At what point in mileage do we change our cats? I've read it's prudent every 100K in some forums for Chevy's. I've got over 226K on my Dak and am sure they've never been changed and my mpg's have dropped 4-6 in the past 50K or so.

No codes, just a curious question.

 

I am no expert but I would say don't replace the cat(s) unless you get a code for a cat problem. I had to replace my own cat and y-pipe assembly back in November but I had a code P0432 for cat effeciency below specs. Now the O2's are a different story. They do get slow and lazy with age and will cause lower mpg. I have read it is best to change the upstream O2 sensors at 75 or 80,000 miles. I did both of my upstream O2's and MAP sensor at about 80,000 miles and it definitely improved power on the butt dyno and mpg went up a few as well.

Jimmy

 

Did them last year. Just did my annual cleaning of the TB last week and saw an increase back up to 18 mpg hwy. Not that a cat is a cheap fix for low mpg, but I'm askin'.

Best I ever saw was when my fuel pump needed replaced. Got damn hear 21 mpg... don't think I'll ever see that again.

Thank you1

 

The precats are monitored for efficiency, the main cat isn't.

You can check for an exhaust restriction, such as a plugged cat, with a vacuum gauge. I wouldn't replace it unless necessary either.

 

Well I'm on the fence regarding this one

I say replace it that's a lot of miles its going to have some restrictions inside it.

Unless you plan on selling the Dakota then I wouldn't do it

I jumped the gun with my all new exhaust system I had it replace with everything at the same time my exhaust should last another 10 years.

 

A lot of good input! I love the truck too much to get rid of it (any time soon); I'll probably keep it until it dies.

I wonder what would happen if I just removed the second cat... There are no sensors monitoring it.

 

It shouldn't do anything if you remove it. Around here though I'd get bagged on the visual inspection (emissions).

It doesn't have to work, just be present. All they do is check for codes.

 

They do run a mirror under the truck, must be that's what they're looking for.

 

To fix my mpg all I did was get new sensors for transmission
545rfe has 2 speed sensors that act up and never gives trouble codes. The first sensor toward engine does the shifting overdrive etc and the second one toward the back does the speed