I just recently put in a K&N CAI, and a Magnaflow 18" one-in/dual-out exhaust in my 2003 Quad Cab 4x4 4.7 SLT.
Since doing it, I've ran two full tanks of gas and the rusults are scary!!! The first tank basically got the same gas mileage as stock (12 miles less). But the second tank ended up2 mpg less than normal (48 total).

As I've said in other posts,I'm not lead-footing it. In fact, I"m actually babying it a little. It just recently had a 36,000 mile tune-up, and brand new Champion plugsput in. But this was all done before the upgrades, so I don't understand.

Does anyone have any idea what's going on here? Will using a Superchip tuner help? I currently run Regular Unleaded, but would definitely be willing to step-up if it would help. Is this something a bad O2 Sensor would cause? HELP...HELP...HELP

Any input would be greatly appreciated...thanks!

 

with a bad O2 sensor you will get bad gas mileage. when my O2 sensor crapped out just before I put her away I was only getting 15mpg, and this summer I was getting 20-21mpg. so when I replace my O2 sensors then I should get my milage back.

 

I did the self test tonight, and no CODES came up. Is there still a posibility that the O2 Sensor could be bad?

Are there any other possibilities???

 

I doubt that there is anything wrong with your truck. If you getting 2 MPG less its probably how and where your driving, how many stops you take and how fast you go. i wouldnt worry about it.

 

If you have a bad 02 sensor then when you get on the gas real hard black smoke will come out of your exhaust. Just make sure that you check both of them, upstream and down stream sensors.

 

I never got any codes for mine. until it got soo bad that it would idle. but yes you will notice black smoke and it will be running rich.

yu O2 sensor will be just be giving a "false" reading and dumping more fuel into it. you can try and take them out and clean them. thats what I did and it helped out a lil bit. but I'm just savng up for new ones. $150 each[:@]

 

i just checked, kragen has the OE type bosch sensors for $66. you could replace them both for probably $130

 

and thats why I hate canada.

I should just but some online from the states

 

yeah. www.partsamerica.com www.napaonline.com or similar. I got mine from NAPA for 90ish. In the future I'll go with a generic one and splice the wires.