Hello,

So I was driving my 1995 f150 351w down the highway and all of the sudden the truck's speedometer started spazzing out (by this I mean jumping between 0 and 50.) The ABS light also came on and the truck started jumping with power, the revs would gain like it was in neutral then shift and catch again. I dont know whats going on, my best guess would be the wheel speed sensor.

Any help asap would be much appreciated.

thanks

 

I'd check the speed sensor on the diff first off

 

How do I go about doing that? just replace the sensor on the rear dif?

 

Also if it helps: while I was driving back from college, with this problem occurring again, I noticed the truck would be carrying along at an unknown speed and all of the sudden the revs would jump up as if i had a clutch and proceeded put my foot on it, then a few seconds later released it and the truck jumps then revs drop back to where they were.

 

A quick and cheap option would be to check the interior lights fuse, on my 94 351w it's the #8 in the interior fuse box. I had a similar problem months ago and it turned out the fuse was bad even though it wasn't blown yet. Pulled it, looked ok, put it back in and POP, replaced it, haven't had a problem since.

Probably not your issue just putting it out there in case..


Possible Speedo culprits:
VSS
PSOM
Wiring/Connectors

 

yeah that fuse has been blowing but not to recently. that was my first thought when the problem started

 

Take a look at the wiring going to the speed sensor, I've seen that get damaged by road debris.

You might also want to see if you can figure out what's causing the interior light fuse to blow, there's usually a reason.

-Steve

 

^^This is why your speedo is spazing out^^

 

Yeah, like I had presumed it was the rear speed sensor. Had a hell of a time replacing it. It was falling apart when I was taking it out. The casing for the sensor ended up dropping in to the dif and I had to take it apart to get it out.