Technical question looking for an answer

SVX10 · #1 11-20-2002, 10:14 AM

Technical Q&A baby! Anyway, I was wondering if the catalytic converters have any effect on gas mileage. I'm asking because my gas milage has dropped, and I don't know why. I'm thinking of things i've done lately that could cause a drop, and I thought maybe removing the two front cats could have an effect. Optimally, I would've noticed a gas mileage drop right after cutting the cats, but, unfortunately, in the few months after the cats were cut, I was doing short 2-3 mile trips maybe 2X/ week...not the best setup for measuring fuel efficiency. I've noticed that some newer cars have cats that contribute to the rich/lean reading of the O2 sensors somehow. Is there any way I can test my O2 sensors to see if they're bad? I'd really like to get my mileage back up since I drive 60+ miles daily. Thanks.

Mat

#2 11-23-2002, 10:37 AM

I have two thoughts:

1) if an O2 senor was bad, your check engine light would go on (assuming that the light works...check its operation during the "self test" when you start your car)

2) Some back-pressure in the exhaust system is GOOD. It actually helps the engine perform better by something called the "scavenge effect"....ask Beav to explain it to you. Anyway it also helps with gas mileage. Yes, in some cars that have too much back pressure releasing some of it could help the cars performance...but by cutting out the cats you probably lowered the already low pressure exhaust system of the SVX to the point where there isn't enough pressure to operate properly. Case in point: my younger brother recently took the front pipe off of his 90 Legacy to see if it would go faster without any exhaust. Well it did make the car A LOT louder (it actually sounded cool) but it was SLOW AS HELL. Why? Without a certain amount of back-pressure the engine couldn't perform correctly. It also ate through gas like it was going out of style.

Hope this helps

Dave