I tried searching for bad gas mileage issues but didn't really have much luck. Here's the situation I'm in and maybe you guys can help me out.

I've had my car for about 9 months, since I can remember the car has suffered quite a bit compared to other LT1 friends of mine when it comes to gas mileage. I get an average of 180 miles a tank with just around town driving, getting as good as 200 miles per gallon with about half of it being on the highway. I was wondering what things I should check to help figure out this problem.

I've changed the O2's last week, went through a tank since then and the mileage has not changed. The car is basically stock, but has a moroso CAI, hooker muffler, tb bypass. The car has no cat, but does have a bullet muffler in it's place. The fuel filter was changed about 6K miles ago. The wires are fairly new, the plugs probably could use a change but the car doesn't sputter or act weird at all. I raced a friend of mine in a 13.4 E.T. LT1 car and he barely pulled me because of 4.10s vs. my 3.42s. My car has ran a best of 13.62 in the past so I don't think it's too far off from that even with the poor mileage. The car runs pretty good but smells a little rich at idle, not that bad though. I'm going to try and get the car scanned, but the SES light is not coming on so that may not help.

Anybody have any idea what I might check out?

 

Well... have you taken any long trips recently? I get around 12 in the city, but on the highway i get about 18. I am also not stock at all. It mostly depends on how much you get on it.

I also picked up about 2 mpg when i went with the delteq ignition. Just a thought.

 

With the mods in my sig, my car gets about 210 miles per tank. Averages about 13.5-14.5 MPG, all in town and I get on it often. Haven't had it on the highway for any amount of time, so I don't know what it will do on the Highway.

 

I get about 15 around town. When I bought my car a few months ago, I got 25 on the road. With my mods, I got 28.9 on a trip to Denver last month.

 

that sound about right my milage is the same but I have the ltcc and a exhaust leak so that about evens things out I guess.
-b

 

Yeah that is about right. My car also came out around 180-200 in town. She's a stock with 110000 in it. But now she get a new 383 with some mods., and let see. I don't think these cars ever goes over 200 in town, except with a 80 years old driver..

 

Back before I blew up my 700R4 with 2.73s my car with the mods in the sig minus the 3.73s and t56 of course got 19 normal driving in town and 24 on the highway, but I have gotten as bad as 9 but that was WOT all the time

Taylor

 

i'd have to concur with everyone else. sounds about normal. or at least with my car. ive got a 97 TA with m6. no cats, bullets, tb bypass (like this makes a difference in mpg), a moroso CAI, and changed my o2's about 3 months ago. still got fairly new plugs and wires. i'm using 3.42's and get about 200-210mpg. at most. hope this helps.

 

well originally i had my formula running about 160-180 miles per tank aka 11-12 miles to the gallon (a/c on or off highway and city t-tops on or off didnt change anything)... but did plenty of tune ups to it, and got it up to 250 a tank 50%city/50%highway, aka 17 mile to the gallon... at 100% highway i got 350 to a tank aka 24 mile to the gallon.

check ur spark plugs... the wires, the intake, the fuel filter, air filter, catalatic converter... mine was the wires & cat (was running on 7 cylinders and had a backed up exhaust)... after i fixed those my car went gradually from 12-18 mpg and now its starting to go back down cause im running with a few bad wires

 

intake and exhaust would help, a little
the performance benefit was enough to convince me to do them

 

Well thanks guys, I think I'm going to check out the plugs/wires because I think they're a little on the old side. The previous owner of the car was spraying a 100 shot on the car so the plugs may be shot (runs pretty dang hard and doesnt miss at all- if theyre fouled i'd be surprised) there's also taylor wires on it. The fuel filter is fairly new, and there's no cat to be clogged. I'm also going to check out the CAI element, it's a moroso setup. Also check out the tb and intake and see if there's any big dirt accumulations anywhere. 13 mpg just sucks though, I usually hear 16-18 is common for city driving...I mean lately I haven't been ripping it and I still get the same mileage.

 

I checked my mpg about a month ago and ended up getting 13.8. That was with careful driving and very little to no hard pedal pushing. I checked it again with my next tank and got 16 mpg... but that was with quite a deal of WOT(my Tazzo arrived). Kind of wierd that my mpg went up the harder I drove the car.

 

I get about the same with my 94 formula. I think my record has been around 14 with about a 80/20 mix of city to highway driving. And my mileage doesn't get much worse when I get on it everywhere I go. I have replaced all the above mentioned parts, as well as many others in an attempt to "fix" this problem. No change.

I hit a point where I just don't care anymore. And since the loss of mileage between pokey driving and spirited driving is so minimal, you can guess how I drive.