Topic: Bad cat vs gas mileage question...

[TahoeYJ]

I recently had to have my Jeep smogged, and it took 3 tries for it to pass  the third time my buddy who owns the smog shop said to put some 31's on so it's run at a higher RPM during the test which was the only reason it passed (it was running high NOX numbers), and it barely passed with the 31's. He said the cat is more than likely bad, even though it's only like 2 years old...

It seems that over the past 6-8 months or more, my gas mileage has dropped at least 1.5-2 MPG. Is it possible, even though it's an OBD1 vehicle and there's no o2 sensor near the cat, could it still effect gas mileage? My rig runs great and never seems to miss a beat, but ever since my smog test I keep wondering if it could be effecting MPG's... Maybe my foot has just gotten heavier over time? 

[sharpxmen]

I recently had to have my Jeep smogged, and it took 3 tries for it to pass  the third time my buddy who owns the smog shop said to put some 31's on so it's run at a higher RPM during the test which was the only reason it passed (it was running high NOX numbers), and it barely passed with the 31's. He said the cat is more than likely bad, even though it's only like 2 years old...

It seems that over the past 6-8 months or more, my gas mileage has dropped at least 1.5-2 MPG. Is it possible, even though it's an OBD1 vehicle and there's no o2 sensor near the cat, could it still effect gas mileage? My rig runs great and never seems to miss a beat, but ever since my smog test I keep wondering if it could be effecting MPG's... Maybe my foot has just gotten heavier over time? 

it works harder to push out the exhaust gasses so yes, would affect your gas mileage - not sure by how much and if all the 2mpg is caused by it, but it will affect it and how much depends on how bad is plugged.

[chrisfranklin]

My second to last go around passing emissions, I finally passed after fixing an exhaust manifold bolt that had come loose. At least that seemed to be the problem.  http://4bangerjp.com/forums/index.php?topic=2421.0. 

[Jeffy]

Well, since you have a YJ, I highly recommend a MagaFlow cat.

The only time a cat should die prematurely is if it breaks up or if you running rich and it's getting into the cat and igniting.

The thing that sucks is that CA now requires a CA certified Cat which means you can't use any old aftermarket fat anymore.  Magaflow makes a 49 state cat for $90 and a CA cat for $199.

[TahoeYJ]

Well, since you have a YJ, I highly recommend a MagaFlow cat.

The only time a cat should die prematurely is if it breaks up or if you running rich and it's getting into the cat and igniting.

The thing that sucks is that CA now requires a CA certified Cat which means you can't use any old aftermarket fat anymore.  Magaflow makes a 49 state cat for $90 and a CA cat for $199.

That's what there, the guy I go to uses strictly Magnaflow/Carsound cats. I need to take a temp gun and check the temps going in and out, it's supposed to be hotter coming out if it's good, right? Either way, it looks like I'll end up replacing it in the near future

[Jeffy]

MagnaFlows are nice since they are bolt-on.  IIRC, yes, the temps are supposed to be hotter.