Horrible fuel mileage on my 5.0.

[50specialist]

Hey guys, I'm having a problem with my gas mileage. It's doing 10-12 mpg's. My car runs great and when I floored it a few times, no smoke whatsoever came out of the exhaust and no backfires. No misfire or any thing. Just horrible fuel mileage. Here are my mods: Offroad 2.5 inch x pipe, two chamber flowmasters, smog pump deleted, 65mm TB and EGR Spacer, BBK 1 5/8 unequal length headers, msd cap and rotor, taylor 8.2mm Thunder Volt wires, msd street fire TFI coil, K&N filter with air silencer deleted, and Pro-M 75mm mass air sensor calibrated for stock injectors(works perfectly). There is a small vacuum hose, which releases fumes that smells like gas. It doesn't reach the charcoal canister, so I guess it was part of the smog pump. I re-routed that hose to the engine compartment near the headers...


(just kidding )

It's in the fender, in front of the intake filter. No check engine light(the light works).

 

[magnj]

How hard are you getting on it...If your putting the pedal to the floor frequently in the city...you could have nothing wrong besides a lead foot.

 

[50specialist]

I don't step on it much. In fact, I don't have lead foot. How about the fuel filter?

 

[jrichker]

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 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.

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 EQUUS 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.

 

[Jaswir]

make sure you have no vacum leaks! Hook that one hose back up to the charcole boxs! Might as well change ur fuel filter! Takes 10mins! but check codes too

 

[50specialist]

make sure you have no vacum leaks! Hook that one hose back up to the charcole boxs! Might as well change ur fuel filter! Takes 10mins! but check codes too

Nice! I heard they sell OBD I scanners for a cheap price at Auto Zone. It's a 93' and I will check my codes. The weird thing is that the black hose does not reach the canister, unless it was connected to the smog pump, which I deleted. Thanks guys.