I have a 96 3.8 5Spd, people claim they get around like 25 or more on the highway w/ these, and im just not gettin it, I have a K&N airfilter, flowmaster exhaust, i changed the plugs to bosch plat 4`s, the wires still look good, not sure about the O2`s, ive seafoamed it, ran injector cleaner, so im outta ideas, any suggestions or some insight would be greatly appreciated. and my RPM`s @ 75MPH are 2500, does that seem right?

 

Tire Pressure matters,30-35 PSI is best.Engine temperatire below 180 degrees will drop economy.Try changing Fuel Filter/PCV Valve. How many miles on the motor? Oxygen sensors go every 50,000 miles or so..

 

I'm getting 25 MPG easy on the highway and I'm running 3.42's and an A4... Check your O2's, when was your last tuneup?

 

Dear God not Bosch +4s.

Biggest automotive waste of money I know of.

It could be a range of things NOT mechanical such as wind, driving style, traffic, city driving, etc.

 

wouldn't bad o2's give u an SES light?

 

Yes but an old one will still only perform half as good as a new one and still be functional enough not to send an SES...

 

100k on the clock, tune up wise im not sure, i did the plugs 4months ago, i know i got a lower degree stat in there, runs around 165 - 70, the o2`s i know probably are overdue, same ones since i bought the car 20k ago. fuel filters been changed, pcv has been changed, the coils i have no clue, wires no clue, i just changed the oil and added some risolone in there also.

 

Do the O2 Sensors,You will most likely see a increase in mileage.

 

how much would it cost to have a tune-up done? Mines at 100k, and i think its due for new plugs, wires, and o2s. How much do you think it would cost?