Trans downshifting

[hastur]

First the vehicle details:
1999 Explorer 4 dr. XLT 4WD, 4.0 SOHC, 5 speed OD auto (code D?), 158k, no engine or transmission codes, O/D button works.

The problem: At highway speeds (60-65 mph), on cruise or not, the transmission seems to randomly downshift from 5th to 4th, then back up again. There is no connection between load and the downshift. Sometimes downhill, sometimes flat road, sometimes uphill. Sometimes it won't happen on my commute (23 miles with 2 traffic lights), some days it spends as much time in 4th as 5th. The only thing that seems to correlate, is that when I hit a bump in the road it will sometimes downshift. It seems like it wants to be in 5th, but is told to downshift, then times out after 2-10 sec. and goes back to 4th. The O/D off light doesn't come on during these downshifts.

I had it checked out by a local tranny shop who couldn't get the problem to repeat, so they said it was probably a drivability? issue.

My guess is that I have a connector or electrical component going bad, but I don't know where to start looking.

Any thoughts?

Thanks,

Rob

 

[hastur]

Wow, I guess this is a real head scratcher. A little more info.

Coming home tonight I had a chance to observe a little more of what is going on. With the cruise at 65, the tach was showing about 2250 rpm, then it would shift and rise to 2500. I assume this is a shift from 5th to 4th, but when I hit the O/D button it goes to 3000 rpm. Maybe it isn't dropping to 4th, I'm not sure.

Any thoughts?

Thanks,

Rob

 

[my98nnj]

When the gas pedal is released the torque converter unlocks.
Step on it again to accelerate and the RPM's rise for a bit, the converter then locks again and the RPM's go back down. It's not really a shift your seeing.

The cruise will make this happen as the road incline/decline changes. Some people are notorious for not keeping a steady foot on the accelerator, making this happen more often.

When you press the O/D button, it will shift up into 4th gear. That's why you're seeing a bit more increase in RPM's.

Pay a bit more attention to what's really going on and let us know if this is really what's happening.

 

[hastur]

More data:

Coming home tonight the trans acted up 4 times. The trip is about 20 mi., the temp. was about 85, windows partially down, AC off, cruise on 65mph, pretty flat N. Indiana State Rd.


First: Going uphill to get on the highway. I was accelerating mildly and it unlocked for about 3sec. Nothing was really changing except my speed. I was probably going 50-55 when it locked, unlocked, then locked. I was still going up the hill at the same acceleration when this took place.

2nd: I was going down a slight hill, hit an expansion joint and it unlocked for 2-3 sec.

3rd: I was cruising along on a flat piece of ground and it unlocked for 2-3 sec.

4th: Going down a slight hill, it unlocked for 5 sec.

It acted fine when I stopped for a light about halfway through the trip.

I hope this additional information helps.

Thanks,

Rob

 

[shadowless127]

Only one that stands out to me is number 3.

Sounds like your TQ converter is going.

 

[hastur]

Only one that stands out to me is number 3.

Sounds like your TQ converter is going.

Thanks for the direction. I just have a couple of questions.

Could it be the computer telling the TQ to unlock based on bad input due to a faulty sensor or a wiring problem? It does seem to be less common when it's wet outside.

If I don't fix a bad TQ immediately, am I going to ruin anything else?

Thanks,

Rob

 

[drdoom]

If I don't fix a bad TQ immediately, am I going to ruin anything else?

Thanks,

Rob

Absolutely.
Ask me how I know.

 

[hastur]

Absolutely.
Ask me how I know.

OK, How do you know?

 

[drdoom]

OK, How do you know?

My Explorer caught on fire while driving it to the shop to have the codes read (the O/D OFF light was flashing). It was due to a Torque Converter Clutch malfunction.

 

[my98nnj]

More data:

cruise on 65mph,


First: Going uphill to get on the highway. I was accelerating mildly and it unlocked for about 3sec. Nothing was really changing except my speed. I was probably going 50-55 when it locked, unlocked, then locked. I was still going up the hill at the same acceleration when this took place.

Normal for the TC to unlock under acceleration.

2nd: I was going down a slight hill, hit an expansion joint and it unlocked for 2-3 sec.

Down hill, off the gas, TC unlocks. Again, normal.

3rd: I was cruising along on a flat piece of ground and it unlocked for 2-3 sec.

Cruise may have gotten off the gas briefly to control speed. TC Unlocks - normal.

4th: Going down a slight hill, it unlocked for 5 sec.

Down hill again, off the gas, TC unlocks - normal.


I honestly don't think there is anything wrong with your transmission.
Check the TPS, make sure the sweep is clean and linear and it's adjusted correctly.

 

[hastur]

Thanks for the help

A couple of data points:

Going to work this morning, no unlocks while cruising. 20+ mi., 67 deg.
Coming home tonight, two unlocks. Both times on flat ground at 65, after hitting an expansion joint or a snowplowable lane marker.

There is something abnormal going on because it has gone up and down a dozen times, spending 3-5 sec. in each mode on a flat piece of ground with the cruise on.

I'll lookup how to check the TPS and look at that. For what it's worth, I think it's an electrical gremlin that is getting me. I just don't know enough about the electrical system to know where to start looking.

Thanks,

Rob

 

[hastur]

Just to close this thread properly.

I changed the TPS tonight. It was a very easy job, easier than changing the oil. During the test drive, it behaved better than it has in quite a few miles. The shifts are less random and the unlock problem seems to have gone away.

I'll put a few more miles on it this week and see how it behaves.

Thanks for the help.

Rob

P.S. Next, the brakes.