reseting speedo meter conversion constants ??

[7.3 powerstrok]

i changed the gears from 4-10 to 355 ,and from 32 " tire to 30" tire ..the orinagal cc was 980 i changed it to 10.65 ,now the abs e4od trans ,355 gears ,30"tires ,what is the ideal cc?

 

[idiabuse]

WTH are you talking about? Im subscribing to this one to hear some other replies.

I have shorter tires 30inch and change and had 235/85/16 tires before so my speedo is off also, about 5mph fast



Javier

 

[7.3 powerstrok]

ok my truck was shifting to quick after changing gears and tires ,so to reset conversn constant wich is teh configureation that the computer uses to operate ,the fumula is arrived at by turns in one mile ,my ford book has a chart and you can find the chart on line also ,example tire size 32"-235/85/16 =653 rev per mile ===conv-const is 980 ...to set find the plug under dash psom brown plug white letters..jumper wire to ground ..hold down reset button ....turn key on...release button the needel will sweep across and back ..the odom will display numbers ...press reset again the conv const will display ....press select to change the numbers to the number you need to be set at ,,you will need to press the select button many times to get what you need goes down to 600 then back to 1100 ...you can only reset up to 6 times so be sure ..once you select the number you need press reset ...turn key off ..remove ground from plug ...

 

[79jasper]

WTH are you talking about? Im subscribing to this one to hear some other replies.

I have shorter tires 30inch and change and had 235/85/16 tires before so my speedo is off also, about 5mph fast



Javier

He's right. But I'm not sure what year it started. I think with the powerstrokes. Look under your glovebox for a single wire plug end with PSOM written on the side.
My 94 5 speed has it.

 

[460mudsports]

You must be registered for see images attach

You must be registered for see images attach

This started in all F-series in 92 with the digital odometers. The information below was taken directly from a 95 Ford service manual.


PINPOINT TEST F: SPEEDOMETER/ODOMETER READS INACCURATELY


F4 VERIFY CONVERSION CONSTANT AND DISPLAY TYPE


l Check tire size and type or vehicle rear axle.

-- Refer to «Conversion Constants Charts» under Specifications in this section and note conversion constant.

l Check whether the conversion constant in the speedometer is correct with the following procedure:

-- Press and hold the RESET button on the front of the speedometer while turning the key to RUN.

-- Release the RESET button. The pointer will prove out and some codes will appear on the odometer display. If an "E" is on the left side of the display, the module is programmed for English display mode and should have English graphics (mph). A lower case "o" signifies an overseas (metric) graphics (kph). Verify the graphics and display modes agree. (The number appearing after the type is the microprocessor revision level and is not used in this test.)

-- Press and release the RESET button again. The conversion constant and the word CAL will be shown on the odometer display.

-- Verify the programmed conversion constant is the same as that displayed on the chart. Refer to «Conversion Constants Charts» under Specifications in this section.

-- Turn off the key to exit this test.

l Is the programmed conversion constant the same as that displayed on the chart and does the programmed display mode match the speedometer graphics? Refer to «Conversion Constants Charts» under Specifications in this section


Yes
REPLACE instrument cluster as described in this section. VERIFY proper operation.

No, conversion constant wrong, programmed display mode OK.
RESET conversion constant. REFER to Reset Conversion Constant in «F5».

No, conversion constant OK, programmed display mode wrong.
REPLACE instrument cluster as described in this section. VERIFY proper operation.




F5 RESET CONVERSION CONSTANT


l Reprogram speed conversion constant using the following procedure:

-- Locate the dealer mode programming enable single-terminal connector. The connector is located at the bottom of the instrument panel below the center of the glove box. On all vehicles, the dealer mode enable wire is Circuit #567 (LB/Y).

-- Insert metal clip in service wire panel connector. Clip other end to vehicle ground while the key is in the OFF position.

-- Turn key to RUN (not crank) position while holding down the trip odometer RESET button on speedometer. Release RESET button.

-- Speedometer will prove out (sweep across dial and back). The English/Metric and revision levels will be displayed. The last number of the display is the dealer mode programming 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 conversion constant change is required, a service instrument cluster must be ordered. Refer to this section for ordering information.

-- Press and release RESET button again and PSOM conversion constant (without the decimal point) followed by the word CAL.

 Press and release the odometer SELECT button as many times as necessary to change conversion constant to the correct value.
 NOTE:
 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. The module can only be reprogrammed six times. If you change your mind and want to go back to the old conversion constant, turn the ignition switch off before you lock in the new constant.

 -- When the correct new value is displayed in odometer window, press and release the RESET button to lock in the new conversion constant.

 -- Turn the key off and remove the ground wire. Verify proper speedometer operation.

 -- Is conversion constant now set to the desired value?

 NOTE:
 The module can only be reprogrammed six (6) times.



Hopes this clarifies.

Ronnie

 

[homelessduck]

What would mine be for a 285 tire and 3.55 gears? I couldn't find it. I've been meaning to reprogram it.

 

[7.3 powerstrok]

980 should get you on target ,also you may need to drive 10 miles after the reset ...the odometer measures over a 10 mile dastance to program

 

[homelessduck]

Thanks! ! How is that calculated? I found some charts but I ended up with different numbers. It's tire revolutions per mile X .0135 (15" wheel) correct? That would make mine 8.86.

I'm not meaning to question you, I just want to be sure since you only get to change it 6 times ... which seems pretty stupid.

Edit: You're right .. I forgot I have 16's. So it's 656x.015=9.84.

 

[RLDSL]

You only get to change it 6times because they want to sell you a new part with an expensive service job. Where have you been for the last 30 years

 

[Dave 001]

Just a comment.....gear ratio has absolutely no affect on the conversion constant. Tire diameter is the only thing that affects the conversion constant. The VSS only "sees" things down stream of it. Rear axle ratio, transmission ratios, etc. are all upstream of the VSS.

 

[7.3 powerstrok]

thanks that was my next question

 

[Dave 001]

Best article I've come accross on the subject.....

http://www.supermotors.net/registry/media/76022