OK, so what does the thing then do when I do the following: Key off, press and hold the "Reset" button (the one that resets your trip odometer) and then key on. The speedometer goes to 80 mph+ and then back to 0 and in the digital odometer window "E 08 6" appears. If I press the button again some word shows up. When I had codes on the Truck (Autozone scanner pulled them at the time) the same codes that scanner pulled could be read there. See my Sig for my Truck, maybe some more guys can go out to the driveway and try it. Takes 1 minute and maybe we will figure this out.
That sounds like PSOM.
I dug this out of some archives I have.
The "PSOM" is the (electronic) Programmable Speedometer/Odometer Module, which is on '92-97 only F-Series & Broncos. Earlier ones use a cable-driven (mechanical) speedo which is calibrated by changing the plastic gears in the transfer case tailhousing (or transmission tailhousing on 2WD). The E-series and Aerostars also used the PSOM for short periods, but I don't know the ranges. Resetting it is EASY: the PSOM uses the "conversion constant" to calculate the vehicle speed from the sensor frequency. You can see yours by holding the Reset button while turning the key forward to Run, then release Reset. The needle will do a full sweep test, and the odometer display will show "E ## #", meaning English units, the microprocessor revision (mine is 08), and the conversion constant lockout count (maximum is 6). Canadian ones might show "o" in the first position meaning "Overseas" (Metric) units. Pressing Reset again shows "###CAL", which is the conversion constant (without a decimal). 31x10.50's should be 9.18 .
If you want to change the constant, find the single-wire connector under the glovebox and ground the LightBlue/Yellow wire before turning the key on (you still have to hold the Reset, as before). Everything is the same as before, except "CAL" will flash, indicating that the constant can now be changed. Press the Select button to decrease the constant by 0.01, each time. When the constant reaches 5.00, it goes back to 11.00 . Larger tires or fewer teeth on the tone ring require a lower constant - R&P changes have no effect. When you have the constant you want, press the Reset button to lock it in. THIS WILL DECREASE THE LOCKOUT COUNT BY 1 - WHEN IT REACHES 0, NO FURTHER CHANGES CAN BE MADE.
To abort the changes and maintain the lockout count, turn the key off before pressing Reset. When finished, turn the key off and disconnect the LB/Y wire from ground. The "PSOM Programming Enable" circuit (the LB/Y wire under the dash) is only used when you want to change the constant and use one of the lockouts. You can check the constant without grounding that wire.
Here is a partial list of constants and revs/mile for certain tire sizes:
When the lockout count reaches 0, it doesn't self-destruct; you just can't change it again. It keeps using that constant forever. If you want to change again, you have to buy a new PSOM. But, remember: the only reason to change it is for a tire size change. After 6, you ought to have the size you like!
I think the reason a) it's not publicized, and b) there IS a lockout count, is so that people don't set it so the odometer registers fewer miles until they take it in for warranty work - they'd use up the 6 changes in 3 trips, and the techs would see the lockout going down, and void the rest of the mileage warranties. But that's just a guess.
The E4OD is the only one that uses the PSOM signal (I think), and it's connected to the OUTPUT, so it would be reading the converted speed. But it's fed directly from the PSOM to the EEC even on vehicles with mechanical automatics and manual transmissions, and I don't know why. My truck ran fine after the engine swap, but before I added the ABS rear end and PSOM, so I don't think it's used on trucks without the E4OD.
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