I have a 93 Tracker, Dough Thorley header, 2.25" exhaust, Auto tranny, high-flow cat, K&N cone filter, and cherry bomb muffler.  I get about 15-18 mpg on the highway and 14-16mpg in town.  It's got plenty of power, acceleration is great, timing is right on 11* BTDC.  Tire pressure may be a little low right now, and the tires are just slightly bigger than stock (Maybe one size larger).  Why is my gas mileage pretty much crap?  My dad's 95 sidekick, 5-speed with slightly smaller tires get 31-33mpg highway, and 28-30 in town (Now that his timing is back in spec).

I've replaced my O2 sensor, and even tried running Acetone in my gas at 3oz/10 gallons.  Saw a decent improvement with the acetone...  Got me up to 19mpg highway, 17 in town.  Standard Regular unleaded gas here in Texas is rated either 86 or 87 octane.  I try to always got to stations that sell 87.

Highway RPS sit around 4000-4500 at 70 mph.  I've counted the shifts from a dead stop and the transmission only appears to shift 4 times instead of 5, so maybe my overdrive isn't working?  The only other very minor problem is that every so often when taking off from a dead stop there is short burst of normal acceleration followed by about a second and a half of almost 0 power where the tach drops way down and the engine sounds like it stopped, then it comes back to life and resumes normal acceleration.  Doesn't do that all the time, but it seems to have become more frequent the last few months.

I probably ought to clean my EGR and adjust my valves too.  Have everything I need to do that except time.

Is there anything else I can do to help improve my mileage?

first off on the trans, you start off in first gear, so add four that makes five with the t.c. loc up, on mpg try using a gps and air up your tires, you may be going more miles than you think, do you have a 16 valve or an eight valve engine?

It's an 8V engine.  Also, looks to be running a little rich as the tip of my tailpipe is coated with black soot.

I've calculated the mileage based on trips of known length, like the trip from my house to my grandma's.  I've made that trip hundreds of times over the years in various vehicles, and know the mileage exactly.  The in-town mileage rating is probably more apt to be off, but again I use a conversion factor based on the difference in odo mileage and known mileage for the longer trips to calculate city mileage.

IF it's an auto trans, it's a 3 speed with torque converter lockup. It will drop aprox 500 rpms when tcc engages. 11 degrees btdc doedn't sound right, should be more like 8. Also try airing up your tires.

I honestly think it's partially the auto tranni. My old 92  auto was the same, 16/17mpg with 235/75's and 30x9.5's. My 95 5 spd gets 29/30mpg with 31x10.5's.
A friend of mine with a jeep replaced an old tranni with a profesionally rebuilt unit, and instantly noticed a difference with his fuel milage.

The fact that it's a 4WD and the way I drive probably has a LOT to do with it too.  Putting the cone filter, Thorley header and larger high-flow exhaust really gave me a power boost, and I tend to use (maybe abuse) that power.  The fact that I can actually manage to pass a slow poke on the highway now, is a bit of a thrill.   

After i finished(for now) lifting mine... I thought i was having the same problem... crap mpg! I've just learnt to live with it I replaced the odd bit like sparks, dist etc, but no change apart from a slightly smoother running engine.

I get about 200miles a tank, 40lt tank, so i work that out as something like 19/20mpg. (US gallon = 3.79ltrs)

I'm on 32s, 8v, calmini / de-cat exhaust, stock gears...


If there is an answer, i'm listening!