My 93 explorer 4x4 with auto tranny shifts in and out of overdrive with steady throttle at hiway speeds. Up to threee or four times per mile. I had it rebuilt three years ago by aamco and I took it in right at the end of the warreny (i got the extended 3 year) and they said that is common but said i need a flush that wasnt on the warrenty. So I paid them for that and now the problem is back but im no longer covered. Any advice on what problem could be, if it requires another rebuild, and if anyone has aamco stories horror stories I would appreciate any info....thanks matt

 

Question, because so many people confuse the two: are we talking 3-4 shift or torque convertor lockup clutch engaging? What you are describing doesn't sound normal to me. Both the 3-4 shift (aka overdrive) and the torque converter clutch (TCC) are electronically controlled by the PCM. The first thing to do is determine if the constant shifting is an electrical fault or a mechanical/hydraulic fault inside the transmission.
Here's how I would proceed:
1) Run EEC-IV self-tests and verify that the computer thinks everything is ok. Because the EEC-IV system controls the 3-4 shift and TCC, any faults in the EEC-IV system could cause the problem you're having. If you need instructions on running the self-tests, see www.dalidesign.com/hbook/eectest.html
2) Get a wiring diagram and identify the TCC and 3-4 shift control circuits. Inspect these circuits and make sure they are intact (You will need an ohmmeter to check the solenoids because they are inside the transmission). Inspecting these circuits includes the power supply from the EEC relay. Repair any broken wires/loose connections and see if this fixes the problem.
3) If the circuit seems intact, perform output state test (refer to above EEC-IV self-test article) while monitoring voltage drop across the solenoid in question. If you can see the PCM switching the solenoids, then you've verified that the PCM "can" shift the transmission.
4) Perform road test while monitoring voltage drop across solenoid in question. Should be able to see electrical "switches" each time the transmission shifts into/out of 4th.
That's a good start.

 

Hey, thank u so much for the detailed response. I believe it is the torque converter lockup clutch. I do not have the equipment nor experiance to try the tests you suggested but the tranny goes thru all four gears then once in overdrive(4th right) it does the shifting. I manualy shifted to D or (3rd right) and the rpms jumped way higher than the tranny jumps when it shifts on its own. When at hi way speeds, say 65, my rpms are about 2100-2200 and when it shifts unnessasarily it jumps to about 2400-2600. it does not feel as drastic as the manualy downshift to third so I believe it is the torque converter lockup clutch. I also think this is what the guy at aamco said the common change was due to. I really appreciate the time you took to respond and would like to hear what you know about this problem and if it requires an internal rebuild? My name is matt and thanks again.

 

Agreed, it does sound like the TCC clutch. The only conditions in which I would expect that kind of behavior is either on an uphill climb (throttle near wide open), going downhill (throttle nearly closed), or slower speeds (35-45 mph). Under these conditions the PCM may be changing it's mind whether or not to engage the TCC. Under steady throttle, flat ground, above 55 mph, the PCM shouldn't be "undecided" about the TCC clutch engagement.
Aamco should be able to diagnose this, unless they are trying to avoid the engine management side of the issue. If Aamco won't deal with it, then find someone else.
Maybe nows a good time to obtain some of the necessary experience/equipment to figure this out yourself. Equipment needed = wiring diagram + low end digital multimeter.
Whether or not it requires internal transmission works depends on whether or not the problem is inside the transmission or not. My gut feel is that the problem is electronic in the EEC-IV controls. From there it depends on if it's external to the transmission (wiring or computer control) or internal to the transmission (wiring or control solenoid). As an example, this could easily be caused by a fault in the throttle position sensor circuit.

 

Thank you again for the response. One more thing if its ok? I commute 70 miles to work in my explorer and this changing happends about 60% of the time. Back and forth up to 3 times a mile. Is this damaging my tranny further or is it ok to drive till the weekend when i get paid and can have it looked at? I know it is hard to diagnose an explorer online but just an opinion on whether I can crive to work this week would be greatly appreciated. Thanks again....Matt

 

It should be ok. However, if you want to be sure, unplug the connector for the TCC solenoid/3-4th shift solenoid at the transmission. You'll lose 4th gear, but you will eliminate any possibility of damaging the transmission/torque converter.

 

Hey thanks again for all the great advice. Last week I drove it to work three days and the tranny never once unneccisarily shifted at hiway speeds with steady throttle control on a even grade. I did not do anything to repair this problem but it seems to have gone away....Have u ever heard of this happening...should i not get to excited... well whatever happend thanks again and I feel better prepared to face trannsmission repair shops because I have a little better understanding of the auto tranny...is it true it is the most complicated part on a vehicle? Anyhow...take care ok...Matt

 

I had this problem with my 93 sport and it turned out to be a Throttle Position Sensor, 30 bucks and 5 minutes later I never had the problem again!