Confusing tranny behavior

[92LXAZ]

In the last week I’ve had 3 different transmission behaviors that I need opinions on.

First a week or so ago my wife was taking my son to school and had to gun it a little bit pulling out of our neighborhood to beat some traffic. She didn’t quite know how to explain what happened but basically it downshifted hard at one point during accel and lurched both of them forward pretty hard. I explained it away as is with the 80 the tranny has to reach a certain temp so thought it got confused by the quick acceleration and said ‘nope’ better down shift. Not sure if 100s are this way as well. However…

The next two I was driving. This instance I had to hit the brakes hard and slow down fast and it seemed it went from 5th gear to 1st instantaneously and because of this even made us lurch forward slightly. RPMs dropped immediately, felt it was going to die but did not. Drove fine rest of the way.

The last one just happened yesterday. Started to accelerate, not crazy hard, right at about 3rd gear it stopped going. RPMs dropped, almost like no fuel but again it stayed running. I pulled over quickly to see if any other symptoms came up and there were none. No CEL. Again drove fine the rest of the way.

Is my tranny going bad? All instances are different, two accelerating with each a different behavior and the third on decel. Thanks for any insight.

 

[AimCOtaco]

I'm no A/T expert by any measure but first thought is the torque converter is not unlocking when it should be. I think you can disconnect the lockup solenoid so it doesn't lock up in the first place as a possible troubleshooting step.

 

[92LXAZ]

Thanks for that @AimCOtaco I'll keep researching.

 

[Eicca]

Check your transmission fluid level and condition. If it's more brown than red it needs to be changed.

Also make sure your charging system is putting out the right voltage, 13.5v at idle and 14+ at rpm. Computers do wonky things when the voltage is too low. Some shop monkey left the negative terminal on my Lexus loose and my transmission was all sorts of funky until I tightened it back down.

 

[92LXAZ]

Well @Eicca might have nailed it. Battery is 12.4 sitting, 13.1 at idle. Both on low side. Battery is the X2 Power 27F, about 1 1/2 years old. Run ARB fridge off it a few times/yr plus Az heat. Time for a recharge or replace?

 

[Eicca]

Swap in a known good battery first, before spending the dough. Those numbers sound decently ok to me but worth investigating further.

 

[AimCOtaco]

13.1 at idle should be plenty for the electronics but it couldn't hurt to try another to rule it out. I wouldn't run out and buy a battery but as a secondary consideration you may want to circle back around and see about boosting up the alternator voltage but only after watching voltage under lots of different conditions.

Low fluid was a great tip as well is the level OK?

 

[RootMeanSqr]

12.4V sounds normal for battery resting voltage for a ~75% charged AGM battery. If voltage at idle is only 13.1V, that's likely either alternator or bad connections somewhere. Alternator may be fine and putting out 14V, but a bad connection somewhere like a ground between engine and battery negative terminal could be causing you to read a lower voltage at the battery. Could also mean that the battery is not being fully charged/maintained by the alternator. Lots of places will test your charging system for free to test alternator output and charge retention of your battery. I would definitely do that before jumping right into another battery. A new battery would initially look like problem is fixed, until it drains down and not maintained by alternator. My X2Power 27F sat right around 12.4V too. That was with my 100k old alternator. Just replaced it this weekend though, will have to see where resting voltage is now.

 

[Julian Stead]

Check your engine ground by doing a voltage drop test, this is the best way as you are putting the circuit underload.

Isolate the engine so that it doesn't start, remove the efi fuse or something. Put as much load on the battery as you can, as in turn all lights on, heated screen and crank the engine. When the engine is cranking over you check the voltage between the battery negative and the engine(something metal). It should read around 0.1v or less for such a big short lead if good, if it is over 0.2v then investigate further as in clean the ground connections, retest and if no improvement then renew the cable. You repeat this for the chassis ground, so move the cable from the engine to inner wing. You can also check the positive cable on the alternator to the positive side of the battery but I am not sure if you can access the cable on the alternator when it is in place.

Max voltage drop is 0.5v but I would clean the ground points if over 0.2v as there should be hardly any voltage drop.