I have a 2001 4x4 7.3 ambulance package with a 4r100. I have about 12,000 miles on this rebuild and I just have some of the weirdest issues. I hoping someone can send me down the right road before I have to pull this thing again.

So I'll break this down for everyone. I'll go throw the issues and what I have tested.

1. I randomly get a error code p720 which is the OSS sensor - This has been replaced and the hardness appears to be okay. Things I have noticed, It does this error only when shift from drive to reverse (mind you not all the time, more likely when I have a trailer hooked up) When this error happens or i should said right before it throws the code. My speedometer will jump up to 10mph for a split sec and back down.
2. When reading the TSS with FORScan I also noticed that my TSS would read 0 for a sec while decelerating around the 30mph mark , then around 27 it picks back up. This sensor was replaced with the transmission. I only use OEM sensors.
3. The transmission will flare into 4th gear only if the torque converter locks in 3rd, but not all the time and if I slightly back of before the shift its perfect. I notice that my TC lock up is as fast as I would like it to be.
4. If I have the OD off on the column and I am at a stop sometimes it likes to act like the TC is locked or something and tries to pull me forward but goes away quick and this isn't every time.

Those are my issues in a nut shell. I Just serviced the Bypass line at the 12,000 mile marker, the filter was great still but changed. I changed the fluid and the old fluid was still candy cherry red, with very little on the magnet at the bottom of the pan. The transmission runs about 140F to 165F on hot days and 125F to 150F on cold days.

I did a parked pressure test of the transmission and everything seems within spec. I am leading to it being a electrical problem possible sense It does really show signs of burn up or anything like that. All the gear do shift fine and if I lay into the boost with the TC its does breakaway or anything. I do have a hydra but its doesn't seem to be any different running stock tune.

If you guys need more info I can provide it. I have plenty of data from FORScan and I do know my way around a Transmission. Oh and I changed the VSS as well

Thanks!

 

I had a similar P0720 issue. Turned out the rectifier in the alternator had gone bad and was injecting AC signals into the truck's wiring, which interfered with the OSS signal to the PCM.

 

I read that can be a issue, Does simple unplugging the 2 wire connector from the alternator test this? Or do I have to completely disconnect all the wires from the alternator. On this note I have 2 Alternators and I have unplugged the tops two wire connector but this didn't fix the problem but I did notice a drop in voltage. I do want to test this theory with my second alt but it is hard to reach.

Could a multi-meter with a AC clamp be able to pick this up?

 

I'm not sure. Mine was intermittent so I had to drive for awhile before the issue would manifest itself. Driving for awhile with a partially or fully disconnected alternator was not an option for me.

I'm guessing an oscilloscope would be needed to make a difinitive diagnosis.

 

I will look into a that, I am going to try and disconnect my lower Alt's 2 plug wire and see what happens. otherwise time to track down a oscilloscope.

 

This was a topic in a recent thread but for the life of me I can’t remember which one. Tired a quick search with no luck.
But the person discussing it had dual alts and had both of them act up at different times.
The thread even discussed how to test. But I think disconnecting the small wires was one way to quick check. IIRC he disconnected one and ran like that for a while.

Noob, ringing any bells so we can link him to the thread?

 

Found it! Check this out.

https://www.ford-trucks.com/forums/1...er-issues.html

 

Good job finding that thread @RacinJasonWV . Reps sent!

 

Thanks Noob but you might want to wait and see if it helps him!