Hello there, im have a problem with my 91 f350 its been shifting weird as in downshifting and shifting up two gears and droping the rps down low it just started doing that today along with the od light blinks but its only everynow and then if i turn my truck off and turn it back on it stops... im just wanting to know what would be the simplest fix without geting a new tranny or rebuliding it.

please help thank you

 

vss or blown fuse. check fuse first.
vss=vehicle speed sensor.

 

check for codes,could also be the MLPS.

 

thank you will check in the morning

 

And to clarify on the VSS coment, the one you need is on the tailshaft housing of the trans (or transfer case if truck is 4x4), and not on the rear axle. There is a VSS on the rear axle, but in '91 it's only used for RABS purposes, it was in '92 when they started running everything and then some off the axle-mount VSS.

That said, hook up a scan tool to the PCM and see what codes you end up with, this may narrow down the problem.

 

Couldn't have said it better myself

 

haha well thank you i asked some shops around here and none of the knew what the heck i was talk about.. never going to those places now just to find a good place to read the codes. thanks again for the help, if you have anymore suggestions i would like to hear those

 

Check for codes and then check the MLPS (Manual lever position sensor) connector for corrosion/wetness. There was an issue on our trucks with this. There was a technical service bulletin in like 95 or so. If you look on the driver's side of the transmission it's the black plastic assembly that the shift linkage connects to. If that doesn't fix it (cleaning or replacement) check the VSS. My vote is MLPS though.

 

Warm up the engine and transmission then pull your own codes: Ford Fuel Injection » How To Run a Self-Test