Can someone tell me the difference between these two engines? I'm trying to find an O2 sensor for my 2009 F150 and while looking for parts I came across this (apparently) very important distinction (note the "W" vs. the "8" at the end). I've looked on VIN # decoders but they stopped short of this information.

Thank you very much for your time.

BTW I'm not a mechanic so feel free to elaborate if you can.

  • 4.6L v8 sohc distributorless naturally aspirated SFI electronic fi MFI 8


  • 4.6L v8 sohc distributorless naturally aspirated SFI electronic fi MFI W
  • Welcome to Motor Vehicle Maintenance & Repair! Which O2 sensors are you looking for? The upstream (pre-cats), downstream (post-cats), or both? – Pᴀᴜʟsᴛᴇʀ2 Dec 31 '17 at 17:17

To differentiate, you're looking for the 8th digit in the VIN. Here's how it aligns:

  • "W" is a 4.6L 2v
  • "8" is a 4.6L 3v

The "2v" or "3v" denotes the quantity of valves per cylinder. It should more than likely say on the top of your engine whether it's a 2v or 3v engine (on the plastic bits).

As for the O2s themselves, it appears there are separate O2 sensors for left/right pre-cat and left/right post-cat, meaning, you could be looking at four different part numbers to replace all four of your sensors.

  • As a quick visual, 2v engine valve covers have a straight edge on both sides of the cover. The 3v valve cover has a straight edge on one side and a scalloped edge on the other. – mikes Dec 31 '17 at 19:16

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