Horrible Gas Milage, I cant figure it out!!!

[99GsxMD]

I have changed the spark plugs, spark plug wires, o2 sensor, and getting ready to cahnge the fuel filter... What could be the damn problem? It's getting really old only getting 200 miles to a full tank of gas. With gas at $3.20 ++++, i need to fix this. Any help would be awesome.

Also i just installed a FMIC, and it seems like everytime i shift into 3rd, 4th, 5th, my exhaust makes a loud pop, and seems to backfire. I dunno what that could be. I have a list of everything done to my car.

 

[tbonitz301]

It could be a number of things. You could have leaky valves, or running rich just to name a few. Do a boost leak test,compreesion and leakdown test to ensure the health of your engine

 

[siceclipse]

crack in the manifold or worn out exhaust gasket

 

[turbotalawd]

If you're backfiring like that in between shifts it definately means your running rich. Do you have your bov venting to the atmosphere?

 

[SOADweskey]

200 miles to a complete tank at 16 gallons or 200 miles until the fuel light turns on which in my car means 12 gallons.

My 2G GSX goes about 235 miles until the fuel light turns on (12 gallons so about 19.5 MPG) under normal driving conditions while having a little fun. It gets much better on long open freeway drives but city driving and stop and go freeway keeps it just below 20 mpg.

 

[Avionixx]

200 miles to a complete tank at 16 gallons or 200 miles until the fuel light turns on which in my car means 12 gallons.

My 2G GSX goes about 235 miles until the fuel light turns on (12 gallons so about 19.5 MPG) under normal driving conditions while having a little fun. It gets much better on long open freeway drives but city driving and stop and go freeway keeps it just below 20 mpg.

Same here. I get close to 21 mpg with mixed driving (half freeway and half street). Honestly, that's the best I've seen the car do; it used to do 16-17 mpg before I fixed all of the boost leaks. Of course my fuel trims are still towards the rich side, so hopefully I'll pick up a few more mpg when I get them dialed in.

 

[Defiant]

Come back when you've done the math and actually tell us how many miles per gallon you're getting.

Anything around 20 is normal for a stock torbo. If you've modded, it'll be less.