Ranger 4WD V6-245 4.0L VIN X SFI (1999)
7. Inspect for normal burning.
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Check for light tan or gray deposits on the firing tip.
8. Inspect for pre-ignition, identified by melted electrodes and a possibly damaged insulator. Metallic deposits on the insulator indicate engine
damage. This may be caused by incorrect ignition timing, wrong type of fuel, or the installation of a heli-coil insert in place of the spark plug
threads.
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Install a new spark plug.
9. Inspect for overheating, identified by a wire or light gray-brown spots with a bluish-burnt appearance of electrodes. This is caused by engine
overheating, wrong type of fuel, loose spark plugs, spark plugs with an incorrect heat range, low fuel pump pressure, or incorrect ignition timing.
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Install a new spark plug.
10. Inspect for fused deposits, identified by melted or spotty deposits resembling bubbles or blisters. These are caused by sudden acceleration.
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Clean the spark plug.