2006 Chevrolet Impala Miss Fire in Cylinder 4 - Diagnosis and Solutions at 170k Miles
Hello, I'm experiencing a consistent miss fire in Cylinder 4 on my 2006 Chevrolet Impala. I've already checked all common causes including spark plugs, ignition coils, fuel injectors, and engine compression — everything appears to be within normal range. The mechanic recommended inspecting the cylinder heads and suggested possible carbon buildup as a root cause. I've used a fuel cleaner, but it hasn't resolved the issue. The engine runs smoothly for a few days at a time, with vibration disappearing, only for the problem to return shortly after. This vehicle has over 170,000 miles on it, and I'm concerned about whether this is due to wear or a deeper mechanical fault. I'd appreciate any insights from experienced owners or mechanics on how to diagnose and fix this miss fire in Cylinder 4 effectively. Thanks for your help! P.S. The engine is either a 3.5L or 3.9L V6 — could you confirm which one you're referring to? I'm also using AC Delco spark plugs, and compression readings were normal across all cylinders. I haven't tested for vacuum leaks on Cylinder 4 yet — any quick DIY tips (like the spray test) would be very helpful. Also, what was the condition of the #4 spark plug? Was it wet, dry, or black/tan in color? And just to confirm: where is Cylinder 4 located on the engine block (3.5L vs 3.4L configuration)?
You've checked all standard components — good work. Could you clarify if your engine is a 3.9L or 3.5L V6? You have spark to Cylinder 4 and are using AC Delco plugs. What were the compression readings? Have you tested for vacuum leaks on Cylinder 4? Try the spray test (spray carburetor cleaner near the intake hose) — it's quick and effective. How did you check the fuel injector? Swapping injector locations is a common diagnostic method, though it's difficult to perform. What was the condition of the #4 spark plug — wet, dry, or black/tan? And just to confirm: where exactly is Cylinder 4 located on the engine (3.5L or 3.-4L configuration)? This helps ensure we're discussing the same setup.