Transmission switching constantly from OD to D at interstate speed

[scsr_11]

Hello,
93 Eddie Bauer Explorer
4x4 Automatic trans
4.0 v6
4 door


Here's my issue I'm needing some direction on. I got on the interstate for the 1st time yesterday and at cruising speed (65mph) the tranny would go from D to OD, D to OD, D to OD, until I either sped on up or slowed down. It wasn't slipping, it was just shifting from D to OD if I maintained speed.

Anyone ever seen this??

(The only thing I've noticed when city driving is that my transmission seems to hold 2nd gear a little long when normal driving.)

 

[MrShorty]

1st thing I'd probably do would be to determine if the problem is with the 3-4 shift or the torque converter lockup clutch or both.

2nd thing, in my mind, since both of these are electronically controlled on your A4LD, would be to determine if the fault is electrical or something else. Could be a loose connection between the PCM and the transmission, or maybe the PCM is actually commanding it to shift in and out at which point we determine why the PCM is doing so.

 

[scsr_11]

I'm a fairly capable shade tree mech (motor swaps, T5 rebuilds, clutch installs), how do I determine the above mentioned possibilities?

thanks,
Josh

 

[MrShorty]

3-4 shift and TCC lockup circuits are pretty basic DC circuits (with the PCM acting as a ground side on/off switch). Get a wiring diagram and a voltmeter and get set up to measure the voltage drop across the solenoid in question. Then you can use the output state test (see my notes on pulling EEC-IV codes) to look for faults in the circuits and loose connections. You could also test drive it and watch for the PCM to change the solenoid's state. If the shifts coincide with the PCM's commands, then you would determine why the PCM is commanding the shifts. If the shifts are independent of the PCM's command, then you would need to look inside the transmission/valve body for the problem.

 

[scsr_11]

bump... Anyone seen these symptoms??

 

[Jack Flash]

I had a similar problem with my 92 Ex. Riding down the interstate at about 65 mph, it downshifted. I was startled and began to try to figure out what was going on.

Happened to look at the temp guage and it showed HOT !...As I slowed down to exit, the temp went back to normal and the thing shifted back into OD. It did this 3 or 4 times on my trip...everytime the temp shot up, the tranny shifted out of OD.

Turned out I was low on coolant....damned heater core was leaking...replaced the heater core & for my peace of mind, replaced the thermostat, too.

It hasn't had the downshifting problem in about 4K miles, so I assume it was fixed....

,
,

J...don't even know if overheating & downshifting were related...but...

 

[scsr_11]

Funny thing you mentioned heater core b/c mine was clogged and I blew it out with the water hose the day b/f this transmission thing happened. I filled the radiator with only water (b/c I didn't wanna waste the antifreeze b/f I could tell if my heater core issues were fixed.)

On the interstate, my temp was fine, but it could have been a little low and the computer knew this and started shifting funny? Maybe the computer could tell there was no antifreeze in the system???

 

[MrShorty]

J...don't even know if overheating & downshifting were related...but...

my temp was fine, but it could have been a little low and the computer knew this and started shifting funny?

I don't know the specifics of the algorithms, but the PCM does consider engine temp (from the ECT) in it's decision to lock the TCC and to shift up into 4th gear. It would have to be very cold or very hot to decide not be in 4th gear. If the temperature on the dash gauge appeared ok, then it probably isn't that, unless the ECT is sending a bad signal to the PCM (ECT is different from dash gauge sender).

ECT is a basic thermistor and would be easy to test with an ohmmeter.