I have a 96 F250 . A couple days ago my speedometer started twitching up and down, then a mile or two down the road the overdrive light started flashing and abs light came on . I got home and Scaned for trouble codes and came up with a p1728 . Has anyone else had this problem ? P.S. I changed VSS sensor in rear axle and problem didn't go away.

 

Check the wiring for the VSS. All of those problems point to the VSS. (Though I don't know what that error code is...)

 

Good luck! Ive been dealing with a VSS code forever now and can not figure it out.. I just had the trans rebuilt and still have this on going problem. Ive even taken it to ford to figure out whats causing the VSS code and they don't know.....

Ive went through sensors, wiring, PSOM, computer.... Cant figure it out...

Im about ready to just throw a 5 speed in it.

 

The code, I think, is excessive torque converter slippage, possibly due to incorrect VSS data.
I would do what Phy suggests and check the condition of the wiring from the VSS on the axle right along the frame rail.
I think I would then pull the rear diff cover and check that the tone ring is not loose or damaged and that diff bearings are good.

 

86F150302,
It could also be the speed control module or the RABS module. You could try unplugging them both, clear the codes, drive it and recheck the codes.
If you still have the code check the AC voltage signal going to the PSOM and the computer.

If the AC voltages are right you may have a bad computer or a bad pin in the computer plug.

If the AC voltages are wrong you may have problems in the rear end like "Lazy K" said above. While in there check the VSS gap.

By the way as for the fuel system and VSS/PSOM the Ford dealers seem to know very little about the Ford trucks before 1995 for the F150 or small F250 and up to 1997 for the larger F250 and bigger. At least this is what the feed back seems to say from posters on this site. They have also got rid of the test equipment for our era of trucks.
All of their training is done on/for the newer trucks and cars.

 

Thanks for the ideas and suggestions ! I'll get to looking this weekend and see if i can find something .

 

I think I'm chasing a broken wire or a bad connection . I looked and moved around the wiring harness to the transmission and to the rear axle , now my problem has mostly gone away . The speedometer still bounces , but not as bad as it first did .

 

I did away with that whole circuit and went to digital speedometer, running off the speed sensor at trany tail shaft. Isin't the V.S.S. at the axle housing just for A.B.S. in these early models ? Also, check ground wires.

 

This thread and the OP are talking about the 1992 and newer trucks that have the PSOM and RABS fed from the rear end VSS/ABS sensor.

Yes the 1991 and older truck use the VSS on the tail shaft of the transmission for the computer and the ABS is fed from the rear end sensor.

 

I had the same problem,plus CC would not stay engaged. I also changed sensor in axle housing to no avail. Real close inspection of wiring (red and green twisted) found a location where someone had pierced the plastic covering when installing inbed 7 way plug. This lead to....CORROSION....which followed the wiring all the way up to PCM. Tried many ways to replace wiring, nothing worked correctly. Sold truck later.

 

Thanks subford for clearing that up.

 

A 5 speed won't fix it, since the speedometer gets its reading from the rear axle. Now if you talking about shifting problems related to the VSS, then yeah a 5 speed would eliminate that problem.

 

By the way, I still have a very slight wavering speedometer when the ABS module is connected. I have had two different PSOMs, 3 different VSS sensors, and 4 different ABS modules, 2 were remanufactured and one was NOS. I just leave the ABS module disconnected.

 

I don't know about the brand new ones, but don't alot of the newer vehicles still use a differential mounted VSS? My friend's 2003 super duty does.

 

Yes shifting problems related to vss code. It's been to Ford, 2 trans shops, and another shop. Can't find what's causing it.