rusty88lx

used to get at least 20 mpg. put in a new radiator, tune up, flowmaster cat back, and i now get about 9 mpg. tried new thermostat and coolant temp sensor. i still make it through emissions but i would love to know whats going on

JPJP

These may be basic questions but the have to be asked: Have your driving habits changed? Is the ambient temperature lower lately?

tohoopty

very odd

FORD TOUGH

The additives in the winter gas will hurt your mileage some but not 11 mile to the gal. have you check for codes?

kevano

In general when you change any car from stock specifications you are taking what the manufacturer has optimized and taking it down a notch. Everything is in tune, so changing anything, even if its "high performance" or claims to "save gas" in my opinion hurts what has already been all added up and deemed the best combination for not only gas mileage, but for decent bang for buck, as are the fox body mustangs. I am only 20 however having asked alot of different mechanics stupid questions when I first started getting into fox bodies around 15, 16, exchanging parts they say hurts what is already optimized for best all around MPG, performance, drive ability, etc. My guess is the tune up, what spark plugs, etc think what did you use that might not be igniting all of the fuel going into the chambers. Or...what might be stopping the fuel going into it that could be cleaned, unclogged, etc air-wise, fuel-wise, etc. Also the exhaust is most likely bigger, the headers on fox bodies are pinched so when you open them up, yes, it is more efficient on the exhaust side, but on the intake side have you optimized the air/fuel ratio, how it burns, etc? These are general questions but my guess is not adjusting the rest of the engine and systems in sync with the new parts, and a regular tune up does not do the job.

Speed-Demon

try running a bottle of injector cleaner through it, it always helped my buddies 86 gt.