2013-2018 Nissan Altima 2.5L QR25DE spark plug replacement

Let the engine sit until it is fully cool to the touch on the cylinder head. Aluminum head threads are soft, and pulling plugs from a hot head is how threads strip. This is not a shortcut worth taking.

Open the hood and pull the 10mm negative terminal off the battery. This prevents the ECM from logging misfire codes when coils are disconnected and eliminates any risk of a stray injector pulse while a plug well is open.

Two rubber grommets snap the plastic cover onto studs at the front of the intake manifold. Pull the cover straight up firmly with even pressure on both sides. There are no fasteners.

Four coil-on-plug coils sit in a row along the top of the valve cover. Each has a small locking connector. Press the tab on the harness clip and lift the connector off each coil. Route the harness away from the coil so it does not fall back onto the plug well while working.

Each coil is held to the valve cover by a single 10mm bolt at its base. Loosen and remove the bolt, then twist the coil a quarter turn to break the boot seal on the plug and lift it straight out. Set the coils in order so they return to the same cylinders. Do not pull coils by their harness pigtail - the internal connection to the coil winding pulls apart and creates an intermittent misfire that only shows up under load.

Blow compressed air into each plug well briefly, or vacuum with a small crevice attachment. Debris in the plug well falls into the cylinder the moment the plug is removed, and even a small grain of grit can score the cylinder wall.

Fit the 5/8 inch plug socket with rubber insert onto the first plug and turn counterclockwise with the ratchet and extension. Once loose, spin the plug out by hand with the extension so the plug seats squarely in the socket for lifting. Inspect each plug as it comes out - even, tan coloring across all four indicates healthy combustion. Oil-fouled tips point to valve stem seal wear or PCV issues. White chalky electrodes point to a lean condition worth investigating before installing new plugs.

The PLZKAR6A-11 ships pre-gapped to 0.043 inch (1.1mm). Confirm the gap with a wire feeler on each plug before installation. Do not use a coin-style gap tool on the precious-metal center electrode - it will chip the platinum tip. If the gap needs adjustment, tap the ground strap gently on a clean surface to close, or slide a feeler under the strap and lift to open.

Do not apply anti-seize. Nissan's OE plug threads are pre-coated at the factory, and additional compound changes the effective torque. Thread each plug in by hand from the extension until it stops. Fit the ratchet and torque the spark plugs to 18 ft lbs (25 Nm). Verify against your service manual. Overtightening cracks the porcelain insulator; undertightening allows combustion gas past the sealing washer and burns the electrode prematurely.

Squeeze a pea-sized dab of dielectric grease inside each coil boot and spread it thinly around the boot interior with a clean finger. This makes the boots slide off cleanly at the next service and prevents electrical tracking down the porcelain.

Set each coil into its plug well and press down to seat the boot onto the plug terminal. Start the 10mm hold-down bolt by hand, then torque the coil hold-down bolts to 89 in lbs (10 Nm). Verify against your service manual. Reconnect the harness clip until it clicks positively.

Press the appearance cover down onto its two grommets. Reconnect the 10mm negative battery cable and torque it snug (do not overtighten - the terminal is soft lead).

Start the engine. It may crank half a second longer than usual as the ECM re-establishes its idle strategy. Idle should smooth out within thirty seconds. No misfire codes, no CEL, and no rough idle at temperature is the confirmation that all four coils and plugs seated correctly.