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2003 Jeep Liberty Renegade 3.7L V6 P0306 Misfire: Diagnosis and Solutions

Model: 2003 Jeep Liberty Renegade Fault Code: P0306 Posted: 2007-04-19 12:10

I've been consistently receiving a P0306 diagnostic trouble code (cylinder 6 misfire) on my 2003 Jeep Liberty Renegade with the 3.7L V6 engine. The vehicle cranks repeatedly—sometimes for several minutes—if I let it idle and then try to start again, eventually firing up. Once running, it often sputters or runs roughly, resembling a carbureted engine before stabilizing. I've already tried replacing the spark plugs from NGK V-Power to Autolite Copper, which didn't resolve the issue. I swapped the #6 coil with the #3 coil—this prevented starting entirely. When I switched the #3 coil with the #1 coil, it started but ran poorly. I then replaced the #1 coil (originally installed in cylinder 6) and now the P0306 code persists. Upon removing the #6 spark plug, I noticed a small amount of oil on the top threads where the socket engages—the rest of the plug and threads appear clean and normal in color. A friend suggested a possible camshaft or crankshaft position sensor failure, but I'm not certain. I only have powertrain warranty coverage due to it being certified pre-owned, and diagnostic services are priced at $45/hour—seems high for reliable drivability assessment. I haven't yet performed a compression test. If anyone has experience with this specific model or similar misfire issues, any insights would be greatly appreciated. I'm open to testing injectors or using tools like a noid light to verify injector pulse signals before further troubleshooting.

Related fault codes
P0306
Comments (4)
Anonymous 2007-04-19 16:03

A $45 diagnosis for drivability-related issues is likely excessive and may not involve qualified technicians. Start with the correct spark plugs for your engine model, and ensure compression testing is performed. I've seen camshaft failures on 3.7L engines and injector clogging as common causes. Try swapping the #6 fuel injector to a different cylinder (e.g., cylinder #1) to see if the P0306 code changes—only after confirming good compression. A flat cam lobe might not show up in a standard compression test. Crankshaft or cam position sensors can fail, but they typically don’t produce isolated misfire codes and are prone to breaking off inside the engine. I’ve worked on enough Liberty models to know this engine isn't one of my favorites.

Anonymous 2007-04-19 16:09

Compression test results show consistent 150 psi across all cylinders, with variation within ±2–3 psi. A leak-down test wasn’t possible due to lack of proper equipment—the compression tester requires a sealed cylinder setup. I plan to remove the #6 fuel injector and swap it with the one on cylinder #1 (opposite side) to see if the P0306 code shifts to another cylinder—this would help confirm whether an injector is faulty. The spark plugs have around 2,000 miles on them; only the #6 plug shows oil on its threads. The rest of the plug appears clean and normal in color. Other plugs show a slight ash-gray tip, with bright white center electrodes indicating proper spark. While the engine starts fine now, I know there's an underlying issue.

Anonymous 2007-04-19 16:31

Before removing or swapping the #6 injector, use a noid light to confirm that the Powertrain Control Module (PCM) is actually sending a pulse signal to the injector. This ensures the issue isn't due to lack of ignition or fuel command.

Anonymous 2007-04-19 16:35

I don’t currently have a noid light, but I can rent one or purchase it—it's around $40 for a complete kit and would be useful for verifying injector signal integrity.