MPG is easily displayed with an ordinary vaccum gauge, relabled to fit your real-world experience with your particular vehicle. More vaccum, better mileage, less vaccum, worse mileage.

I haven't found a way of easily dissecting the innars of the PSOM processor which is where the mileage is stored, as different vehicles use different chips and some have built in flash as our f-trucks do, and others have external flash chips that apparently store other data as well. If we knew what the processor was, we could google for the chip info (or at least a sister chip that's based on the same thing more or less), then attach to the reflash control pin to enable writing to the flash, then in turn pulse serially to the one processor pin that accepts SPI data.

All the PSOM's I remember seeing have the processor chip blacked out, and I never bothered to scrape under it to see what the processor is. Ford seemingly has a liking for Intel for most things, so it's at least somewhat likely it's based on an intel chip of some kind. The PSOM doesn't really do much, so the processor is likely not to be very sophisticated. All it does is count pulses, use a divider to calculate mileage, shove that into the flash, display that on a 4-bit LCD, and swing a stepper around with a needle stuck on the end.

Anyone who wants to scrape down to the chip numbers, by all means feel free and please post your results. I always worry about scraping too far.

 

Subscribing

 

Frederic,
Do you know if there is any difference between a 1995 Lighting PSOM and a 1995 non Lighting truck PSOM?
I know the head goes to 120 and non to 80 but I am just talking about the PSOM.
I have heard they had an improvement to the PSOMs in 1994 also.
I have also heard that all years are interchangeable also, is this not true?

A PSOM out of a 1995 F-150 non Lighting:
Big Chip:
There is an large i on the left side.
Numbers on chip:
600BFKC008
1992 FORD
L4412026 PSOM
maybe a 1 then 80 8112

Numbers on board:
F3UF-14A608-DA PWD-2256 PSOM LOGIC

 

I have researched some of the numbers on the chips of one of my psom's. I will have to find it again and do it all over.

Frederic, do you still want one of these speedo/psom's to play with? I have a few to play with.

Also. I may have found a way to slow down the speedometer without having to reprogram the psom. If my theory holds true under testing it will help those of us who have a fast speedometer due to putting in one out of a different truck (my truck has a higher gear ratio than the lightning it came out of) and I will post the results. Probably in a new thread. The downside is that while I may be able to slow down the speedometer if it is reading fast, I have not figured out how to speed it up if it is reading slow such as after putting larger tires.

 

To slow down or speed up the speedometer just reprogram the tire size into the PSOM.

 

my truck did the samething 399,999,9 i was wacthing becous i wanted to see it hit 400,000,0

 

That is true. However you only get up to six (?) chances to get it right. What I may have found is a way to do slow it down without having to reprogram the PSOM.

 

I forgot about this!

Now my 95 E350 PSOM is acting up with the leaking capacitor. I though I got all that crud off the PSOM pc board but didn't tranny went to hard shifting and no cruse control. The pcboard is full of acid from the leaking capacitor. Was going to pull and swap out the B37AG ic which looks like a 8 pin I2C eeprom to another psom pc board thats good.


Anybody find more info on the eeprom Ic? its labled
~
~b37ag

I can't find any info on it.

 

I finaly got some info abut the EEPROM that is in the PSOM

Its a Microwire 93Cxx or 93LCxx varient.



I lost all the info about them due to a winblows crash last December. But I did have my notes written down in a notebook!