Thread: Running 2002 GTP w/o cat = bad MPG???

Hey there, This past summer the catalytic converter 1st stage fell apart and plugged the 2nd stage section on my 2002 GTP which prompted me in deleting the cat. Prior to the cat failure the car ran good with decent mileage (approx 25 mpg). Since then I have changed the plugs out for Autolite copper 606's side gapped to 0.050" as well as NGK oem replacement wires. Now under the same driving conditions of 50/50 highway & city I am only getting 17 mpg. My question is if I need to run an O2 emulator in order to improve the mileage. My scan tool shows that the Catalyst Efficiency code comes in repeatedly every 100 miles approximately. Anyone out there experience these symptoms?? Any feedback is much appreciated,

Thanks in advance, Jeremy

Originally Posted by bluegtp91

Jeremy...since your car is a '01+ car your only option is to leave the rear o2 and have the code set to no report...they '01+ cars NEED a rear o2 to run correctly.

I have a 2001 and I have no problems with my rear O2 removed.

The rear O2 issue is hit and miss on the 01+ cars. Most of the time it's easier to leave the rear sensor in, and set the code to not report, but leave the diagnostic code turned on so it will read the senor.

Ok, so my best option is just to disable the routine O2 sensor reference. How do I go about doing that? As far as driving style goes I rarely go WOT and use the s/c for the few hills along the highway between home and the city. Cruising at speeds of around 65-70 mph. Prior to the cat getting removed MPG's were substantially better even with wore out plugs and wires. The car only has 95,000 miles on it and I run 91 octane fuel. I just refilled the car and it worked out to 18.4 MPG. The onboard computer is saying that I am getting 19.6 MPG.

So if the code is set, that means it's reading the rear O2 like it should.

You might have problems someplace else.

Sometimes the vacuum leak is too small to find just by listening to the engine...say a pinhole, or a crack in a line boot won't always make the engine change rpm when you hit it with carb cleaner. The best and true way to tell is with some sort of scanner. The car's sensitive to the slightest changes, so even a leak you can't normally tell is there, you're likely to find by looking at the fuel trims on the scanner. It's so much easier that this is the first thing I do when I start tracing for leaks.