lately i been getting 10-11 mpg...
 

ever since i got the car here in germany i havent seen a tank full make it past 150. i just thought it was because i got on the gas peddle too much.

when i first got the car here it had a bad exhaust leak. due to that exhaust leak it fouled out the plugs. so i did a tune up on the car...

i replaced: fuel filter, plugs, air filter, IAC and i was going to replace the o2 sensors. i decided to wait on those to see if any change would come from all the stuff i replaced. maybe i should of replaced the mid-pipe gasket i could still have a leak?

well there was no change at all. im still getting around 120-130 a tank full. im not getting into boost that much and been driving like a granny, i let smart cars pass me when im getting onto the auto bahn.

what do you guys think it could be? could an exhuast leak cause poor mileage?

The exhaust leak caused a bit of a mileage drop for me but mine was bad (as in, I couldn't use the HVAC everytime I stopped) but the mileage drop wasn't that drastic. It never hurts to fix it though. Just curious, did you get the car tuned for their higher octane gas? 93 here is 95 over there and I've seen it go as high as 100 over in Europe.

I got 12.5 mpg on my last tank, thats about normal for me, and Im N/A with all stock internals.

hows gas prices over in germany? Do they run higher octane at the pumps there or is it the same 93 or 91 , 89, 87??

Depending on miles dirty old O2 sensors and cause awful gas mileage. As will vacuum leaks.

i pay 3.4x a gallon on base, its about to surge up to nearly 4 dollars a gallon. euro octane reads higher 100 or 98 is really american rated 93 octane 95 is 91 octane and so forth. my junk is tuned for 93 octane and 91 (california) octane.

gas on the economy is stupid expensive 1.20-1.40 EURO a liter!!! 1 EURO = 1.5X US dollar. our cars take 50-55 liters to fill up from low fuel light.

i tightned up the exhaust leak on friday and my car is at 160 miles and the low fuel light hasnt came on, yet. so that has helped out a lot but now im sure my plugs are fouled out.

o2 sensors are old they have 90k miles on them

I would suspect that your 02's are the culprit. You have changed everything else and Mustangs are known for eating sensors. I also believe that 90K miles is way beyond the life expectancy of those sensors especially since you have done some modifications to the car.

My bad, read Wikipedia wrong.

02 sensors are supposed to be changed ever 100k according to the haynes book, but i just changed mine around 60k after i suspected them goin foul

im thinking that too but i havnet gotten any kind of CEL for a bad sensor, running rich, lean or anything like that.
i thought the same thing when i got here

this is the same i read around the internet about o2 sensors that they should be changed 80k-100k miles. mine have been abused...

im going to texas for about 30 days starting april 5th so im not going to order anything. i will just pick some up while im there or when i go to california to visit the folks. my list of pick up parts is growing friggin car is getting old and needs lots of little stuff. o' well keeps it interesting.

12 mpg on a stock motor? i get 18 mpg on a stock motor. Their must be somthing up with your car as well...12 mpg=NOT NORMAL