Oxygen sensor locations?

[376shovel]

I thought there were 2 o2 sensors but apparently there are 4? Where are all 4 located? I know only of the two between the cats and pre cats. Are the others in the stock manifolds?

[fastblackmerc]

I thought there were 2 o2 sensors but apparently there are 4? Where are all 4 located? I know only of the two between the cats and pre cats. Are the others in the stock manifolds?

On a stock MM there are 2 upstream (before the cats) and 2 downstream (after the cats). As far as I know the MM has no "pre-cats".

[376shovel]

Any pics or specific locations?

[fastblackmerc]

Any pics or specific locations?

Get under your MM and look. They are very hard to miss..........

[376shovel]

Disregard, I found an image on rock auto

[376shovel]

I would but its buried in snow and I'm laid up with an injury

[fastblackmerc]

Why would you need a picture? You either need the upstream one(s), the downstream one(s) or both.


BTW... if you are replacing one side , do both sides.

[376shovel]

It's for planning performance type exhaust

[fastblackmerc]

It's for planning performance type exhaust

Performance exhaust:

Remove all four cats

Remove downstream O2 sensors

Install Two hi-flo cats

Turn off monitoring the downstream sensors in your tune

[376shovel]

I was looking into doing exactly what's in this article
http://www.mustangandfords.com/how-to/engine/mdmp-0904-2003-mercury-marauder-exhaust-install/photo-gallery/#15

[RubberCtyRauder]

^^^what FBM said, and if adding longtube headers, will need tune as well since upstream sensors are further away they need to have a delay put in the tune or something like that or will get code

[376shovel]

What's the advantage of removing the rear o2 sensors? And will it pass inspection

[Logizyme]

On a stock MM there are 2 upstream (before the cats) and 2 downstream (after the cats). As far as I know the MM has no "pre-cats".

The forward catalysts are actually "pre-cats"

[fastblackmerc]

The forward catalysts are actually "pre-cats"

Good to know :up: