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Are these symptoms due a bad AW4 transmission solenoid?

bpatto10

NAXJA Forum User
Location
knoxville, tn
Fellow XJ owners,

My 1996 stock XJ, 4WD, AW4 will intermittently (maybe once of twice a month) exhibit this symptom. If I am on the highway the rpms will suddenly increase like it has downshifted out of overdrive. If I then pull over and restart the engine, everything goes back to normal. Alternatively, if I am at an intersection in town (usually after the above happens), when I try to pull away the response is very sluggish and I have to press the pedal down hard to get acceleration. It feels very similar to when you are driving a manual tranny, and try to pull away in a higher gear other than first.

Is this a symptom of one or more sticking solenoids in the AW4?

I had the torque convertor replaced about six months ago due to the classic whining sound, so I don't think that it is the problem. I am leaning toward something electrical, especially since if I turn off the engine and restart everything is fine until the next random occurrence.

Thanks in advance.
 
Have you made sure the cable is adjusted properly?
 
Yes, I adjust it at least once a year. I think this is something electrical in nature, i.e. solenoids, transmission computer, grounds need cleaning, etc.
 
In 4th gear, neither shift solenoid is engaged. It's unlikely a bad solenoid would cause an unexpected downshift from 4th. A bad solenoid not engaging would however cause it to try starting in 4th gear from a stop. Checkout the throttle position sensor as they do eventually wear out and are often the culprit in odd shifting.
 
The first symptom you describe sounds line the torque converter is unlocking. So take a look at your brake light switch as well.

Sent from my SM-G892A using Tapatalk
 
Have you checked your fluid level?

How long since you drained and replaced the fluids? The reason I ask is that I had a problem where the fluid had accumulated moisture. If I drove it for a while and got it hot, the fluid would foam and the pump would cavitate causing a loss of pump pressure.
 
No solution as of yet. I have been concentrating money and time on my rear differential.

It has been occurring less frequently. I performed step 10 as recommended by cruiser54 since it is an easy maintenance item. The downshifting at highway speed has not occurred in several months, so I am keeping my fingers crossed on that one.

Fluids are good, as they were completed changed out with the torque converter.

I am going to order a Mopar TPS switch and new brake switch since they are not very expensive. Both are very good recommendations.

One other item not mentioned is the transmission computer. When I had the torque convertor replaced at a very honest and reputable tranny shop, I mentioned this random problem to the owner. He recommended ordering a new transmission computer from the dealer (not very expensive according to him), as he had seen a lot of oddball jeep AW4 problems caused by just the age of the computers electrical components. He mentioned is that if they are in a damp environment, the insides will corrode and cause random issues. That got my attention as I previously fixed the very common problem with water leaking in through the blower fan on the passenger side.

It occurs so infrequently, that I will almost forgot about it, and then bam it will occur out again out of the blue again.

I wish I had a definite answer for you, but I would try cruiser54 suggestion first, as it only entails the cost of a can of contact cleaner.
 
It's pretty rare for the transmission computer to go bad. Typically an electrical problem would be corroded connections, a bad TPS, or failing solenoids. The board inside the trans computer is coated to protect it from moisture.
 
Possible solution from OP: Neutral Safety Switch

I replaced my neutral safety switch several months ago due to no backup lights and I have yet to experience any of these symptoms. I was going to clean my old one (original part), but after finding a new one on ebay for $42 shipped, I just replaced it.

My suspicion is that the contacts in the old part were getting worn enough to cause these problems.
 
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