I had some more time to mess around with my truck. The 4r100 shifts great until the truck warms up. After about 10 to 15 minutes of driving it starts. With the gear selector in D and under acceleration it will shift at about 2k rpm's and will be in third gear by 25mph. If I climb to higher speeds it will only shift out of O/D when I get my foot into it. It will not downshift into any gears until I am almost completely stopped. It will downshift and hold gears great if I use the column to shift. I'm stumped. No CEL or flashing O/D light.

Things I have checked:
TPS
VSS
All connections to the transmission
Set tune back to stock
Transmission fluid & level

Will the transmission still store codes even if the O/D light has never flashed? Would you know Mark?

 

It's still a good idea to check for codes. It may have only flashed for a short time and you didn't notice.

You also will probably need to monitor data and see what's going wrong. Something is probably sending bad info to the PCM causing it to shift wrong.

 

I'll try and get the transmission codes read this week as a first step then. Thanks Mark.

 

I had a transmission shop run the codes and found nothing. Now they didn't do a drive test while scanning the truck either. I didn't have time before I had to be back to work. Would a drive test reveal anything more if it didn't show up previously?

 

I've been busy with the move and new job but I think it's time to stop being lazy and figure this out.
Could this be a symptom of a bad or sticky modulator valve in the accumulator body? My theory is once the trans gets to temp it starts to stick and causes the no downshift issue. Still no flashing O/D light or trans codes.

 

The modulator valve only determines how hard/soft the shift is. It can't prevent the shift. It also can't make it upshift too soon.

To diagnose this either remove the valve body and check for stuck valves, or get a scan tool that can look at live data. Somewhere there is bad data that is causing the computer to tell the trans to shift at the wrong time. I expect it is in the vehicle speed data, but that's just a guess.

 

Thanks for the fast reply and information Mark. I'll see if I can find someone here that can check the live data.

 

I haven't found someone that can do live data for the transmission yet. I know my SCT has data logging but I'm not sure how to work it or if it has the capabilities to show me that.

I took it out for another drive yesterday and it started acting up again so I unplugged the alternator and it was still doing it. One thing I did notice that I didn't before is that when it acts up my it will idle at about 1100 rpm's and drop slightly from time to time.

 

If you haven't already remove the tune and put it back to stock and see what happens..

 

The SCT won't tell you anything about the transmission info, I've used my SCT numerous times data logging and it's not great at all. There are laptop programs out there that are almost as good as Ford dealer software I'm buying one very soon

Sent from my iPhone using IB AutoGroup

 

I have put it back to stock and still the same results.

 

What program are you looking at? I may invest in something like that soon.

 

Another question. Like I said earlier when having the problem my idle goes to around 1100 in Park/neutral. Could a problem in the valve body or modulator affect the idle in park/neutral?

 

The valve body can't cause that.

 

Okay. Thanks for the reply Mark. I didn't think so but wanted to make sure before I pulled it apart.