{"product_id":"mercury-mercruiser-ignition-coil-8m0178581-496-mag-8-1l","title":"Mercury MerCruiser Ignition Coil 8M0178581 — 496 MAG \/ 8.1L | Design II","description":"\u003ch2\u003eMercury MerCruiser Ignition Coil 8M0178581 — 496 MAG \/ 8.1L | Design II\u003c\/h2\u003e\u003cp\u003eThis genuine OEM ignition coil is the later Design II unit used in the cylinder-head ignition system on selected MerCruiser 496 MAG and 8.1L inboard engines. Each coil fires one cylinder directly, so a full V8 application requires 8 coils. If your engine is misfiring, running rough on a specific cylinder, or throwing an ignition-related fault, this is the OEM replacement to reach for — once the affected cylinder and coil have been properly diagnosed.\u003c\/p\u003e\u003ch2\u003ePart Information\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eOEM Part Number:\u003c\/strong\u003e 8M0178581\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eBrand:\u003c\/strong\u003e Mercury \/ MerCruiser\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eOfficial Product Type:\u003c\/strong\u003e Ignition coil (Design II)\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eSupersedes:\u003c\/strong\u003e 889925 (Mercury reference: 392-889925)\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eConfiguration:\u003c\/strong\u003e Individual coil-on-plug — one per cylinder\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eQuantity for Full V8 Set:\u003c\/strong\u003e 8 coils required\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eSystem:\u003c\/strong\u003e Cylinder-head ignition system\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eGTIN \/ UPC:\u003c\/strong\u003e 745061570443\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eCompatible Applications\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003eMerCruiser 496 MAG — serial 0M376088 and up (Design II)\u003c\/li\u003e\n\u003cli\u003eMerCruiser 496 MAG HO — serial 0M376088 and up (Design II)\u003c\/li\u003e\n\u003cli\u003eMerCruiser MIE 8.1L\u003c\/li\u003e\n\u003cli\u003eMerCruiser MIE 8.1L HO\u003c\/li\u003e\n\u003cli\u003eSelected MerCruiser 8.1L Inboard applications\u003c\/li\u003e\n\u003cli\u003eSelected MerCruiser 8.1L TowSport applications\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eImportant:\u003c\/strong\u003e 496 MAG engines through serial 0M376087 use a different Design I coil — confirm your engine serial number before ordering\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eSerial Number Fitment Notice\u003c\/h2\u003e\u003cp\u003eFor the 496 MAG family, the Design II coil (8M0178581) begins at serial number \u003cstrong\u003e0M376088\u003c\/strong\u003e. Engines through serial 0M376087 use a different Design I ignition coil and require a different part number. Always verify the serial number before ordering.\u003c\/p\u003e\u003ch2\u003eWhen to Replace\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003eEngine misfires on a specific cylinder confirmed by diagnosis\u003c\/li\u003e\n\u003cli\u003eRough running, hesitation, or loss of power traced to one cylinder\u003c\/li\u003e\n\u003cli\u003eDifficult starting associated with an ignition fault code\u003c\/li\u003e\n\u003cli\u003eCoil shows physical damage, cracking, or failed electrical connector\u003c\/li\u003e\n\u003cli\u003eCoil resistance or output is outside Mercury service specification on testing\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eInstallation Notes\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003eDisconnect battery power before beginning any ignition system service\u003c\/li\u003e\n\u003cli\u003eConfirm the affected cylinder through proper ignition-system diagnosis before replacing coils\u003c\/li\u003e\n\u003cli\u003eInspect the spark plug and plug connector on the affected cylinder while the coil is removed\u003c\/li\u003e\n\u003cli\u003eCheck the coil electrical connector and wiring harness for corrosion or damage\u003c\/li\u003e\n\u003cli\u003eSecure the replacement coil with two retaining screws per the Mercury service diagram for these V8 assemblies\u003c\/li\u003e\n\u003cli\u003eReconnect power and verify correct operation before returning to service\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eTechnical FAQ\u003c\/h2\u003e\u003cp\u003e\u003cstrong\u003eWhat is the difference between Design I and Design II coils on the 496 MAG?\u003c\/strong\u003e\u003cbr\u003eMercury updated the cylinder-head ignition system on the 496 MAG at serial number 0M376088. Engines at that serial and above use the Design II coil (8M0178581). Earlier engines through 0M376087 use a different Design I coil. The two designs are not interchangeable — always confirm the serial number first.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eHow many coils does a V8 application require?\u003c\/strong\u003e\u003cbr\u003eOne coil per cylinder. A full 8-cylinder engine requires 8 coils (8 x 8M0178581). If only one cylinder is misfiring, only that coil needs replacement — but it is good practice to inspect all coils for physical damage or corrosion during service.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhat did 8M0178581 replace?\u003c\/strong\u003e\u003cbr\u003e8M0178581 supersedes 889925 (Mercury reference 392-889925). If you have been ordering 889925 for a Design II application, 8M0178581 is the current OEM replacement.\u003c\/p\u003e\u003ch2\u003eParts Desk Insights\u003c\/h2\u003e\u003cp\u003eThe most common ordering mistake with this coil is not checking the 496 MAG serial number — Design I and Design II coils look similar but are not interchangeable, and ordering the wrong one is a very easy mistake to make on this engine family. When a customer reports a cylinder-specific misfire on a 496 MAG or 8.1L, this coil is the first replacement candidate after the spark plug has been ruled out. It’s also worth checking the plug connector and wiring at the same time, since corrosion at the coil connector is a common cause of repeat failures after a coil swap. Browse the full \u003ca href=\"\/collections\/mercruiser-marine-engine-parts\"\u003eMerCruiser Marine Engine Parts\u003c\/a\u003e collection for related ignition and engine components.\u003c\/p\u003e","brand":"MERC","offers":[{"title":"Default Title","offer_id":51324694396964,"sku":"8M0178581","price":336.59,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0743\/5799\/7604\/files\/5777d28d-41f0-4482-85e8-54dd458b0333.png?v=1788205315","url":"https:\/\/marisolmarine.com\/products\/mercury-mercruiser-ignition-coil-8m0178581-496-mag-8-1l","provider":"Marisol Marine Company","version":"1.0","type":"link"}