O2 sensor washer hack

l008com

Original poster
Member
Feb 19, 2016
886
Massachusetts
My exhaust O2 sensor is causing check engine lights, indicating my CAT(s) are not working as well as they did back when the truck was new. Unfortunately I can't afford to replace them right now, and I can't get an inspection sticker with a check engine light on. Thus, I'm thinking about this washer hack. Apparently you put a washer in before you screw in the sensor and it senses less.

Has anyone done this before? How easy is it? How thick a washer (or stack) do you need? My local hardware store has a great selection of stainless steel washers, will my truck run with one of hte sensors completely removed so I can bring it in and see what fits best?
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
It's actually done with spark plug defoulers. Unless they check under the truck, they won't know they're there.


Just be sure that the cats aren't plugged up with a backpressure test as that would cause other issues like loss of power and MPG.

Edit: Correction, you need the 18mm. Couldn't find the defouler but there is an actual O2 spacer.

 

l008com

Original poster
Member
Feb 19, 2016
886
Massachusetts
Wow those are a lot less subtle than I was expecting. I thought it was literally a washer or two.

Also how is a back-pressure test done? I assume it's not something I can do myself.

Lastly and slightly off topic, you can get a new dual cat exhaust piece on rock auto for about $400. It looks like it's a bolt-on piece. But is it really that easy? Is this someone you could do in your driveway with minimal mechanic experience?

The exhaust from my truck is starting to have the smell of an old vehicle. Granted, it is kind of old as a 2008 with 140,000 miles. I'm very much on the fence about trying to get rid of it asap, keeping it for a while, or keeping it for a long time, until it's dead.
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
Wow those are a lot less subtle than I was expecting. I thought it was literally a washer or two.

The idea is to take the sensor out of the exhaust stream so it only gets a whiff of it on a steady basis. Did it on my son's car years ago instead of spending $1000 on anew cat. Worked a treat. Inspections here at the time were just "plug, check and go", no visual inspection.

Also how is a back-pressure test done? I assume it's not something I can do myself.

Certainly with the proper equipment. Remove an upstream O2 sensor, use a low pressure gauge like a vacuum gauge connected to a fitting that can screw into the bung (compression tester fittings would work) or use a proper backpressure tester, start the engine. Shouldn't be more than 1-2 psi at 3000rpm.


Alternatively, you could also use a vacuum gauge on vacuum.


Lastly and slightly off topic, you can get a new dual cat exhaust piece on rock auto for about $400. It looks like it's a bolt-on piece. But is it really that easy? Is this someone you could do in your driveway with minimal mechanic experience?

It's exhaust work. Rusted or seized nuts, bolts and studs are the norm, may require torches and even removal of the manifolds, which runs the risk of broken bolts. I hate exhaust work. I'd rather pay someone to do it.
 

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