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Misfires on GM vehicles

Fix codes P0300 P0301 P0304 Misfire on cylinder 1 on left turns, misfire on cylinder 4 on right turns on GM vehicles

GM has issued a technical service bulletin (TSB) PIP3333A to address Misfires on GM vehicles problems with the cylinder misfires on certain cylinders. The problem can occur on cylinder #1 on left turns, and cylinder #4 on right turns. The bulletin applies to the following vehicles:

2004-2008 Chevrolet Aveo
2004-2006 Chevrolet Cavalier
2005-2008 Chevrolet Cobalt, Cobalt SS
2006-2008 Chevrolet HHR
2004-2008 Chevrolet Malibu
2007-2008 Pontiac G5
2006-2008 Pontiac G6
2005-2006 Pontiac Pursuit (Canada Only)
2004-2006 Pontiac Sunfire
2003-2008 Pontiac Vibe, Vibe GT
2003-2008 Saturn Ion, Ion Redline
2007-2008 Saturn Aura, Aura Hybrid
2004-2008 Saturn Vue
2007-2008 Saturn Vue Hybrid with a 4 Cylinder Engine

The misfire causes rough running and can last as long as 10 seconds. The misfire can set off the check engine light and result in trouble codes P0300, P0301, P0304 if the misfire lasts long enough or occurs often enough. GM has linked this problem to fuel contamination. The problem occurs in certain cylinders and not all because these vehicles employ a returnless fuel system. The fuel is pumped up to the fuel rail and unlike a return fuel system where excess fuel is returned to the tank, all the fuel stays in the fuel rail. If the fuel is contaminated with rust or other particles, it is far more likely to block fuel injectors for cylinders #1 or #4. That explains why the misfire happens on left or right turns—the particles float to those ends of the fuel rail and block fuel, causing a misfire.

The only fix for this problem is to remove the fuel rail (with fuel still in it) and drain it into a clear container. Do not try to obtain a sample from the test port—it will most likely show no particles. If you find contamination, clean the fuel system using the “Fuel System Cleaning” procedure in the shop manual and clean the inside of the fuel tank, fuel lines, and fuel rail.

© 2012 Rick Muscoplat

Posted on by Rick Muscoplat

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