Sierra Knock Sensor 18-7703, Replaces 3854512, for Mercruiser GM V8 454/502/540/572 CID and Volvo Penta 7.4L/8.2L OMC Stern Drive

The Sierra 18-7703 Knock Sensor is a direct-fit replacement engine sensor built for Mercruiser GM V8 stern drive engines (454, 502, 540, and 572 CID) as well as Volvo Penta 7.4L and 8.2L and OMC stern drive applications from 1999-2001. This sensor detects abnormal detonation (knock) inside the engine and sends that signal to the ECU so ignition timing can be adjusted, protecting the engine from damage caused by pre-ignition. It is constructed from metal for durability in the marine engine bay environment, with a measuring range of 60 to 120 dB to accurately pick up knock vibration across normal operating conditions. Each package includes one knock sensor, sized at a compact 0.39 x 0.39 x 0.39 inches for easy installation in the factory sensor location. As a Sierra product, it is engineered to meet or exceed the performance of the original equipment sensor it replaces, giving boat owners and marine technicians a reliable option for maintenance or repair work. The 18-7703 is a straightforward bolt-in replacement for the OEM 3854512 knock sensor, making it a practical choice when servicing GM V8 based stern drive powerplants across Mercruiser, Volvo Penta, and OMC applications.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-7703
• Category: Volvo Penta Fuel Injectors & Knock Sensors
• UPC: 808282287429
• Weight: 0.26 pounds
• Material: Metal
• Item Dimensions: 0.39 x 0.39 x 0.39 inches
• Measuring Range: 60 - 120 dB
• Fit Type: Universal Fit
• Package Quantity: 1 knock sensor
• Compatible Engines: Mercruiser GM V8 454, 502, 540, and 572 CID; Volvo Penta 7.4L/8.2L and OMC stern drives (1999-2001)

Fitment

• Mercruiser GM V8 engines: 454, 502, 540, and 572 CID
• Volvo Penta 7.4L and 8.2L stern drives
• OMC stern drives (1999-2001)

Replaces (OEM)

• 3854512

Frequently Asked Questions

What engines does the Sierra 18-7703 knock sensor fit? The Sierra 18-7703 knock sensor is built for Mercruiser GM V8 engines in the 454, 502, 540, and 572 CID range, as well as Volvo Penta 7.4L and 8.2L stern drives and OMC stern drives from 1999-2001.

What OEM part number does the 18-7703 replace? It replaces OEM part number 3854512, making the Sierra 18-7703 a direct bolt-in substitute for that original knock sensor.

How many sensors come in a package? One Sierra 18-7703 knock sensor is included per package, ready to install in place of the original sensor.

What is the knock sensor made of? Metal construction is used for the Sierra 18-7703, giving it the durability needed to hold up in the marine engine compartment.

What size is the Sierra 18-7703 knock sensor? It measures 0.39 x 0.39 x 0.39 inches, a compact size designed to fit the factory sensor mounting location.

What detonation range can the sensor detect? The 18-7703 has a measuring range of 60 to 120 dB, allowing it to pick up abnormal engine knock across typical operating conditions.

Is the Sierra 18-7703 a genuine OEM part or an aftermarket replacement? The 18-7703 is a Sierra aftermarket replacement sensor engineered to meet or exceed the performance of the original 3854512 equipment sensor it replaces.

Will this knock sensor work on a Volvo Penta stern drive? Yes, the Sierra 18-7703 is designed for Volvo Penta 7.4L and 8.2L stern drive engines in addition to Mercruiser GM V8 and OMC stern drive applications.

How much does the 18-7703 knock sensor weigh? The Sierra 18-7703 weighs 0.26 pounds.

What does a knock sensor do on a marine engine? A knock sensor like the Sierra 18-7703 detects abnormal detonation vibrations in the engine and signals the ECU to adjust ignition timing, helping prevent engine damage from pre-ignition.

Does the 18-7703 fit OMC stern drives? Yes, the Sierra 18-7703 is designed for OMC stern drives from 1999-2001 in addition to its Mercruiser and Volvo Penta applications.