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Discussion Starter #1
I own a 1995 Mustang GT 5.0L automatic, it runs very smooth and is decently fast. But i have been getting the most terrible gas mileage since i bought it. it consistently gets 13 mpg and 14 if im lucky, i know these cars should be getting 17-18 in town and like 22-23 on hwy. i have not done anything to it engine wise other than a bbk cold air intake, bbk offroad x pipe, flowmaster 40 series mufflers. I have a pretty good amount of car knowledge but i am at my wits end. here is what i have done to try to correct the problem.

-new o2 sensors
-Spark plugs and wires
-cleaned air filter
-checked timing (it was retarded to 8 btdc i reset it to 10 btdc)
-changed fuel filter (the old one had what looked like used oil in it haha so i know it was time for a change).
-cleaned MAF sensor and throttle body.
-made sure my tps was set adjusted to .98v-.99v
-new fuel pressure regulator
-new engine coolant temp sensor
-new thermostat
-oil change
-drive like my grandmother.

love my car hate the mileage.
 

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Check injectors, are they leaking. Leaking injector may be clogged and has bad spray pattern. If exhaust gas analyzer shows plenty of O2, you have a vacuum or exhaust leak which gets engine too rich. Does brakes drag, transmission/converter ok? I have 94 cobra, and all aroung mpg is about 21
 

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I get around 23 highway... I dont do a lot of city driving but 13 sounds really low to me, I would expect like 17 in town. Unless you are popping wheelies every corner lol
 

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Discussion Starter #7
Check injectors, are they leaking. Leaking injector may be clogged and has bad spray pattern. If exhaust gas analyzer shows plenty of O2, you have a vacuum or exhaust leak which gets engine too rich. Does brakes drag, transmission/converter ok? I have 94 cobra, and all aroung mpg is about 21
i get 16 hwy mpg. no exhaust leak and im pretty sure no vacuum leak i wish i had a diagram for the vacuum lines. currently running a bottle of seafoam through it to see if itll help any.

and no 13 is not normal its a 5.0 not a big block 460 or something. this is my 3rd 5.0 and i got 18 in town and 23 on hwy with all. im running out of stuff to fix.:baller:
 

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Subbed to this just in case somebody posts up a diagram for the vacuum lines.
 

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Never mind I got bored so I found it. It's for a fox but it should be pretty much the same.

 

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Discussion Starter #11
just thought id update. i have fixed the problem. there is a vaccuum line that runs from the gas tank to the charcoal canister inside the front passenger fender then into the canister purge solinoid then to the upper intake. the piece that runs from the canister to the solinoid and from the soliniod to intake had dry rotted and had holes in it. this was allowing my gas and fumes to evaporate. it required me to take my upper intake off to get to the nipple that the vaccuum line connects to but on the first tank after replacing the 10 dollar vaccuum line the car got 18.8 in town and 22.2 on the highway!

thanks for all the suggestions and keep driving
 

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just thought id update. i have fixed the problem. there is a vaccuum line that runs from the gas tank to the charcoal canister inside the front passenger fender then into the canister purge solinoid then to the upper intake. the piece that runs from the canister to the solinoid and from the soliniod to intake had dry rotted and had holes in it. this was allowing my gas and fumes to evaporate. it required me to take my upper intake off to get to the nipple that the vaccuum line connects to but on the first tank after replacing the 10 dollar vaccuum line the car got 18.8 in town and 22.2 on the highway!

thanks for all the suggestions and keep driving
I know this is an old thread, but I just wanted to say thanks for posting this! And also thanks to those who posted the vacuum line diagrams.

I recently bought a 1995 GT Convertible. 76,000 miles on the clock. Clean as a pin inside and out for a 25 year old car. Just has a rear main seal leak and also was getting 10 miles per gallon! I racked my brain trying to figure out why my gas mileage would be so bad. 150 miles per tank isn't normal. Thanks to this thread I discovered that my vacuum line from the charcoal canister to the purge solenoid and then to the back of the upper intake was disintegrated and trash! Spent a few hours and $57 bucks replacing fittings and lines and now she's getting normal gas mileage again! On pace for 250+ miles per tank just like I remember!

225568
 
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