tranny problems

[huskybdawg]

hello i have a 1991 ford explorer with a A4LD transmission.when i drive downtown it shifts fine but when i go on the highway.doing around 60 miles an hour, its always shifting back and forth on flat ground going at a constant speed in 3rd and 4th gear. i was wondering if anyone could help me, much help appreciated

 

[MrShorty]

Which shift is being effected: 3-4 shift or TCC lockup? Both are electronically controlled. Having it shift back and forth would suggest to me that you have a loose connection between the PCM and the transmission. I would start by pulling codes and looking through the offending circuit.

 

[BrooklynBay]

Welcome to this forum! It's possible that the overdrive band needs to be adjusted. A dried up servo piston will leak, and lose apply pressure on the overdrive band.

 

[versitalbear]

I have the same problem but what is the PCM?

I have this same problem but mine is an 93 explorer and on a flat road it shifts constantly between over drive, drive, and third gear unless I shift to just drive then it onl shifts between drive and third.
Now don't get mad or laugh but I have noticed on here that members will use annagrams for the parts but if you could at least type out the full name of the annagram at least once in your responses for us stupid people that doesn't know that the PCM isn't "Puberty Control ************" you don't need to spell them out every time it is mentioned but you should at least type it out once in your replies, then use the letters from then on.
I know electronics well enough to trace an electrical problem if I knew what the heck the PCM is. I have completely built a onboard computer for a 95 VW Rabbit from scratch so I don't expect you to know what the CPU, CCLK, or the TLIP is in those circuts so please do the same for us who don't know the same about what your talking about.
Thanks for understanding what I am trying to say.

 

[BrooklynBay]

Welcome to this forum! PCM is the powertrain control module or otherwise known as the computer. Only the overdrive, and the torque converter clutch are electric on a 93. Check the vacuum line going to the modulator for leaking transmission fluid.

 

[versitalbear]

Thanks for a start up place

I really hope it is the pcm its self because out of the 6 I have either rebuilt or compleatly built from scratch, they actually seemed to run better and had a marked increase in MPG (miles per gallon), however stupid I am with the abrivations, I am not totally dumb so I know if a vaccum line that connects to something will usually have some sort of diafram and if there is oil in the line it would mean there is a bad diafram in the unit. But what I would need to know is there is only one vaccum line going to the tranny and it connects to something that is bloted to the tranny, would this be the point I would check for the oil in the hose and what is the thing it is connected to called so I don't look like a dork when I go the the parts store and ask for the thingamagig that has a vaccum hose on it bloted to the tranny? The parts store love it when I come in because they know they can sell me a ton of things I really don't need, to fix a problem. thanks.

 

[Gadget X]

The "thingamajig" is called a vacuum modulator or a modulator valve, depending on who you talk to.