I have been running my car for a while now with no cat and with reduced fuel mileage. What would be my best options to get the car to stop dumping so much fuel as it is compensating for not cat? Would my only option be a tune, or do I have other options? Thanks!

 

Don't worry ^ I'm in the same boat. And as far as I know putting a cat in or Getting a tune are the only options. How much down on MPG are you?

 

When I first got the car I was getting about 30-32mpg depending on how I drove, I am only getting as high as about 27 now

 

Dang, Ive never actually calculated my mpgs since i installed my catless I just know it was down...I need to do that to see what Im getting.

 

Are you guys throwing a code for the catless downpipe? If so, that explains why it's running rich all of the sudden. Either throw a defouler on your O2 sensor so it doesn't trip the CEL again, or get a tune.

 

Car dumps in extra fuel in only on warmup or when cat overtemp is calculated by the ECM. Whether or not you have cats the effect is the same and the fuel mileage should be the same if your driving style is the same. Removing cats effects VE of the engine to a small extent but not enough to where reduced or increased fuel economy is normally seen. The LSJs though have only narrowband O2 sensors and are not in constant closed loop though so that causes the car not to be able to compensate as well as it could for the fueling need changes you see which could account for the reduction in fuel mileage.

 

Mine doesn't read rich, but it sure smells it. Probably the small deflections the ECU is making to kick extra fuel to the cat is.

Getting a tune should fix your rich issue. You'll get better fuel mileage as well.

 

Yes, I have a defouler so that I don't throw codes. Like YellowEye stated above, I can smell that my car is running rich, and I can see the difference in my fuel mileage.

 

You are smelling the nitric oxide and other noxious gases the cats break down. If you are smelling raw fuel in the exhaust you have other issues.

 

I changed my plugs to NGK one-step colder brand new, back to getting around 33 interstate again