The Diesel Stop banner

1 - 5 of 5 Posts

·
Registered
Joined
·
69 Posts
Discussion Starter #1
I need to know how the PCM tells the e4od to shift in and out of 4th so I can solder in some kind of diagnostic to make sure the transmission is getting the appropriate signal.

I have a problem no transmission guy I've called thus far (over a dozen) has given me a glimmer of hope on.

Basically, the transmission will sometimes, unpredictably, pop out of 4th and then pop back in. When it pops back in, the TC is still locked. It shifts normally with no noticeable slipping, including into 4th with no jolt. It only jolts when it pops in and out of 4th without my say-so.

Pulling over and waiting, say, 20 minutes seems to make it stop for a while. However, since the problem is random I really can't say for sure. One guy suggested that maybe the TC was getting hot, expanding, and putting pressure on the discs. Another guy said it was probably electrical. Another guy killed and chicken and threw bones on the ground.

I've heard a dozen different possible scenarios with absolutely no guarantees a tranny swap would fix anything.

I want to try to eliminate the wiring as a possible reason for this happening, however I have yet to find any information online on how the PCM tells the tranny to shift into 4th. I was kinda hoping it was just a 12v signal I could wire a dash light to.

This is the only schematic I've seen and it doesn't mention 4th/OD shift. Is it a binary/combo os 1 & 2?

Solenoid PACK.jpg Photo by subford | Photobucket
 

·
Registered
Joined
·
10,656 Posts
Mark Kovalski would be the one who can tell you the gory details. Here are some diagrams for you. Hope this helps. Cheers!
 

Attachments

·
Registered
Joined
·
1,869 Posts

·
Registered
Joined
·
2,374 Posts
Are you sure the tranny is shifting out of 4th on its own, and not doing so based on a control signal from the PCM? Hacking something in to a digital system doesn't sound like a good idea to me; I would start by monitoring live transmission data in via the diagnostic port. There should be a way to watch what gear the PCM is saying the transmission is in, vs. the actual gear it's in.
 
1 - 5 of 5 Posts
Top