I use to get around 15mpg around town until I did some mods. After I installed LT headers, 160* thermostat, new plugs/wires, and MadZ28 tune I've gotten about 10-11mpg. I babied it big time this whole week and I got only 13mpg. What is the problem??? BTW: the MadZ28 tune boosted my idle from stock to 900rpm if that makes any difference.

 

anyone???

 

That's odd. How many miles? Have you ever done plugs/wires/opti/coil/icm/o2 sensors? Have you scanned the computer for any codes? Codes can set without an SES light on.

I only get 15 in town when I really granny it. Gets a cool 27+ on the highway though

 

68,000 miles with brand new plugs and wires. Original opti, 02 sensors and such but the car drives 100% fine it just gets terrible gas mileage. I got 15 mpg before I did the LT Headers and tuning. I ran open headers for only like 10 miles but maybe the 02's are fried???

 

replace your o2s and dont get bosch o2s go with acdelco. i kept blowing bosch o2s so i just replaced them with acdelco and got like 30 more miles to a tank.

 

Yeah I second the o2 sensors. Had the exact same problem on my truck, bad mileage with no symptoms and that's what did the trick