced, and the P0300 code persists exclusively on cylinders 5 and 6.

Anonymous 2011-07-29 20:01

I recommend using a noid light to check for injector pulse. A lack of signal from the Powertrain Control Module (PCM) could indicate an internal PCM driver issue or wiring fault affecting only cylinders 5 and 6.

Anonymous 2011-07-29 20:55

Apologies for the earlier confusion—while the truck uses a coil-on-plug system, the camshaft position sensor is still mounted in the same location as the old distributor. Worn or improperly seated camshaft bearings can cause misfires in cylinders 5 and 6. The noid light suggestion is excellent—verify fuel pressure integrity and check for vacuum leaks on the intake manifold. Are the spark plugs wet when removed? Additionally, some GM engines from this era have known valve guide and valve face sealing issues that may pass compression tests but still cause misfires.