Raise

iTrader: (31)

im throwing a p0420 code and i think its my drivers side cat goin bad. i noticed that im only getting around 225 miles to a tank and my car is a 6-speed with stock motor and exhaust. this sounds a bit low to me. i was just wondering if that might be the reason....???

One Kool Cat

iTrader: (1)

yes a bad cat will definately eat up gas mileage, and power too!

Raise

iTrader: (31)

how so??

2001NBMZ28

Think you meant P0420. <80k? Get GM to replace it free.

98RedBird

iTrader: (77)

because the motor is working that much harder to get the exhaust gases out.. it's kind of like trying to blow through a straw that is all clogged up with something... it doesnt work too well

One Kool Cat

iTrader: (1)

What was the description of p0420 ?
depending on what the 02 sensors are reading, it may think the car is running lean (not enough fuel) and therefore richen (more fuel) the fuel mixture, causing more fuel to be dumped when its really not needed.
So the computer is asking for more fuel when the engine doesnt need it, that results in more unburned fuel to pass through, more fuel= less gas mileage. and poor performance under these circumstances

2001NBMZ28

P0420 is Catalyst System Efficiency Below Threshold Bank 1, it's a post cat 02 code.

Raise

iTrader: (31)

yeah it is p0420. i was wondering if it was a bad cat or o2 sensor. as far as replacing the cat, im about to do headers/ory so i dont really care about the cat. but i was just wondering if my bad gas mileage was attributed to the cat or if there was something else going on with the car. i dont wanna dive in and start moddin if the car had an issue i dont know about.

blue02formula

iTrader: (1)

I guess it could, but I'm throwing the same code and I got 23mpg last tank. I've been trying to keep my shift points @2K since 93 oct. went to $3 a gallon here. When I get a little heavy footed I was getting about 20mpg, but I also have 4.11's.

RevGTO

iTrader: (12)

I had that code after lugging around town with an elderly passenger in my car. I ran a can of fuel injector cleaner through it on my next tank of gas (BG 44K), had the code deleted and it has not returned.

Raise

iTrader: (31)

well, the weirdest thing happened. the ses light is off now. its been on for over a week now, and all of a sudden, its gone. im sure the problem is still there, but thats weird how the light just went off. anyway, headers/ory are on the way, but i thought i would ask to see if the cat/o2 issue is what has been causing my gas mileage drop.