Improving Fuel Efficiency

sell car... buy compact 4 cyl... win

bbayne95...are you talking mods like UDPs, CAIs, exhaust, etc...that are capable of improving gas mileage? Other than that and basic maintenance there isn't really anything you can do...however if the problem has gotten worse over the years then I'd bet money that there is some issue you haven't addressed. Maybe your tires are bad, maybe the air pressure is too low, maybe you're out of alignment, maybe there's a body in the trunk that you forgot all about (hahaha!!)...there's really nothing else you can do.

Worn rings and valve seals will also contribute to a loss in efficiency and performance

You named the big items which you need to keep up on maintenance. Plugs, O2 sensors, filters, change the fluids.

My GT has 196k miles and it still seems to do well on gas. A recent trip to Colorado, I got 27+mpg while in the mountains. On the drive there and back, it got the usual 24-25mpg at 80mph.

I changed my O2 sensors when the car had something like 150k miles. I remember it made a nice difference. Old O2 sensors can be slow to cycle, and thus don't do as good of a job keeping the desired AF.

Personally, I've never seen a reason to clean injectors unless there is actually a problem. The snake oils which supposedly clean your fuel system are just that.

A few comments:
Tire selection can make a big difference on gas mileage. Most performance tires have large tread blocks, and are designed for traction.. thus rolling resistance suffers. There are some performance tires that do ok on gas, but you more or less get one or the other.
Bald tires actaully have less rolling resistance than new tires. New tires will have deeper tread, and loose more energy due to treat squirm (deformation of the tread). Bald tires are also slightly shorter and will indicate more miles traveled than new tires, thus increasing your calculated mileage.

Synthetic fluids can help increase mileage, along with ligher weight oil. If your engine hasn't been getting synthetics, it probably isn't a good idea to change now. I still run full synthetics at my mileage.

The O2 sensors if never changed will make a difference.

bbayne35...which tune are you using on the Predator. I use Sniper and I de-tuned my car to run regular gas for a few weeks back when gas prices were really high. I noticed increased fuel efficieny and I paid less for the gas. But I also noticed how much performance I lost. It's give and take...what's more important. Maybe you should de-tune your car and see how it responds.

You say you've "modified the car with bolt-ons over the years (exhaust, udp, throttle body, intake plenum, Predator tune)" and have noticed that "fuel efficiency has diminished over the years".

This is probably not a coincidence. You like the sound of the exhaust, appreciate the extra oomph on the on-ramp etc and have been -- perhaps unconsciously -- dipping into the throttle more because of that.

Having said that, O2 sensors should be considered a wear item and replaced before the MIL indicates a problem for peak efficiency. 60K miles is a typical replacement interval. If you've dumped octane booster into the tank because of, say, an aggressive timing curve from the tuner the O2 sensors may have been contaminated and become less effective.

You might want to verify there's no drag being introduced by a sticking caliper or parking brake cable, especially if the car sees winter roads, slush and salt.

Aside from the obvious maintenance stuff, the best way to achieve good mileage is to place a proverbial egg under the gas pedal. None of your bolt-ons should prevent a return to decent fuel economy if you keep your foot out of it.

Don't feel bad: With my KB I get about 200 miles between fill-ups with spirited, mostly-city driving...

I'm still knocking down 18mpg in my Vortech GT. I have an ORX and Magnapacks, 3.73's and I still get on it a couple times a week. It is my daily driver. I change plugs annually. I also change my oil every 3k miles if not slightly early. I run a aluminum driveshaft and have a couple weight savings mods.

I think my mileage is partly in the tune, partly in the tires/weight savings/maintenance and partly in your driving habits.

Remember mileage starts with rolling resistance, as mentioned earlier, traction oriented tires will hurt rolling resistance, as will dragging brakes. A lighter wheel will increase mileage and performance. A harder compound tire will help too. Running coilovers and a tubular k member will as well.

When driving avoiding super short trips and long idling times will reduce mileage by up to 20% in any car. If a manual try getting to top gear as quickly as possible. Avoid engine braking. Avoid hard stops, hard launches. Coast to a stop if a manual. Draft when possible (safely)

Couple quick things to help without even starting the car, re tune it and make sure your tire pressures are correct. And next tank keep my driving habit ideas in mind.

how the hell did you get 27mpg??? i have a 2002 gt with cai, lts, o/r h, short shifter, stage 1 clutch, alluminum d/s, 24lb injs, new plugs, new o2s, valvoline synthetics, and usually get about 18-19mpg, 21 when i dont haul ass. i also think i have a small vacuum leak or exhaust leak somewhere. im pretty sure i dont need the 24lbs but they were on the car when i bought it.

Maintenance and a good tune are going to go a long way. Learning how to drive efficiently will make a huge difference as well. I can get 20-22mpg out of my GT with a supercharger, 3.73's, and 3900 stall torque converter.

cruise control on the highway is what helps me knock down 21mpg. but that is with that vacuum problem. i think the pcv valve hose to my plenum is being sucked shut. anyone know if that would cause idle problems, worse gas mileage, and p1131 and p1151 cels?