← Back to list

P0304 Misfire Diagnosis and Fix for 2009 GMC Acadia SLT 3.6 - Intermittent Cylinder 4 Issue

Model: 2009 GMC Acadia SLT Fault Code: P0304 Posted: 2015-02-01 10:40

I own a 2009 GMC Acadia SLT 3.6 with a persistent P0304 misfire code on cylinder #4. The issue is intermittent—sometimes no symptoms for weeks, then suddenly the engine starts misfiring specifically in cylinder 4. I've already replaced both the coil and spark plug for cylinder 4, which provided only temporary relief. The problem remains consistent with the same P03

Related fault codes

P0304

Comments (2)

Anonymous 2015-02-01 12:46

Replacing the ECM is not a common or recommended first step. Is your vehicle stock (only GM parts)? What does your OBD2 scanner show? Does it read all stored codes and provide live data? Cylinder #4 is located on the front bank, center position. Let's start with simple, low-cost fixes: - Add one bottle of 'Sea Foam' or 'TECHRON' fuel system cleaner. - Check the coil connector and injector connector for tightness and signs of corrosion. - What does your spark plug look like? Wet, dry, black, or tan? These are key indicators that can help pinpoint whether it's a fuel delivery, ignition, or sensor issue.

Anonymous 2015-02-01 20:09

Thanks for the helpful advice! I misunderstood cylinder numbering earlier—I thought cylinders 2, 4, and 6 were on the firewall side. After replacing the coil and plug, I noticed a vacuum line above cylinder 4 was loose and leaking. I tightened it by hand three full turns and now it's secure. I completed a test drive of about 25 miles with no misfires so far—this is promising. However, since this issue has come and gone before, I suspect there may be an underlying electrical or fuel system problem. Thanks again for the guidance!