Hi, I recently removed the Cat on My 00,5.9,R/T, due to the fact that it was shot out & doing nothing but rattling,making noise. I had a shop replace it with a length of straight pipe until I can save up enough money to replace the Cat. Which I'm hearing $ 1000 +. It seems to run Ok like this but it sucks up the gas like it's the latest sport. Any ideas what I might try to back it off the fuel just a little bit? Thanks in advance for reading My post & any ideas that You may have.

 

You can get an aftermarket cat for a LOT less than the cost of an OEM unit. Magnaflow makes some good, direct replacement cats. Might wanna have a look at 'em.

What kind of gas mileage are you getting? I am thinkin' if you are in the neighborhood of 14-15, that's about as good as the 5.9 is going to get. If it's worse than that, might consider having a look at tune-up parts, and possibly the front O2 sensor......

 

Hey You, Thanks. Im getting around 12 mpg. So come payday I get a few tune up treats & see if I can dial it in a little better. Great advice. Living here in CA bay area where Our gas prices are the highest in the Nation premium being $ 5.40 a gal, which is all I run in My truck any improvements at all will help out some. A few weeks back I attempted to order a much discounted Magnaflow Cat & beings I live in CA They refused & by law said They could not sell it to Me. I have about a year before I will have to take it in for a smog check in order to renew My registration so until I am able to come up with the money to buy a CA legal Cat... It is parked for the most part .

 

Doesn't magnaflow have some cats with CARB EO numbers??? I thought they did..... Or does california require OEM cats? (wouldn't surprise me..... )

If there is over 100K miles on it, change the front O2 sensors as well. NTK or Denso sensors only please.

 

I think your poor fuel mileage is due to the missing cat. The O2 sensors are going crazy and not suprised that your rig is not throwing a code due to missing cat. If you are getting 12mpg overall, you are doing good. My 00 R/T is varying between 10-12 mpg driving around town. 12-14 on hwy. the 5.9's are thirsty. Especially the R/T due to its 3:92 gear ratio also.

Fortunately Texas fuel is not as expensive as compared to other states. Paying just under $4 for premium fuel that my R/T requires.

 

Only the upstream o2 sensor affects the mixture. The post cat sensors only tattle on the converter not doing it's job.

 

My 98 Durango SLT plus is 4x4 5.9 engine. I have stock cats and magnaflow mufffler, 179K on the clock. Get 13-14 in town and 20mpg on hwy. Still runs and looks almost like new. Guess I'm lucky it gets such good mileage.

 

Yes, Mangaflow carries CARB and EPA converters.

I had my Converter replaced around 2017 when I decided to have my exhaust upgraded to a high flow cat back dual exhaust. I cannot remember the brand of cat they got me, I think it was a magnaflow. It's a very high flow low restriction converter while maintaining emissions restrictions for Texas. I definitely feel the 5.9 breathing much easier at the mid range to upper end with the new high flow cat and dual exhaust using one in and two out FloPro muffler. 3 inch exhaust from cat to muffler. then 2.25 inch for the dual exhaust exiting out the FloPro.