OK so right now im getting about 12-14mpg. Only mods to my car are 2600 stall converter, CPT trans, SLP CAI, Mac midlenth headers, SLP catback, !cat. I know my EGR is faulty since its throwing a code, and im pretty sure my air filters need to be cleaned/changed, but could that really kill my gas milage that much. Shouldnt I be getting closer to 25mpg?

 

I would definetly change the air filter. Also its a silly question but how heavy is your foot? And it should get better the ta in my sig would get atleast 18. Oh and make sure you dont have any header leaks, vacume leaks, and maybe change the spark plugs if they are old.

 

Under what driving conditions are you getting 12-14mpg? In heavy traffic, stop-and-go, that's not all that low. On the freeway, at 2,000rpm or less, that's a little more than 1/2 of what you might expect. Its not likely you would see 25mpg overall, unless you only drive freeway, in overdrive. Does your converter lock?

Depending where you live, you may find a small drop off in the winter, when they switch to an oxygenated fuel blend.

 

OK, sorry it took so long to answer this, busy week at work. Anyway. Id say about 80% of my driving is 45mph+ and on the freeway. I dont have a heavy foot at all, never hard on it at all from a stop. I live in the Philadelphia area and my converter does not lock. Oh and my plugs have about 800 miles on them.

 

What grade gas do you use?

Any signs of misfires?

Any signs of exhaust leaks?

How old are the O2 sensors?

If the converter is non-locking, is there any signs of slip in the trans?

 

in bold

 

Injuneer, correct me if im wrong, trying to get back into the lt1s and seem to have forgetten some things. My TA with the motor in my sig got 18 mpg(roughly on the highway) with an open loop tune and didn't even run o2's. Could you just unhook the o2's thus putting the car in open loop and see if it does any better. Or do you have to have an open loop tune for it to work? I would be an easy way to check if it would work.

Oh and another silly question, but do you always fill the car completely up or do you let the pump stop its self. I do know that not all pumps stop at the same level and can make you mpgs off.

Definetly check for vacume leaks. Its amazing how a crack/unplugged hose can affect the way a car runs.

 

always fill it, then top it off.