P0302 on Lincoln: How to Diagnose & Fix

The 5.4L 3-valve Triton V8 in 2005-2008 Navigator (and shared F-150/Expedition) uses a two-piece spark plug (Motorcraft SP-515/SP-546) that frequently snaps off in the cylinder head during removal. The lower portion stays welded into the head by carbon, leaving the upper electrode in the socket. Common at 60,000-100,000 miles when the first plug change is attempted.

Second- and third-generation Navigators with the 5.4L 3-valve Triton V8 use a unique two-piece spark plug whose long electrode shell extends below the threads. Carbon deposits cake into the gap over high mileage, gripping the plug so tightly that the shell breaks off during removal, leaving a portion seized inside the aluminum cylinder head. This turns a routine tune-up into a costly extraction job.

Second-generation MKZ models equipped with the 2.0L EcoBoost turbo engine can develop an internal coolant leak where coolant seeps from the cooling jacket into a combustion chamber, commonly cylinder 2. This is attributed to a cylinder head/block design and sealing defect. Burned coolant causes misfires, white exhaust smoke, chronically low coolant with no external leak, and in severe cases overheating and complete engine failure. The defect is the subject of a Ford EcoBoost coolant-intrusion class action.

2016-2017 Lincoln MKX models with the 2.7L EcoBoost V6 (engines built roughly April 2016 to January 2017) can suffer excessive oil consumption caused by defective cylinder head valve guides that let oil seep into the combustion chamber and burn off. Owners report burning roughly a quart every 3,000 miles, often accompanied by rough idle, misfires, and blue/white exhaust smoke. Ford addressed this in Technical Service Bulletin 19-2243, whose official remedy is replacement of both left and right cylinder heads. Fouled spark plugs from oil contamination commonly trigger cylinder-specific misfire codes.

The 1998-up 4.6L 2V V8 uses eight individual coil-on-plug ignition coils whose boots and towers crack with age and heat, allowing spark to track to ground and causing single- or multi-cylinder misfires, rough idle, and stumbling under load. Failures are accelerated when the 1996-2001 plastic intake manifold leaks coolant into the spark plug wells and shorts the coils. It is one of the most common drivability complaints on the platform, well documented across owner forums and diagnostic guides.

2019-2020 Nautilus models with the base 2.0L EcoBoost (non-hybrid) suffer unexplained coolant loss, white tailpipe smoke, an overheat warning, and sometimes coolant intrusion into the cylinders. Ford TSB 20-2234 traces the most common cause to a failing exhaust gas recirculation (EGR) cooler that leaks coolant internally; the related design also has a known coolant-intrusion weakness (narrow coolant slit between cylinders compromising the head-gasket seal). Owners report repeated coolant top-offs with no visible external leak, then misfires as coolant fouls the plugs. A June 2025 Ford EcoBoost coolant-intrusion class action covers 1.5L-2.0L engines; the most severe Nautilus cases require engine replacement with the redesigned block.