running rich / low mpg

[steagle]

i've posted about this before and i know there are several threads on the subject but i wanted to see if i can really pinpoint my issue after observing the car for a couple more weeks. i am still averaging 13mpg around town and even on the highway, after a mpg reset on the pcm i max at around 16mpg. i know my 20"s arent helping the situation but come on i should still be getting better than that. i only fill up with mobil or shell premium gasoline and dont need an oil change for another 2k. one thing i noticed is when idling, there is a higher than usual amount of exhaust coming out of my pipes. i'm assuming i'm running a bit rich as the exhaust is clearly visible even with no moisture in the air.

i cant bring the car in for another couple weeks because of travel circumstances, so it's going to be used sparingly in the meantime, but i want to get an idea of the major things to check for - fuel filter? air filter? 02s? cats? what have you guys done to fix this? thanks for the input.

 

[TheRebel]

For the money, I'd try an air filter. Cheap step and won't hurt to change it anyways

 

[5.7sbc]

I'd check the o2 sensors, if they are malfunctioning your computer may be pushing too much fuel through the injectors. I have not had the problem you descibed w/ my LS but I have had that problem on other vehicles and the o2's were the problem.

 

[steagle]

02's were my first guess too, since i pulled an error code at autozone recently that referenced the bank 1 sensor running below threshold or something to that effect. 02's are about $120 a pop right?

 

[5.7sbc]

OEM are probably around that price and I would go with those. Aftermarkets tend to have a wider band for what is considered proper opperating temp. this can cause problems. You basically get what you pay for with o2's.

 

[2001LS8Sport]

First things first....replace your fuel filter if you haven't done it in a year or so. I don't know why it is, but I have seen mileage actually improve by doing so. You would think a dirty filter would make it run lean and give you better mileage, but I've actually witnessed a mileage improvement many times.

Next, don't use the mileage calculator on your car. With your oversized tires, it's not accurate. And if you haven't recalibrated the speedo, I don't know how you can get any type of accurate reading without driving a known distance and refilling your tank and calculate. Of course, if your 20's are the same height as the stockers, this whole paragraph is moot......