Gas Mileage Problems

It can come down to driving style and state of tune, the former of which is very subjective.

Have you pulled codes to make sure nothing is in there? How old are the O2s? How far do you bury the loud pedal? How far do you drive in a given stretch?

Good luck.

It sounds like a tune up would help ya out, if not directly with milage, with tractability.

Jrichker posts links on yanking the codes. He will probably see this and post the links in the morning (I am too tired to look it up and link to it. A search under his username would reveal the same info, as he posts the info often).

They say HEGO's are good for ~50K (EGO's are good for a good bit less. We have HEGOs). You can use a meter to see how fast they switch and get an idea of their amplitude if you feel like it. They are about 40-45 bucks each and a 5.0 uses two.

I would probably do a tune up, omitting the O2's and then see how it does. You can always do the O2's later (I only say this because of their cost). The opinion of others will vary. Knowing codes info would help a lot.

Good luck.

Hissin makes some very good suggestions, as always.

Get comfortable with checking the trouble codes. This should be the first thing you do anytime you have a concern. It can make life much easier.

The second thing I would do is pull the superchip. Years back I had one of these, and did not see much improvement from it. It may be adding too much fuel for your mods.

A liitle late in the day, but still here...

Dump the codes and see what the computer says is wrong…

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.

See http://www.troublecodes.net/Ford/
OR
See http://www.mustangworks.com/articles/electronics/eec-iv_codes.html

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.

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 Walmart.

Or for a nicer scanner see http://www.midwayautosupply.com/detailedproductdescription.asp?3829 – It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $35.

jrichker said:

A liitle late in the day, but still here...

Click to expand...

You are right on time - it is the morning somewhere in the world.

I am used to you coming in at about 4-5 a.m. [my time] and mowing down all the threads with your excellent replies.

foxstang9050 said:

so im guessin a good idea would be sell the superchip and get some ud pullies

Click to expand...

That seems like it is out of left field to me.

I would systematically go through and check out maintenance items rather than tossing (or removing) random parts.

Just my thinking. Good luck.

i wouldn't look past the fact that youre fuel system might be really dirty.
i dont mean to sound like mr. lubetech here, but in grease monkey where i work, 70% of the time people are getting bad gas milage, is because their fuel system needs to be cleaned, i.e fuel filter, tarnish in the fuel lines, eccesive carbon buildup on the throttlebody, and intake plenum. i would start there, being that its the cheapest option, you never know, it could be something as simple as an old fuel filter, or carbon buildup. if i were you, id start with that first.

It *could* be other stuff you might not necessarily think of.
Tyre pressures, alignment out of whack, brakes dragging, things like that.

I would sell the superchip anyway. Most chips only advance the timing, would you could do anyway and your combo isn't radical enough to need a chip.

foxstang9050 said:

ok so this is what i got from pulling the codes... i think

1)Readout Memory Test Failed
2)Ignition Diagnostic Module (2.9L, 3.0L & 4.0L)
3)AXOD Converter Bypass Clutch Not Applying Properly

Not quite sure what that means and im not sure if i read the codes right but can anybody help me with these?

Click to expand...

The discriptions are of little value, you need to post the actual code numbers the computer spit out. Please repost the code numbers and I will try to help you.

foxstang9050 said:

ok i used the check engine light but im not sure if i
read them right. I think i got 15, 16, and 39. I read them as 15= one blink,
pause, 5 blinks, 16= one blink, pause,6 blinks, then 39= 3 blinks, pause, 9
blinks... am i reading them right?

Click to expand...

Code 15 - No Keep Alive Memory power to PCM pin 1 or
bad PCM (Memory Test Failure). The voltage to the Keep
Alive Memory (KAM) is missing (wiring problem) or the KAM
is bad. The KAM holds all of the settings that the
computer "learns" as it operates and all the stored error
codes that are generated as a result of something
malfunctioning while the engine is running. Use a voltmeter
to check the voltage to the pin 1 on the computer - you
should always have 12 volts. No constant 12 volts = bad
wiring. If you do always have the 12 volts, then the KAM is
bad and the computer is faulty.

Note that some aftermarket chips will cause code 15 to
set. Remove the chip, clear the codes and retest.

Before replacing the computer, remove the battery ground
cable for about 20 minutes. This will clear all the codes.
Retest after several days of running. If the 15 code is
gone, then don't worry about it. If it is still there, then you
get to do some troubleshooting.

Wiring diagrams for the proper model years are next…

For 86 models see http://www.autozone.com/images/cds/gif/large/0900823d80167158.gif

For 87 models see http://www.autozone.com/images/cds/gif/large/0900823d8016715e.gif

For 88 models see http://www.autozone.com/images/cds/gif/large/0900823d80167162.gif

For 89-90 models see http://www.autozone.com/images/cds/gif/large/0900823d8019595f.gif

For 91-93 models see http://www.autozone.com/images/cds/gif/large/0900823d80195960.gif

Code 16 - Electronic ignition - IDM circuit fault - Ignition
Systems. Bad wiring, possible bad TFI. The computer isn’t
seeing the proper IDM signal coming from the TFI circuit.
There is a 22,000 ohm resistor in the dark green/ yellow wire
that goes to pin 4 on the computer. Disconnect the TFI
connector and remove the passenger side kick panel.
Then loosen the 10 MM bolt to disconnect the computer
connector. Use an ohmmeter to measure the resistance
between pin 4 and the dark green/ yellow wire on the TFI
connector. You should see 21 - 23 K ohms (21,000-23,000
ohms). If not the dark green/ yellow wire is broken or has a
bad connection. If this checks out OK, measure between
the dark green/ yellow wire and ground. You should see 1 M
Ohm or more, OR an infinite reading. Less that 100 K ohms
means a short to ground somewhere in the dark green/
yellow wire.



Looking at your car year and mods, I can't find a valid
description for a 39 code. They all come up with a AODE
(Automatic OverDrive Extended) - Transmission Torque
Converter clutch not engaging. You have an AOD,
and there is no connection between the Automatic
transmission and the computer for your model car.

The real answer to that is to troubleshoot the problems and fix them. Anyway you cut it, they will hurt the car's performance.

The code 15 means that everytime you shut the car off, it forgets all the settingsit learned during the adaptive learning process. That's got to hurt the mileage.