Hey all. Did some calculations and found that the speedo in my '91 F-150 is off by 4, almost 5 mph. Tires are "stock" size, Goodyear Wranglers P235/75R 15.

I know that I have a E4OD cause of the OD on/off switch on the dash, but the question is, does the speedo read straight off the cable or is there a "black box"?

If it helps I have the vin decode info here.

Also, the cruise works off vacuum, not Elec{?}.

If it's straight mechanical, I know how to change the little plastic gears to get it right.

If it's read thru a box, how does on adjust the speedo?

<table style="border: 1px solid rgb(153, 0, 0);" width="600" align="center"><tbody><tr><td colspan="2" style="padding-bottom: 5px; padding-top: 5px; padding-left: 15px;" align="left" bgcolor="#0099cc">World Manufacturer Identifier - 1st, 2nd, 3rd Positions: </td> </tr> <tr> <td style="padding-left: 15px;" width="25%">Manufacturer: </td> <td>Ford Motor Company, USA</td> </tr> <tr><td colspan="2" bgcolor="#0099cc" height="1">
</td></tr> <tr> <td style="padding-left: 15px;">Make:</td> <td>Ford</td> </tr> <tr><td colspan="2" bgcolor="#0099cc" height="1">
</td></tr> <tr> <td style="padding-left: 15px;">Vehicle Type:</td> <td>Truck (Completed Vehicle)</td> </tr> <tr><td colspan="2" bgcolor="#0099cc" height="1">
</td></tr> <tr> <td colspan="2" style="padding-bottom: 5px; padding-top: 5px; padding-left: 15px;" align="left" bgcolor="#0099cc"> Brake Type and GVWR Class - 4th Position: </td> </tr> <tr><td colspan="2" bgcolor="#0099cc" height="1">
</td></tr> <tr> <td style="padding-left: 15px;">Brake System: </td> <td> • Hydraulic brake system, Class E, GVWR 6,001-7,000 pounds, None</td> </tr> <tr><td colspan="2" bgcolor="#0099cc" height="1">
</td></tr> <tr> <td colspan="2" style="padding-bottom: 5px; padding-top: 5px; padding-left: 15px;" align="left" bgcolor="#0099cc"> Line Series, Chassis Type, Body Type - 5th, 6th, 7th Positions: </td> </tr> <tr><td colspan="2" bgcolor="#0099cc" height="1">
</td></tr> <tr> <td style="padding-left: 15px;">Line Series: </td> <td>F-Series - F150</td> </tr> <tr><td colspan="2" bgcolor="#0099cc" height="1">
</td></tr> <tr> <td style="padding-left: 15px;">Chassis Type: </td> <td>4x2</td> </tr> <tr><td colspan="2" bgcolor="#0099cc" height="1">
</td></tr> <tr> <td style="padding-left: 15px;">Body Type: </td> <td>Supercab</td> </tr> <tr><td colspan="2" bgcolor="#0099cc" height="1">
</td></tr> <tr> <td colspan="2" style="padding-bottom: 5px; padding-top: 5px; padding-left: 15px;" align="left" bgcolor="#0099cc"> Engine Type - 8th Position: </td> </tr> <tr><td colspan="2" bgcolor="#0099cc" height="1">
</td></tr> <tr> <td style="padding-left: 15px;">Engine: </td> <td>5.0(302cid)</td> </tr> <tr><td colspan="2" bgcolor="#0099cc" height="1">
</td></tr> <tr> <td style="padding-left: 15px;">Cylinders: </td> <td>V-8</td> </tr> <tr><td colspan="2" bgcolor="#0099cc" height="1">
</td></tr> <tr> <td style="padding-left: 15px;">Fuel Type: </td> <td>Gasoline</td> </tr> <tr><td colspan="2" bgcolor="#0099cc" height="1">
</td></tr> <tr> <td style="padding-left: 15px;">Horse Power: </td> <td>185</td> </tr> <tr><td colspan="2" bgcolor="#0099cc" height="1">
</td></tr> <tr> <td colspan="2" style="padding-bottom: 5px; padding-top: 5px; padding-left: 15px;" align="left" bgcolor="#0099cc"> Model Year - 10th Position: </td> </tr> <tr><td colspan="2" bgcolor="#0099cc" height="1">
</td></tr> <tr> <td style="padding-left: 15px;">Model Year: </td> <td>1991</td> </tr> <tr><td colspan="2" bgcolor="#0099cc" height="1">
</td></tr> <tr> <td colspan="2" style="padding-bottom: 5px; padding-top: 5px; padding-left: 15px;" align="left" bgcolor="#0099cc"> Assembly Plant - 11th Position: </td> </tr> <tr><td colspan="2" bgcolor="#0099cc" height="1">
</td></tr> <tr> <td style="padding-left: 15px;">Assembly Plant: </td> <td>Kansas City; Claycomo, Missouri</td> </tr> <tr><td colspan="2" bgcolor="#0099cc" height="1">
</td></tr> <tr> <td colspan="2" style="padding-bottom: 5px; padding-top: 5px; padding-left: 15px;" align="left" bgcolor="#0099cc"> Production Sequence Number - 12th - 17th: </td> </tr> <tr><td colspan="2" bgcolor="#0099cc" height="1">
</td></tr> <tr> <td style="padding-left: 15px;">Sequence Number: </td> <td>A05044</td></tr></tbody></table>

 

I did it following these instructions in my 94.

Programing for tire size,

Locate the connector at the bottom of the instrument panel below the center of the glove box. Should be LB/Y, has "PSOM" printed on the connector in white lettering. Held in place with a plastic retainer.

Insert a jumper wire or alligator clip in service wire and clip other end to vehicle ground with the key in the OFF position.

Turn key to RUN while holding down the trip odometer RESET button on the speedometer.
Release RESET button The Speedometer will prove out(sweep across dial and back). The English/Metric and revision levels will be displayed. The last number of the display id the dealer mode lockout count. This count shows the number of allowable conversion constant changes remaining. When the count is zero (0), no additional changes can be made to this instrument cluster. If a revisions required a service instrument cluster must be ordered.
Press and release RESET button again and PSOM conversion constant without the decimal point will be displayed followed by the word CAL.

Press and release the odometer SELECT button as many times as necessary to change the conversion constant to the correct value. The constant will only increase (not decrease) when the SELECT button is pressed so reducing the constant means counting up until the constant jumps to the bottom of the scale and begins counting up from there.

Pressing and releasing the RESET button to lock in the new conversion constant reduces the number of times the PSOM can be reprogrammed by one count. If you change your mind and want to go back to the old conversion constant, turn the key OFF BEFORE you lock in the new constant.

 

That won't work for me, don't have a digital trip meter or odometer.

 

Ok yea they changed it in 92 to full electronic, I wasn't sure of the exact year they did so.

Your speed sensor will or should look like this, combination mechanical and electronic. Cable drive with a VSS for the computer.

http://www.rockauto.com/catalog/moreinfo.php?pk=932794

You'll need to get the right gear for the end of it, examples here

http://npd.dirxion.com/WebProject.as...Code=fod09flx#

I was afraid of that, the direct link (second one) to the page didn't work.

Use the National parts depo link at the left side of the page here in FTE and then check out page 107.

 

Thanks. now i know which way to go.

Local Dealer keeps the gears in stock.

Went thru this with my '82 and they knew which one i needed to get it right.

Thanks again.