91 Overdrive Not Working

[T-Money]

I have a 1991 Ford Explorer and i just recently got this car. I started driving it on the highway and noticed right away that at 60 mph the tach was at 2600 rpm...well dumb me i was in regular drive NOT overdrive. so at the stop light i shifted right and started driving again. well at 60 mph i was still pulling 2600 rpm. I noticed that on the speedometer at 55 the mark was red. so i figured maybe i have to shift into over drive there...well i started got up to 55 in drive then shifted into overdrive. i felt the transmission shift but nothing happened. the tach stayed steady over 2000 rpm

 

[rhauf]

i have no idea what you're saying.

you do realize you can shift between all forward gears while the vehicle is moving, right? on that note, how about you drive down the freeway at say, 65miles/hour, then shift it into overdrive and see if there is any change. it should drop down at least 100 rpm if the torque convter isn't locked, then eventually it will drop down some more (or it might do it all at once)

cruse at 65 in overdrive should be somewhere around 2,000 rpm.
the red mark at 55 means absolutely nothing. this was something stupid which auto makers did back in the '80s and early '90s when the speed limit on the freeway everywhere was 55.

 

[T-Money]

yea i tried shifting while in motion and nothing happened. i tried at 55 and i tried at 65 and even at 75 mph and nothing happened. the rpms stayed the same no matter if i was in drive or overdrive.

 

[MrShorty]

3-4 shift is electronically controlled by the PCM. The first thing I'd do is look there. Pull codes to see if there are any codes that would be useful. Then get a wiring diagram and a voltmeter and inspect the 3-4 shift solenoid circuit (it's a pretty basic DC circuit, so it shouldn't be too difficult).

 

[FIND]

Also, peer into the valve body diary and transmission rebuild diary, in the transmission/transaxle sections. Those will give you a lot of ideas of where problem areas are so you can determine what else to check and how far you want to get into it.

 

[1Byounkin]

I'm having the same problem on my 91 not going into OD. I pulled codes today and got the 22 code. Which is the BAP sensor (aka MAP sensor). After talking to a member on this site it might be it but I don't know yet until I change the sensor. Only some of the 91s used the BAP sensor all the ones after quit using the BAP sensor. And does your TCC lockup? Just tap the backs going highway speed to see a change in rpms. I not saying that this will fix it because I haven't tried yet. But ya check your koeo codes.
I'm in the same boat.

Does your 91 have the BAP/MAP sensor on the firewall?

 

[T-Money]

TCC? i'm a little slow with exact terms. I'm having an issue with the rear antilock locking up my rear passenger tire.

 

[1Byounkin]

TCC refers to the torque converter. Did you fix you OD problem on your 91, T-Money? I don't know about your antilock locking.

 

[MrShorty]

TCC stands for Torque Converter (lockup) Clutch. At speeds above about 40 mph and in 3rd or 4th gear, it locks up to get a more efficient mechanical connection between the engine and transmission. It is also controlled by a solenoid similar to the 3-4 shift solenoid. Sometimes if you have neither 4th gear nor TCC lockup, you can focus your diagnosis on things those two have in common (such as the common power supply to the solenoids).

 

[tac0meat]

I think speeds vary depending on axle ratios and what not. When my OD worked, the 3-4 shift happened at 45mph, and torque converter locked at 55mph. With that said, no matter the difference in shift points, you should feel 4 distinct "shifts", 1-2, 2-3, 3-4, then TC lockup (which will feel like another shift). Like Mr. Shorty said, if you are missing both the 3-4 shift and TC lockup, your issue might be electrical and easier to address w/o dropping the valve body.

when the TC is locked up at highway speeds, slightly increasing the throttle will not cause a large jump in engine RPM, as the engine is directly coupled to the drive wheels at a fixed ratio. If driving at 65, you lighty increase the throttle and your engine RPM jump up by a few hundred, your TC is most likely not locked/locking.