BambiB
Junior Member
My catalytic converter clogged, so I gutted it (cut the side out, smashed up the honeycomb, pulled all the pieces out, welded it shut). The truck runs pretty well, but now I'm getting 6mpg. I used to get 10mpg with the cracked cat. (I didn't know the rattle was a broken cat, so drove it that way for a long time before one day I hit a hard bump, the cat clogged and the engine wouldn't run.)
I had read that the upstream sensor may go bad with a bad cat, so I replaced it. No "check engine" light. No OBD codes. Just 6mpg.
Some (in a much less knowledgeable forum) have suggested that the cat's back pressure is vital to engine performance/mileage, but other posts I've read here seem to suggest that it really makes little difference - and in fact should slightly improve performance. Performance DOES seem to be improved (acceleration) - but then, I don't know how long the cat has been a problem, so it may not be a fair comparison.
One other relevant factor: I changed tires just before the cat clogged. The truck had oversized tires when I got it (not monster truck size, but just big enough that when you cranked the steering wheel they'd rub the frame), and I replaced them with a recommended size. Since mileage is recorded as a function of the number of revolutions, I would not have been surprised to see mileage appear to increase with smaller tires. I have not yet done a GPS/measured course versus odometer comparison, but I would expect it to show I'm actually getting less than 6mpg.
Do you Dodge Detectives have any suggestions where the extra 4mpg went?
Thanks in advance for your saged advice!
I had read that the upstream sensor may go bad with a bad cat, so I replaced it. No "check engine" light. No OBD codes. Just 6mpg.
Some (in a much less knowledgeable forum) have suggested that the cat's back pressure is vital to engine performance/mileage, but other posts I've read here seem to suggest that it really makes little difference - and in fact should slightly improve performance. Performance DOES seem to be improved (acceleration) - but then, I don't know how long the cat has been a problem, so it may not be a fair comparison.
One other relevant factor: I changed tires just before the cat clogged. The truck had oversized tires when I got it (not monster truck size, but just big enough that when you cranked the steering wheel they'd rub the frame), and I replaced them with a recommended size. Since mileage is recorded as a function of the number of revolutions, I would not have been surprised to see mileage appear to increase with smaller tires. I have not yet done a GPS/measured course versus odometer comparison, but I would expect it to show I'm actually getting less than 6mpg.
Do you Dodge Detectives have any suggestions where the extra 4mpg went?
Thanks in advance for your saged advice!
