Finally, after several months I have narrowed an issue withTC Lock-Up / Un-Lock.

Without going into all the details. The TC Unlocks normallywhen operated in overdrive. However, if I use the O/D Button on the Shifter (orany tune with Transmission Shifting), the vehicle almost stalls when coming toa stop (drops to < 500 RPM before recovering to 750 RPM).

The Transmission is crisp, well maintained, Good Line Pressure, Proper Temperature, Stall Speeds are within spec for Converter, and operates as designed otherwise. Does the same without chip installed, no Codes using Snap-On or Autoenguinity.

Transmission Solenoid Pack, PCM Issue, or other?

I can find nothing in any technical manual that addresses this issue (FOMOCO, ALLDATA, ATSG).

Thanks

Tom

 

Mark K will be along to tell you the issue...after you check for codes.

 

I've never seen one do something like this.

 

Coast clutch?

 

Kind of a shot in the dark here but could the O/D switch be faulty causing the circuit to not open and allow the TC to unlock? Or is there a solenoid in the circuit that could be bad?

Idk man like I said its a shot in the dark but it seems really odd to me that it locks and unlocks normally unless you use the O/D button, which sounds like it is causing the TC to be locked up for way to long on deceleration, (or just staying locked all the time for that matter). When the O/D button is on and you slow down (without it stalling) and then go back up to speed does the TC operate or does it just bang through the gears?

 

You might be onto something.

If the coast clutch has a big leak it could cause the torque converter clutch to drift on. In the lower gears the only thing that is different with the OD switch off is that the coast clutch is on. Maybe it's failed. A pressure gauge in the test port will show the line pressure low when the engine speed is dropping if this is the problem.
That sure is a shot in the dark! It does show that you don't know what the O/D switch does. This is impossible.

There is a solenoid that controls the torque converter clutch. It doesn't know if the OD switch is on or off, so I don't see how this could do it.

 

Thanks for your replies.

I just finished a data collection run and reviewed it. The TC, solenoids, slip, and signals, by-pass valve opened at about 100*F, all within spec.

I didn't note low pressure at any time while driving 20 miles or so especially during the braking to a stop process. Performs like a new pump. Although I may have missed it or something glancing at it and traffic at the same time.

A also noted no difference in PCM signaling regardless of what position the switch is in. The voltage wave forms are identical (I/O). I may be focused too much on the switch because I use it for added engine braking when hauling. It may well have the same issue occurring during normal operating conditions but not as noticeable.

Since I've become more aware of when it does it, it seems to do it at operating temperature.

Even though it was serviced 10k miles ago, I'm going to do a service on it and see if there are any improvements in the complaint or metal in the pan. I can always recover the fluid and re use it if I have to go further.

 

Subsribing.. Not my PSD, but my F150 4.6 does the excact same thing. I have been trying different stuff for a long time.. It dives on the RPM just coming to a stop. like the TC won't let go, As Tom described to the letter. operating temp and all.. It has left me dead in intersections or on left or right hand turn on a couple ocasions.

 

Well, I pulled the Pan and both the fluid and inside looks brand spanking new, nice and pink. Cut the spin on filter open and not a sign of anything foreign. Same with the in-pan filter. I did notice it doesn't have the normal "pungent" non-mistakable odor of the Mercon friction modifier though. - Nasty! Absolutely nothing in the pan or on the magnet. Looked brand new. Just wiped it out with a lint free cloth and some Brake Clean - Sparkling. I did notice a scratch in the pan. Hmm, nothing that would be caused by the VB. Possibly when it was serviced.

Removed the solenoid pack and tested it - All's Good

All the pistons move smoothly, no broken springs, etc., put all that back together. So, at least the bottom half doesn't have an issue.

I am waiting on the Filter to come because the local ford dealer doesn't stock it. Said it would be here in an hour; that was two hours ago.

I'm beginning to think this might be Engine related some how.

I'll post back when I get her all together and test drive it.

 

I don't understand this. How did you know that the bypass opened at 100°F? Why would it open? If it opens that indicates a blocked trans cooler.

That was looking at a mechanical gauge installed in the test port on the side of the trans, right?

The ONLY difference when the OD is off is that the coast clutch solenoid is energized. Nothing else changes. When the OD is enabled the coast clutch solenoid is off.

 

I had a Fluke temperature monitor on the Cooler return line on a "T". The temp began rising somewhere when the PCM trans temp was about 100* Maybe I should have said it closed...

I had about 2 qts flow in 20 - 30 seconds on the return line when Hot idling in Park prior to the spin on filter. It was about the same after the filter. So, its definitely flowing well. The time is based on a fat guy with bad arthritis getting up and trying to run around the truck as fast as he could (me).

I had a mechanical Gauge in the test port with a 6' line and had it through the window on the dash in front of me.

I was monitoring the Trans Temp through the PCM (along with the TC Status, Slip, and Active % and so on with the Snap On). None of them exceeded the lo/hi set points I had entered from the Ford Shop Manual.

I just did a complete service. The issue still exists but not as prominent as before (Quicker Recovery - no Stall still drops to about 500 but recovers quicker - about half the time - about a second now). I did every thing I could to get it to >180 but she only got to 170* and I didn't want to beat it any harder. It's 94* here today.

I get the overdrive switch - either on/off switched by ground through the PCM Coat Switch Solenoid. I've got good engine braking and down shifting as well. Hmmm

I will get someone to drive it tomorrow and monitor the line pressure closer as well as the RPM. What's considered an acceptable range for the line pressure during coast engagement / disengagement? I'll start looking for that now. I'll record everything from WOT to Stop and vice versa while doing it.

Found the pressures: 50-65 at idle with brake applied until stopped from 4th with the solenoid ACTIVE (Light Off). 50-75 from 3rd with the solenoid IN-ACTIVE (Light On). So, anything below 50 is BAD.

 

The switch is only connected to the PCM. The switch is a momentary contact. Every time it's pushed the software changes the OD OFF state to either on or off. It does not go through any solenoid.

When the software turns off the overdrive due to reading the switch input, it will then turn on the coast clutch. The switch does not do this directly.

 

Mark,

Got it. Thanks!

Edit - Found the Troubleshooting Matrix in the FOMOCO Shop Manual for the Coast Clutch System Diagnostics. In addition to line pressure it has several other checks for signals and grounds from the PCM dependent on the position of the TCS and TCIL. The easiest is just to drop from 4th to 2nd below 40 MPH ACTIVE and 3rd to 2nd INACTIVE. So, I'll be back pinning a few wires off the PCM and again at the Solenoid Connector. I've now got a much better idea of how the system actually works. And, I've learned O/D isn't O/D, it's a complex system which 4th gear is just one.

I also see where a failing IPR can generate the same concern. I'll monitor that as well.

I'll post back when I'm done tomorrow. On the bright side, next week the wife is having several disks fused and she'll be on drugs and won't be able to take me away from my projects - I'll have plenty of time to pull it and rebuild it if necessary (no use in going half way in to fix the Coast Clutch and do nothing else).

 

I got a little side tracked over the weekend.

Harassed my buddy who works in a Transmission shop until he finally gave in and we did it on his lunch hour today (Only cost me Wendy's). We used his pressure gauge and electronic monitoring device specifically for Transmissions. He had me remove the Chip from the vehicle prior to our testing.

He said everything transmission related seems to be operating "better than expected" with over 200,000 miles. In fact, said it looked more like a low mileage well maintained transmission. I now understand the coast clutch as he explained it to me while he engaging and dis engaging it using the switch, monitor, and drive position selector. There was an issue with snap rings dislodging but he said that was corrected prior to my model year transmission.

It did it only one time with the O/D Light Off. Where I though it was only doing it with the O/D Light on. He immediately looked at the history we were recoding and said the transmission had nothing to do with it. It performed as it was supposed to. Then we (he) looked at the engine monitoring and nothing there looked out of the ordinary. His unit uses a wireless transmitter attached to the pressure port and the pressure never dropped below 55 PSIG. I want one, he said they were only a few thousand dollars... WOW! and his unit pig-tails into the transmission so you can actually see if signals are being sent by the PCM and received by the transmission - Pretty cool.

So, he then looked at the Engine while we drove for about 10 miles and said it looked good too. IPR, IPR DC, ICP, TPS, etc. But, it didn't do it again and he had to get back to work.

The last impression he left me with was a possible failing Pedal Assy out of range which would allow lower the RPMs coasting to a stop, a corrupted flash in the PCM, a chaffed wire or connection causing the intermittent problem with any number of things.

So, where to from here?

Tom

 

I apologize in advance if this is an obvious question, but does it do the bad behavior without the chip? You said your friend had you remove the chip prior to his testing, which implies that you had kept the chip in during all of your previous testing up until that point. He said your trans is great. Have you reinstalled your chip since his tests? In between time, did you experience the behavior you are trying to address without the chip installed?