So I picked up this truck today. Its a 1994 F250 460 with 4x4 the engine runs flawlessly and the transmission shifts like I am getting rear ended. I did a fluid change and it helped and I ran a code for 639 and I replaced the VSS on the axle Now I am getting a 452 Code could the folks at the Auto parts store may have given me a bad sensor? or is it my cluster? My speedometer does bounce a bit and it did bounce badly when I hit speeds over 55MPH and I unplugged the RABS module and it did okay when it comes to bouncing. So is it my cluster?

Thanks!

 

A 1994 with a E4OD can not get a code 639 as a 1994 E4OD does not have a OSS/TSS.

Maybe you have a 4R70W transmission and a F150?
The F250/460 only had the E4OD.
The 4R70W dose have an OSS.
If you have a 4R70W/F150 with the smaller engine then it does shift off the OSS and the if the VSS or the PSOM was bad it would still shift OK.
I drove for a week with my PSOM not working at all before changing it out and my 4R70W shifted just fine.
Not sure if the PCM even uses the VSS/PSOM for operating the 4R70W transmission at all.

It does sound like you have a weak signal from the VSS if the speedometer works better with the RABS not plugged in. Clean up the old VSS and put it back in as they very seldom go bad by losing their magnetism and becoming weak. Maybe the gap is too large between the tone ring and the VSS.

Also clear the stored codes in the PCM after fixing the VSS or the 452 will hang in there for 60 startups.

================================================== ===============================================
DTC 639 indicates frequency or voltage of the TSS/OSS is insufficient to the Powertrain Control Module (PCM).
Possible causes:
-- Open circuit in harness.
-- Short circuit in harness.
-- Damaged TSS/OSS.
-- Damaged PCM.

 

Its an F250 with a 460. And I am sorry I didnt get the first code I mentioned. I forgot what it was and I looked in my book and took a stab lol but I do have a 425 code. I took it on a test drive and it worked beautifully I had it out for a few hours driving on the streets and highways. Until I drove to the next town over I had an issue on my way home it was shifting hard again and the cruise control wasnt working.

 

Well shucks a F250 with a 460 in 1996 will not output a 425 code.
Did you mean 452 as in your other post?
When the PSOM quits outputting you will lose the speed control operation and the speedometer will act up or quit.

 

yes sorry 452. The speedometer did jump around a bit last night and it does wave

 

Sounds like maybe bad bearings in the rear end.
It is hard to say without watching the information from the VSS on a scope.
I would dough that the PSOM or the RABS module would cause it on if it works sometime and not at other times.
Do you get the RABS lamp to come on while driving?
With out a good data to the PCM from the PSOM the transmission will shift hard.

Attachment 277289

/

 

Even if it's a rear end issue would it be intermittent like that? I mean it did work fine for several hours. Then it started to act up. I ordered a speedometer on eBay to test it just int case. No I don't get an RABS light

 

It could bad caps on the PSOM board. So if the replacement PSOM from ebay fixes it let us know.

The PSOM:


/

 

I'll let you know man. I traded my 92 f250 for this truck and it went good during the tests and everything of course

 

I am pleased to report shes works fine now with a new PSOM. plugged my ABS unit back in and I Am still getting needle bounce at 55-70 MPH but I just unplugged it and it stopped. I will just get another ABS unit. Thank you for your input