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2010 Ford Navigator 5.4L Engine Misfire: P0300, P0302, P0308 with Intermittent Symptoms

Model: 2010 Navigator 5.4L Fault Code: P0302 Posted: 2019-11-18 10:35

I recently installed a new engine in my 2010 Ford Navigator 5.4L and have been experiencing recurring misfiring issues ever since. The problem only occurs while driving at highway speeds—after approximately 15 to 30 minutes of sustained driving, the check engine light begins flashing and the engine runs roughly for about 15 seconds before returning to normal operation. This cycle repeats intermittently, sometimes occurring after as much as 30 minutes of driving. The issue does not happen during city or non-highway driving conditions. The diagnostic trouble codes that appear are P0300 (multiple cylinder misfire), P0302 (cylinder 2 misfire), and P0308 (cylinder -than misfire). The engine light resets itself after a few days of normal local driving. I have already replaced all spark plugs and coils, which were nearing 100,000 miles—this did not resolve the issue. When taken to a repair shop, technicians are unable to reproduce the misfire because it may take up to an hour for the condition to manifest, making consistent testing impossible. This intermittent nature makes diagnosis particularly challenging. I am seeking advice on potential root causes and solutions that could help identify or fix this recurring problem.

Related fault codes
P0302P0308
Comments (2)
Anonymous 2019-11-19 09:12

This appears to be an intermittent misfire issue. Try manually wiggling the wiring and connectors for cylinders 2 and 3 while driving to check for loose connections or damaged harnesses.

Anonymous 2019-11-20 04:30

P0300 indicates random cylinder misfiring, which often points to a lean fuel condition—too much air relative to fuel. This issue is especially noticeable during highway driving and may occur after the engine has warmed up from idle or choke mode. Possible causes include an air leak in the intake manifold system (due to mechanical wear or faulty components), a malfunctioning sensor or actuator, or a loose multi-plug connection. Since this misfire only occurs under specific conditions—such as highway cruising—it's important to identify when and where it happens (e.g., uphill driving with high engine load). Intermittent faults like this are difficult to diagnose without real-world driving replication. Please consider checking for vacuum leaks or inspecting intake system components, especially around cylinder 2 and 8, which are flagged in the codes.