I just bought my first Powerstroke, a 97 4x4 with 295-75 tires and the speedometer is off almost 20%. Someone told me you tune Powerstroke speedos with a computer, not by putting another gear in them. Also how do I tell what backend ratio I have?

 

Yes the speedo can be re calibrated at the instrument cluster. You can find instruction on this site
Tips - Idea - Hints

For the gear ratio look at the build sticker on the door jam or door. there will be a block labeled axle code
C5- limited slip 4.10
C9- limited slip 3.55
35- open diff 4.10
39- open diff 3.55

 

"First, you'll need to know the actual height of the tires, not the
nominal height of 35" that's printed on the sidewall. To get that,
make a mark on the edge of the tire at the ground, and mark the ground
directly under the mark. Now, roll the truck far enough for the tire
to have made three revolutions. When your mark on the tire is at the
very bottom, near the ground, mark the ground again, and measure the
distance between the two marks on the ground. Divide that distance by
three, since there were three revolutions of the tire, then divide
that number, (which is the circumference of your tire,) by 3.14. The
answer you have is the true height of your tire. Write that number
down, because you'll need it for the next step. Divide 30282 by your
actual height. If your true height is 34", the math goes something
like this: 30282/34=891. That would be your speedometer calibration
code."

"To set the calibration, ground the single wire connector under the
glove box it says PSOM (Programable Speedometer Opdometer Module).
"Yes there is only one and it has a spade type plug on the end". I
used a wire with clips on both ends to ground the plug to a screw
under the dash or try a test light and use the clip end to the PSOM
and the other jam in a dooe hinge. Now look at your speedometer on the
face of your dash while sitting in the drivers seat and there should
be a "reset" button and a "select" button. While holding the reset
button in on the trip meter, turn the ignition to 'on' while the wire
is still grounded. Let go of the reset button. The speedometer display
will sweep once and will show a code of some kind then push in again
the "reset" button and the existing code will be displayed with
RECAL?, mine said 976 RECAL? Now you enter your new code you came up
with by dividing the rolling measurement by PI or 3.14 by pushing the
"select" button until it gets to the new calibration code number. You
may have to push "select" a whole bunch of times until you get to your
code. If you turn off the key at this point the original code will not
be changed or any of the 6 lives will not be used. To store your new
code press "Reset". Turn off the key. Unplug the ground wire."

 

Blue Mule nice write up. reps sent

 

the question is whether or not it was him... kinda looks like steve baz...

 

Ok, I did everything just like it said, but when I got to the speedo part, I grounded the wire, used a test light to be sure it was grounded, then held the reset button while turning on the ignition. The speedo swept, then displayed some crap like E0 08 or some crap, then when I pushed the reset button again, it displayed 1020CAL . I pushed the select button and it wouldn't change at all. SO NOW WHAT?????

 

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it might mean that the PSOM has been reprogrammed its 6 times already and you can't change it. I would try it a second time and see what happens.

 

Mine says EO 06 and as I understand it everytime you reprogram it, it counts down ... EO 05 etc. until EO 01 at which point no additional programming can be performed.

 

.....X2.....

 

Yeah right! Steve never wrote anything.Spend some time and read some of the stuff on his website. Plagerism is the word that comes to mind. He copied almost all his material from other peoples websites and posts on what used to be Ford-Diesel.Com

 

So what do I do if its times are up?

 

..Time for a new PSOM...