OK so ive got a 99 gsr, all stock exept for an apexi ws2 cat back. Since i put the cat back on ive been getting a CEL, but the car wasnt rite befor that, im only getting like 22 mpg and get alot of black stuff on the rear bumper, i think its running rich, ive done a cap and rotor and plugs, with no difference, I just wanna get it running good, i dont beat it real bad but i do drive it, but some friends of mine have integras and one ls civic, my car feels slower than another stock gsr i drove, and these guys get way better mileage while romping on their cars bigtime.... I need some ideas... thanks

 

Have you checked to see what the cel is for?
When i put on my axle back, a wire was somehow pulled out of my primary oxygen sensor and i didnt know it. I was getting crappy gas mileage, cel and black stuff on my back bumper too.

If the cel is for the oxygen sensor then check the wires first before ordering a new sensor.

 

when my buddy installed a header and exhaust on his 99 gsr, he was throwing a cel because of too much air flow or something weird. im not exactly sure or rememeber, but i remmeber he switched to a jdm ecu for another year and his problem went away. if someone can bridge what im saying, thad be cool.

 

thanks for the ideas the wires did pull out of my primary o2 sensor and i put them back in ... maybe they popped out again.... im going to try a new ecu too, and i will check what the cel is for... thanks again.. anything else???????