Quote Originally Posted by 1project2many View Post
Often, complex and challenging symptoms trace back to very simple issues caused by an oversight or two during reassembly. It's possible that a visual inspection could reveal the problem without spending time in diagnosis. A thorough visual inspection can reveal pinched wires, disconnected wires, connectors plugged into wrong places, damaged terminals or wires. A thorough visual inspection should never be skipped or rushed.


You should work to narrow the possibilities. Determining whether or not the problem is in the transmission can be very helpful.

Does your adx show calculated gear ratio?
Have you validated commanded shift solenoid state against the transmission gear?
See P. 48 of https://gear-report.com/wp-content/u...leshooting.pdf
1st gear should show solenoid 1 (or A) "On" and solenoid 2 (or B) "Off." Any other combination should not result in 1st gear. If the PCM is commanding the correct gear and the transmission is not responding appropriately then you may not need to chase the lack of speed data in your transmission adx.


Disconnecting the large connector at the transmission will force the transmission into 2nd gear. Removing power to the transmission will force the transmission into 2nd gear. If you cannot force the transmission into second gear by removing power from the solenoids then you have a problem inside the transmission. Conversely, if you remove power and the transmission remains in the same gear that it was in before you removed power, it would be very wise IMO to confirm (again, if necessary) the transmission is not actually in 2nd gear.


That's a good question. Check to see where the two files are getting data from by opening up the adx for editing. Solving this issue may not resolve the shifting issue but it could help you resolve this question so you can move to the next step.


So what has changed in the vehicle configuration between those logs and present day? Was anything changed in the calibration?


This seems unnecessary. If you could simplify this system it would reduce some unknowns now and in the future.


This is another area where a good visual inspection could be very important. And it's an area where it's challenging to see. I believe that it would be beneficial to see if the pcm is commanding 2nd gear. That is likely the fastest and least invasive test you can perform.
Thanks much. I've spent hours visually inspecting, both before the diagnostics and after. That was the first thing I did - should have mentioned that. I've looked at the harness in back of and on top of engine, harness at the trans and up firewall, under the dash, and at T-case. Next step here will be taking off the TB, brackets for MAP, and maybe even dist and coil - just so I can get a better look at the harness back there.

Calculated gear ratio: an export of the log file to Excel shows two "ratio" columns. In the log I'm looking at, both columns are populated with "4" all the way down.
Trans solenoids: the log files shows A as ON and B as OFF all the way down. Doesn't seems like the PCM is commanding a different gear?
Unplugging the trans connector: I didn't get a chance to do any physical work on the truck today. I will try this tomorrow. Very curious to see if it will go into 2nd.

Vehicle speed in two different ADX files: this is the confusing part to me. Once we start talking about addresses on the chip, I'm out of my element. Trans ADX export has two vehicle speed columns: one is called vehicle speed, the other is "MPH". MPH has appropriate data in it, whereas vehicle speed is zero all the way down. Engine ADX has just one vehicle speed column, with data populated. All three seem to refer to different addresses (packet offset?) by looking at those items in the ADX editor. I also did an export of the log from before tear down (mentioned previously) that used the same trans ADX. In this one BOTH speed columns show data, but the weird thing is they don't match. At low speeds they differ by a few mph, and high speeds (40 mph and above) they differ by 10 or more.

What changed in the calibration from before tear down to now? Nothing. I parked it for tear down, trans working fine. No changes to the .bin after that point.

Parallel DRAC and VSSB. I agree this is unnecessary. I thought it was necessary at the time based on various posts on this site and due to the oddities of my 1991 V2500, but another member here (@Tayto) pointed out to me I could just use the new VSSB to run the speedo. But I was already mostly done with the conversion so I stuck with both. I think eliminating the old DRAC (and extra twisted pair from T-case VSS) will be my next step here. Based on my data analysis described above, it really does seem like the PCM is not getting a vehicle speed value it uses to determine shift points.

Thanks again for walking me through some stuff.