Korishan

I have a problem with full efficiency, which the title implies.
When I first got the car a couple months back, the first tank of gas I got about 18mpg. I just had to dog it run 100mph+ down the back roads.
The second and 3rd tank I got like 22-23mpg because I live 1 mile from work and didnt go anywhere other than work and home.
Then I let the guy who previously owned it borrow it for a month, and when I got it back, I filled it up the 2nd time after getting it back, it still had about 22mpg avg.

Now, I get 12-13mpg after I have done the following:
1 can of Sea Foam with 1 tank of gas. Ran through, dont remember the mpg on that tank, I know it was low and I had hesitations on acceleration.
Also, I took out the stock air filter and replaced it with the K&N air filter. Same basic shape and everything.
And changed the oil and filter (10W30), and the transmission oil and filter (Mercon III).

Now, after that little bit of changes, I now get 12-13mpg. What the hell!?!?!?

Can anyone explain to me why allowing "more" air flow to the chamber uses 45% more fuel?? Or is there something else someone can recommend the problem being?


Also, another thing I have noticed, my amp meter keeps dropping a few times durning idle and cruising. Which, I have noticed I "feel" a "slight" hesitation in the movement of the car, could that make the gas mileage go down too?

wwmost

umm did you put a whole can of sea foam in your tank? did you run it till empty before filling it up? only thing i can think of is that there is still sea foam in your tank and thats why you are getting the hesitation and bad gas. run it to empty and a little more. then go to a reputable gas station and put some fresh gas in there. see what happens.

Matts00GT

Well the reason it requires more fuel is because you have to have a certain ratio of air to fuel to get a good burn. However, it def. should not be that drastic of a drop. Usually you actually see small gains in MPG.

Since you have a slight hesitation, I want to say it's probably a misfire. Check all 8 plugs. What some people don't understand about fuel system cleaners and fuel injector cleaners, is that it makes the car run "hotter." I.E. it burns hotter than just regular 87 octane. Check the plugs and maybe replace them.

GT_Bob

I'd do a thorough visual inspection of all your vacuum and sensor lines. Possibly you pulled one off changing the filter.

The filter would not cause a drop in mpg like that.

The SeaFoam shouldn't have caused any problems at all.

Your amp meter will drop at lower-than-normal idel.

BoBalls08

and another thing, DON'T LEND OUT YOUR CAR BRO!!!!!!

03blkstang

+1 ESPECIALY TO THE PREVIOUS OWNER!!!

4.698GT

Did you change the fuel filter?

stang2000

Yeah **** that lending out to the previous owner. **** him, lol He/She evidentally didn't want the car or they wouldn't have sold it. Why in the world would you lend to him/her for a month even?

Anywho, check those vacuum lines like suggested and the plugs.

czwalga00gt

Go somewhere far... fill it up set the cruise control for about 4hours. See what your MPG is. Lead foot is a big cause of mpg loss. Tough cure though.

Korishan

Well, the reason the previous owner parted was because he had knee surgury and was unable to drive the mustang comfortably. The reason i let him use it for a little bit was because his "good" car was having electrical problems and took him a little bit to fix them.
I've ran 3 tanks of gas since the sea foam. I have not replaced the fuel filter as of yet, and haven't looked at the plugs. Those damn plugs are hard to get to on the passenger side, tho.
A little low air in the back tires wouldn't have much drop in mpg, either, would it? I noticed today today they looked about 10lbs low.
And, I only get gas from new gas stations that installed new tanks. Less chance of water or crap in the gas. So far, the only gas I've put in was Kangaroo and Shell (I think it was). Both of which were built within the past 6 yrs.
Also, I run with 89, not 87. I filled up on 89 the first day I had it, and only put 89 in since. So I can't see how all of a sudden it'd be the octane dropping my mpg.

I'll check the plugs now, since i still have some daylight.