Shouldn't I be getting BETTER gas mileage with the catalytic converter removed?

Asked by Sep 14, 2016 at 08:36 PM about the 2004 Ford Escape XLT 4WD

Question type: Maintenance & Repair

Hello from New Zealand! I just bought a 2004 Ford Escape 3.0 V6 with ~70K miles on it. The catalytic converter had been professionally removed before I purchased it, and over the last 2 tanks I've been getting terrible gas mileage (around 14 mpg with 50/50 mixed driving). From what I've heard, removing the cat can (with appropriate tweeks) give you BETTER gas mileage and not worse. Also consider that in New Zealand they don't water down their gas with ethanol. So what gives?

I've had it hooked up at the mechanics and it's not running rich or kicking back any codes, at least according to the upper 02 sensor (which was left in place).

Now let me lastly say before I get the onslaught of colloquial fuel economy "wisdom", that I'm a hazmat commercial driver with over 100K miles on the road, so NO it's not driving habits, and YES I have run through the normal gambit of oil change, filter check, tire rotation/alignment, suspension etc etc.

I owned this exact vehicle in the U.S., and even with the cat on I would average 19MPGs driving like a maniac on terrible tires, bad oil and shot suspension. So I'm not going to be easily convinced that this is anything but a fuel system issue.

That being said, gas is $1.79 a liter here and I need better economy, ahh!

Thanks everybody!

P.S. It's not illegal to remove the cat in New Zealand.

5 Answers


I get 20mpg average on my Mazda Tribute, same as the Escape. Removing the cat reduces back pressure. But let me ask this, you said the upper O2 was in place, what about the lower? Do you have a CEL on?


The computer might be adding more fuel because the system is detecting a lean condition not enough to set off the CEL.

Hey Tom, not sure about the bottom 02 sensor, I THINK it's there, but not sure, definitely no check engine light however.


I was a go to guy for my old 4X4 club, so we kinds messed around with exhaust systems as most of those rigs were never driven on the roads and we found out the the later model engines actually got better mileage and performed better with the catalysts hooked up, from what I gathered that those engines need a slight amount of exhaust back pressure to make the system's respond properly, so some the rigs that were late model power plants ran catalytic converters and straight pipes from there. Don't know if this info will help there where you are but it was just something we found out with experimentation.

Thanks guys. I'm wondering if there's a way to get back pressure without having to re-attach a cat. Any ideas on that? I'm not as car literate as I"m pretending to be, so whatever you say here will be run by my mechanic.

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