Dried out connection, works in humid locations but not in dry areas?

[scotts90ranger]

Ok, this is for my '97 F350 with 350K miles on the clock... or thereabouts as this is about the speedometer not working...

This system works by reading the reluctor wheel on the rear diff, it's all electric and programmable with the right button sequences (but you only get a certain number of chances from what I've read... it's only reading about 5% fast so I'm not screwing with it).

Anyway, I've had the truck for around 5 years, around 4 years ago was the first time the speedo quit on me, it just gets intermittent, sometimes will work til about 35mph then nothing above that, sometimes flaps full scale (IE goes from zero to max flapping...), speedo and odometer when it gets confused are zero so I have to drive off the tach... It quit on me again this april when I spent 4 days in the high desert in Oregon, went to the Oregon coast to play in the sand where it was overcast over the weekend and the speedo started working on the way home...

I've heard of dry climates being tough on electrical connections, what's the fix? The connection at the back of the speedometer is the issue which is a non sealed 8 pin connector. I spent 20 minutes trying to get the pins out a few weeks ago unsuccessfully, I'll give it another shot if taking it apart and tightening the contacts a little will help, but if just spraying some contact cleaner or something will work better and adding dielectric grease or something will work I'm open to suggestions...

I tell ya, when you have two fuel tanks, no speedo, no odometer, and the bigger of the two tanks doesn't have a working fuel gauge and you are towing in a mountain pass it's somewhat nerve racking...

Thanks for any help! Sorry for being long winded...

 

[RonD]

The speedo and odo share the one "speed pulse" signal
And if you don't get ABS light when speedo stops working then VSS on rear axle is OK

And if no P0500 code "loss of VSS pulse" then computers speed pulse is still working

1992 to 1996 and 1997 F350 used the same PSOM(Programmable Speedometer/Odometer Module)
Located in the instrument cluster
It gets the raw 20,000PPM(pulse per mile) from VSS, shared with ABS module, and converts it to 8,000PPM for use by speedo/odo, computer and cruise control.

Some info here: https://www.ford-trucks.com/forums/1501269-vss-wiring-psom-rab-finding-a-solution.html

Google: 1997 ford PSOM wiring

This module is the most likely part to be effected by temp or humidity

 

[scotts90ranger]

Thanks Ron, it's been a while since I've looked into this... about 4 years ago it did the same thing, took the speedo out to look at, didn't see anything, put it back in and it started working again, then stopped again in April... It has to be a connection issue at the cluster or the rear diff (I'm guessing cluster, but haven't checked the VSS in 4 years...). Reading some of those posts the PSOM is fine since the miles are still there just no speedo/odo readings from the VSS.

I don't have a RABS light on that I know of, but this thing has been hacked over the years... that and it's got a very random set of options, it's an XLT with no airbags, diesel, crew cab, long bed, cloth seats, leather steering wheel, cruise control, power doors/windows, manual trans and transfer case... I honestly haven't looked for RABS components though I'm sure they're there, I know there isn't 4 wheel ABS, no sensors on the front wheels and no pump under the hood.

It's supposed to cool down, so maybe I'll get to spend some time under the thing...