94 7.3 IDI-T, E40D shifting hard??

[SteelRanch]

My transmission recently started shifting hard up through the gears, it also bounces back and forth in and out of overdrive as it upshifts.
I’ve done a ton of research on the issue and gone through almost every aspect of the truck trying to diagnose what’s causing the fault. FYI I am not running LED tail lights

Despite my best efforts I keep getting error code 29 and the problem isn’t going away.

Thing I have done:
- New VSS sensor
- New Tach Sensor
- New FIPL/TPS sensor (correctly adjusted, 1.17v idle and 4.37v WOT)
- Instrument cluster pulled, inspected and terminals greased with dielectric grease.
- Engine harness plugs pulled and greased with dielectric grease

Im not sure what else I can do to try and diagnose this issue, has anybody else experienced this? Any tips or suggestions would be much appreciated.

 

[Nero]

I had the same problem on my in laws truck. The vss is goofy on these. Signal goes to the cluster, then the cluster modifies the signal and sends it to the TCU. Make sure the signal wire from cluster to computer is good.
Do you have a speedo when driving? If yes, that just means speedo gear to cluster is good.

 

[SteelRanch]

Any idea which connector and color wire from the instrument cluster to computer this is?
All gauges and instruments work as per normal so I know the signal from the VSS to the cluster is good.

 

[XOLATEM]

I believe that Nero has you on the right track. I just checked some old tech info from the middle 90's and it confirmed what he advised. I can add a couple of things that may or may not help. When I replaced a VSS mounted on the rear axle I would also replace the connector. it was available as a pigtail then and probably still is. You may want to take it back out and confirm that your tone ring on the rear carrier is ok all the way around...it can split, get damaged, or dislodged and alter your signal.
Another thing that may be more likely that you need to check is the VSS signal in (both + and - ) at the 60 pin connector at the TCM. A wiring diagram with help you on that. This code only sets on a road test so you have to monitor the signal either driving or with the axle supported and wheels free to turn. This is all I have at the moment that may be helpful.

 

[Nero]

I can get you a schematic after work, unless someone else beats me to it

 

[SteelRanch]

Thanks for the tips Nero this will be next weekends project. I have just ordered a chilton manual with all wiring diagrams.

 

[trackspeeder]

My transmission recently started shifting hard up through the gears, it also bounces back and forth in and out of overdrive as it upshifts.
I’ve done a ton of research on the issue and gone through almost every aspect of the truck trying to diagnose what’s causing the fault. FYI I am not running LED tail lights

Despite my best efforts I keep getting error code 29 and the problem isn’t going away.

Thing I have done:
- New VSS sensor
- New Tach Sensor
- New FIPL/TPS sensor (correctly adjusted, 1.17v idle and 4.37v WOT)
- Instrument cluster pulled, inspected and terminals greased with dielectric grease.
- Engine harness plugs pulled and greased with dielectric grease

Im not sure what else I can do to try and diagnose this issue, has anybody else experienced this? Any tips or suggestions would be much appreciated.

PSOM could cause this issue.
Try scanning it for codes again. 29 isn't a fault code. There is a 26 code. That will cause all kinds of weird issues.

 

[SteelRanch]

So I managed to solve the issue here and boy do I feel like a dummy…
this past winter we brought the truck in for some serious work, me and my son had it in bits cleaning and replacing various components, seals, rubber hoses, gaskets, lights etc we did swap out LEDs for the majority of the lights except the tail lights which I knew to leave conventional bulbs in.
Just recently my son bought and fitted a new LED third brake light up on the back of the cab there and forgot to mention to me….

After spending a day pulling and greasing connectors, pulling the instrument cluster, double checking FIPL voltages and throwing tools around the shop after each unsuccessful test drive, i began walking around the truck cursing and spitting considering ZF5 swap options, selling the thing, driving it into the pond and walking away… I looked up and noticed the third brake light which I had paid absolutely no attention to beforehand.
Removed the LED third brake, went for a test drive and problem solved.

 

[Nero]

Always love the easiest fixes.