on my IROC nothing major as far as mods...just what's in the sig and it only gets about 10mpg if that mostly city though but I'd still figure to get around 15?? Am I wrong????

 

I get around 18 on the freeway and about 10 around town, I have heard of people getting a fair amount better. I have been told to replace my 02 sensor, do a complete tune up, make sure my timing is set right, make sure TPS is set right, replace my cat and then see what I get. I haven't done it all, but the complete tune up, and TPS didn't do much of anything for Mileage. I also was told that modified MAF's can hurt gas mileage a little, as well as older MAFs, so I would like to replace mine. I still haven't completely solved the problem tho, and I expect somewhere around 23-25 freeway and atleast 15 around town... Not to mention I have a 305. Something just isn't right...

 

Do a full tune up first. Spark plugs, wires, cap and rotor, O2 sensor, 2 or 3 'gas-ups' with good fuel system cleaner, TB cleaner, air filters, oil and oil filter, fuel filter, pcv valve, check all tire pressures and set to spec, alignment.

Use good fuel system cleaner. Redline Si-2 worked for me, after 4 treatments I picked up about 1 mile to the gallon... still driving hard and fast so I can get even better I am sure. I have also heard great things about Seafoam additives. Stay away from generic stuff like STP, Slick50, etc.

The PCV valve is an important player in gas mileage... mostly overlooked it should be changed out every other oil change ideally. It scavenges air and fuel mixture from the crankcase which will keep oil cleaner and also "find" air/fuel to combust for gas mileage.

If all of this does not help (and it really should), I would replace the EGR system. They can go bad after 10 or so years and that'll definitely affect gas mileage.

Good luck! I started out getting about 12 mpg, and now after full tune up like above I am getting about 14.5mpg. This is mostly city, some highway.

 

Does the jet chip compensate for the larger 24lb injectors? I hear if you run larger injectors on a stock prom it will run rich.

 

To be honest I'm not sure about the chip/injectors
It did pass the emission test so I assume it's not running too rich