extremely bad gas milage?

Pull out the O2 sensors and clean them. The chances are that the tips are contaminated causing the sensors to malfunction and the engine to run too rich.

I agree with bullitt, I was getting 11mpg with my setup. I changed the O2 sensor last week and now I am getting about 16mpg which I think is normal for this setup. That is a combination of normal and WOT driving with mostly street driving.

If that gas sat for that long, some of it could have evaporated.

If not done already, pull codes. While O2's can cause poor mileage, so can a bad MAP sensor and a few others.

Good luck.

That's awful gas mileage. Change your fuel filter also. Add some air to all 4 corners to create less rolling resistance. Check your brakes and make sure nothing is hung up.
My pretty stock 94 Cobra gets 25MPG with some spirited driving mixed in.

Likely not the culprit but I think a non-functional EGR system hurts economy too.

Dumping The computer diagnostic codes on 86-95 Mustangs

Revised 19-May-2009 to update drawing for dumping the codes on 86-88 Mustangs with no check engine light.

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 way 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.

Be sure to turn off the A/C, and put the transmission in neutral when dumping the codes. Fail to do this and you will generate a code 67 and not be able to dump the Engine Running codes.

Dumping the Engine Running codes: The procedure is the same, you start the engine with the test jumper in place. Be sure the A/C is off and the transmission is in neutral. You'll get an 11, then a 4 and the engine will speed up to do the EGR test. After the engine speed decreases back to idle, it will dump the engine running codes.

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 Troublcodes.net Trouble Codes OBD & OBD2 Trouble Codes and Technical info & Tool Store. By BAT Auto Technical





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.



The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.

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



The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.


WARNING!!! There is a single dark brown connector with a black/orange wire. It is the 12 volt power to the under the hood light. Do not jumper it to the computer test connector. If you do, you will damage the computer.

What to expect:
You should get a code 11 (two single flashes in succession). This says that the computer's internal workings are OK, and that the wiring to put the computer into diagnostic mode is good. No code 11 and you have some wiring problems.

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.

Alternate methods:
For those who are intimidated by all the wires & connections, see Actron® 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 Digital Ford Code Reader (3145) – It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $30.

You have two choices:
1.) Dump the codes and probably find out what is really wrong.
2.) Throw parts at it, empty your wallet and get really disgusted with the car.

FitzC said:

dumped the codes today and got

with car running

Mass Air Flow (MAF) or Vane Air Flow (VAF) out of range - MAF VAF

and without

EVP - EGR not responding properly during test - EVP

Click to expand...

In order to give you the correct test path & fix, I need the exact code numbers.