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Overdrive shifting

H

horatio4a

NAXJA Forum User
Location
Nature Coast, FL
Hello. '97 Cherokee 4.0/NP242. 250,700 miles. Only problem...overdrive. Doesn't always go into OD. When it doesn't, I stop, shut it down, wait 15-20 seconds, restart, reverse a short distance and go. Then then OD works for a day or a month at random, no rhyme or reason. Also, when I am towing with a load, it shifts every time. The above "method" of the temporary "fix" was discovered by mistake, out of frustration.
Fluid full and clean, changed every 50,000.
When OD engages, it's solid.
Help. Any ideas? I hope it's not the torque converter.
My hope is that someone else has had this problem and can point me in the right direction.
Is there a pressure valve on the side of the transmission that could be bad?
Thank you.
 
The overdrive is controlled by a few inputs thru the PCM/TCM so a good scanner should point you in the right direction.
 
Is the Throttle Valve cable properly adjusted ? Is the Throttle Position Sensor a genuine Jeep part ? Cheap Chinese clone parts can cause strange problems. Are you using Dexron-III/Mercon trans fluid ? Some Cherokee owners report shifting issues that are solved by using the specified fluid.
 
Not familiar with the year but I assume this is AW4? If so its solenoid controlled by the TCU. Attach a voltmeter to the line feeding the overdrive solenoid so you can monitor it while driving. See if the TCU energizes the solenoid but it doesn't shift into OD.



If it does then probably the solenoid, if it doesn't then the TCU most like isn't getting the correct inputs shut as from the TPS or the TCU may just be bad.






Steve
 
By "OverDrive", I assume you're referring to the torque converter locking up and not 4th gear. That final couple hundred rpm drop once you're done accelerating. Brake lights aren't stuck on right (one of the inputs that tells the computer to unlock the t/c)? If you have a meter, test the TPS and and the solenoid resistances. Assuming it's shifting normal, at the appropriate times based on rpm/throttle, its not sluggish when it does decide to shift, then I'm going to guess the t/c solenoid needs replaced. It's about $70 for the set of all three new AW4 solenoids off Amazon.

Reference thread for testing the solenoids.
https://www.naxja.org/forum/showthread.php?t=1137433

There are lots of threads on replacing the solenoids if you do. Big things are: you don't really need to replace the filter; don't overtorque the pan screws, they're 7-ftlbs only; dex/mercon only.
 
Thank everyone for the quick replies. They helped.
Turned out to be two things.

1.) pulling up on the brake pedal got me OD sometimes when driving. Adjusted the brake light switch at the top of the brake pedal arm got it to work. That would probably explain why going over large bumps or rough RR crossings made it go into/out of OD randomly. But...that wasn't the end of it. Still would "fall out" of OD on occasion.

2.) I read a thread where a XJ owner ratcheted his tranny shifter through its detents multiple times when not running to troubleshoot the Neutral Safety Switch. Damn if that wasn't a problem also. No OD? Stop, run the shifter roughly through the detents and OD is good. Am now going to follow another thread to remove and clean the internals of the switch.

NAXJA is great. Obviously, I am not as experienced as many of you, but your knowledge sent me in the right direction for troubleshooting. I hope I can return the favor.

Thank you.
 
horatio4a said:
Thank everyone for the quick replies. They helped.
Turned out to be two things.

1.) pulling up on the brake pedal got me OD sometimes when driving. Adjusted the brake light switch at the top of the brake pedal arm got it to work. That would probably explain why going over large bumps or rough RR crossings made it go into/out of OD randomly. But...that wasn't the end of it. Still would "fall out" of OD on occasion.

2.) I read a thread where a XJ owner ratcheted his tranny shifter through its detents multiple times when not running to troubleshoot the Neutral Safety Switch. Damn if that wasn't a problem also. No OD? Stop, run the shifter roughly through the detents and OD is good. Am now going to follow another thread to remove and clean the internals of the switch.

NAXJA is great. Obviously, I am not as experienced as many of you, but your knowledge sent me in the right direction for troubleshooting. I hope I can return the favor.

Thank you.
Click to expand...

Ah! The brake light switch would have interfered with the cruise too if you had that. Dirty or misadjusted NSS could mean you didn't have backup lights sometimes. Careful getting it off as the backside is plastic and you don't want to pry too much. Bleeping Jeep has some good videos.

https://bleepinjeep.com/?s=NSS
https://bleepinjeep.com/video/how-to-remove-your-nss/
https://bleepinjeep.com/video/how-to-fix-your-nss-neutral-safety-switch/
 
I would strongly suggest adjusting the NSS before you risk breaking it.
 
RCP Phx said:
The overdrive is controlled by a few inputs thru the PCM/TCM so a good scanner should point you in the right direction.
Click to expand...
Indded, I would underscore the "good" part. My cheap-ass man store (HF) scanner kept accusing the torque converter solenoid. However, after a s'load of labor, I dropped by O'Reilly's AP, they scanned the codes, and came up with four issues -- one of which was the output shaft speed sensor. I fished around in my spare parts bucket, changed the OSSS, and all was good, nay, very good.

Not saying that the OSSS is or isn't your issue, but I learned the hard way that a cheap scanner is not good -- in the same way that a bad sheriff is worse than no sheriff.
 
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