Fuel Economy In The Gutter


Oct 4, 2005
What's up everyone. My 93 GT is only getting about 10 or 11 miles per gallon. The car is stock except for BBK headers, H-Pipe and flowmasters. I replaced the spark plugs, plug wires, cap, rotor and fuel filter. What else can I do to try to squeeze more miles out of a tank. I know these cars are meant to be driven hard but I have had a couple of other ones in the past and they have not been this bad. Any ideas? Maybe the O2 sensors??? Any advice or info will be greatly appreciated. Thanks
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like said, dump the codes and definitely change the O2 sensors. they dont last forever.I also noticed that you did not mention the air filter. is it changed? are plugs gapped right? timing set right? fuel injectors may need to be cleaned, PCV replaced? vacuum leak?
1) Dump the codes (it's free to check)

2) If the O2s have 50+k miles (or you have no clue how many kms are on em), replace em. Even if you don't get any O2 sensor related codes.

3) Get the timing checked if your not sure what it's set to

I fixed a fuel related code last summer and replaced my O2s resulting in about a 5MPG increase. My fuel savings will long outweigh the $80 shelled out for 2 O2s.
Dump the codes and see what the computer says is wrong…Codes may be present in the computer even if the Check Engine light isn’t on.

Here's the link to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.

See http://www.troublecodes.net/Ford/



If your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.


89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.


Codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

For those who are intimidated by all the wires & connections, see http://www.actron.com/product_detail.php?pid=16153 for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Wal-Mart.

Or for a nicer scanner see http://www.midwayautosupply.com/pc-7208-90-equus-digital-ford-code-reader-3145.aspx – It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $30.
I gapped the plugs to factory specs. I haven't check the codes on it. I will try to get to that tomorrow. I am definitely going to replace the O2 sensors cause I have no idea how old they are. Other than that I can't imagine it being much else. How badly will the PCV affect it? I am going to flush the injectors out and check the timing to see if it helps. I am only getting about 160 miles to the tank. Thank you all for your help.
I've never had PCV problems with the stang so I can't comment MPG wise. But, on other cars with clogged PCVs it'd cause the car to idle rough and sputter. If your car isn't doing that, I wouldn't worry about this area to much.

You can also seafoam the engine, if you think things might be clogged up. Do a 'Seafoam' search in this tech forum, for more detail.

Is it the stock 3.08/3.27 gearing in the car? If so, 240-290miles per tank (17-20MPG) is attainable depending on your foot and city/hwy driving. If the gearing is higher, your fuel mileage will drop accordingly. I'm happy to get 220miles a tank, with my 4.10geared small bolt-ons Fox (approx 15mpg).
You need an accurate way of calculating your fuel economy. Just taking the number of miles per tank means nothing.

I only get about 200 miles per tank in mixed city/country road driving with my car according to the gauge. But then i fill it up and can only fit 12ish gallons in the tank!!!! So that leaves me with 16-17mpg. On highway trips i get 270-290 miles to the tank....again i can only fit 12+ gallons in the tank when the fuel gauge says empty. And 22-24mpg on a stang with 3.73's and an HCI package aint too bad.

You need to get us accurate data.
I have been real easy on it as I was trying to squeeze the most mileage out of it. I know that when you fill the tank you only put in about 12-13 gallons but with a full tank, regardless of how many gallons you put in I am only getting 150 miles per tank. That's way below what it should be. I have the stock gears (2.73 I think). I am at 1800 RPM or so at 80 mph. It was obviously a little higher when I had the AOD in it. I will be troubleshooting some of it tomorrow.