How Do I Change a Knock Sensor in a Ford 5.4L?

A knock sensor is a piezometric crystal that advances or retards the engine based on load. Knock sensors are typically located on the intake side of the Ford 5.4-liter engine. All knock sensors connect to an electrical wiring harness and links to the vehicle’s On Board Computer (OBC). A knock sensors fails like a light bulb fails – it simply wears out. When a knock sensor does fail, the OBC will automatically retard the engine to minimal fuel efficiency and put the engine in limp mode. The check engine light is a symptom of knock sensor failure.

Step 1 - Disconnect the negative terminal from the vehicle’s battery using the 10- to 12-mm box wrench to prevent short-circuiting while changing out the knock sensor.

Step 2 - Disconnect the electrical wiring harness from the knock sensor by pulling it apart manually or using long-handled needle-nose pliers. This action is similar to pulling a plug out of an electrical wall socket.

Step 3 - Remove the knock sensor by attaching the wobble or swivel bit to the end of the 3/8-inch extension and fastening it to the socket that fits. Insert the socket over the knock sensor. You need the wobble or swivel bit at the end of the extension to access the sensor due to the configuration of the intake manifold.

Step 4 - Connect the ratchet to the end of the 3/8-inch extension that is attached to the wobble or swivel bit and the socket. Use the ratchet to loosen the sensor from the engine block by turning it gently to the left. Remove the defective sensor from the socket and place the defective sensor on the work bench.

Step 5 - Add a dab of white lithium grease to the male end of the electrical connections of the new knock sensor to prevent corrosion build up and to make insertion easier.

Step 6 - Use the socket with the extension to manually screw the new knock sensor to the engine block to avoid cross-threading. Cross-threading occurs when the threads of the sensor do not match up with the threads of the engine block.

Reattach the electrical harness to the sensor and reconnect the negative terminal of the battery.

TIPS: It is best to use hand tools instead of power tools when replacing the knock sensor to avoid cross-threading. When fastening the knock sensor to the engine block, you do not need a lot of torque. Be very gentle so you don’t strip out the threads of the knock sensor. Use a deep well socket to accommodate the electrical lead off the knock sensor.

THINGS YOU'LL NEED: Work bench, 3/8-inch ratchet, Wobble or swivel bit, Six-point deep well socket with a 3/8-inch extension, 10- to 12-mm box wrench, White lithium grease

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