My friend had a 93 that done that. It turned out to be a bad connection on the battery post.... whod of thunk

 

I had the same problem with mine and even after I replaced the sensor Istill had the same problem, sometimes the speedo wouldn't work at all. i had to rewire the whole deal from the diff to the speedo. Later I found that I had a short where the wires from the sensor join up with the rest of the wires at the rear of the truck.

 

Never been able to confirm or deny this but I think all PSOM's are the same from 1992-1996.

Here is a link to your PSOM wiring and a photo of a PSOM.
http://i54.photobucket.com/albums/g9...BroncoPSOM.gif
http://i54.photobucket.com/albums/g9...M/DSC02313.jpg

 

would the PSOM cause any noise and/or vibration? My speedo has started jumping around at higher speeds....I'm at a loss as to what has caused it.

 

No Idea, but im sure someone knows.

 

Do a search for "bad psom"

the PSOM stands for Programable Speedometer/Odometer Module. It is the head unit in the dashboard.

They are common to go bad on these trucks, suppositly in 95/96 they were revised and were better.

When they go...they cause fluctations...often when driving at 65 will push way ahead to 85-90...sometimes setting off the speed limiter....and sometimes cause dead spots where the engine will want to die at 2-3 mph (it tells the computer you're going 180 mph and sets the speed limiter for that one spot and the computer shuts off the injectors).

It could also be a bad wire or connection, as the signal is a pulse signal that can more easily be interupted.

It could also be a rear axle issue...either a bearing going bad and allowing the carrier to move...or a bad tone ring...or junk on the VSS sensor...or a number of things (like too much runout on the carrier/ring gear).

The VSS is on the top of the rear diff and also acts as the ABS sensor, I believe it is the same on the broncos with the exception that the broncos also have sensors for the front wheels for 4w-abs.

Any other speedometer head will work, they separate in the gauge cluster when you take it apart.

Don't let the dashboard sit face down (there is a sticker on it telling you not to, why...I have no idea).

They can also be re-programmed for mileage by a dealer...and make sure that any one you get still has flashes left for calibrating it to your tire size (see the tech article for more info on that).

Hope that helps.

 

Many thanks. Should I just goto a Ford dealer for this? Or are you speaking of auxilliary companies like DashUSA? If I just give them my original gears/tire size vs. new tires/gears will that fix the calibration? Because I am certainly off in that department.

I'd like to nip this in the bud pronto!

Again...Thanks for your input

 

You can change the tire calibration yourself by following the directions in the tech article on this website (check the tech articles section, link above).

The dealer can re-program mileage.


Years ago I had a 95 that the speedo went out on and I purchased a new one from a dealer that they re-programmed the mileage and tire calibration for me.

 

Sweet! I just reprogrammed the PSOM, and it worked great. Many thanks !

Tested it on a 10 mile speedometer check station, and for the first time in a long while I hit it right on the money. My shift points have been changed now...not sure if I like that yet....

I took out the VSS..it was a little dirty and there was some metallic dust buildup (very minimal in comparison to some pictures I've seen). I cleaned it up and slapped it back in.

The vibration appears to have subsided, to a point. It's not nearly as drastic, but its certainly still there. Speedometer still wiggles a bit coasting from 70 mph to 60, but I have to look hard to see it.

Hopefully I can get the rest of the humming/vibration nailed down shortly!!

Thanks again for the help!

 

Did anyone figure this out, my 93 5.0 is doing the exact same thing

 

I reprogrammed my PSOM to new tire size. Upgraded to a CV driveshaft and shimmed my rear end to improve the pinion angle. Problem completely subsided.

My issue was only apparent after a 4" lift in the rear.

 

Check driveline angles if it's got a lifted/modified suspension.