AW4 shifting hard

[Felipe Tiago]

Hello guys,

I have a weird problem and doing the search I found nothing similar...

My jeep is a 1998, AW4 and NP231 with 80,000 miles on it. The tansmission has been shifting really darn hard, I mean hard enough to piss me off.

The case: I start the car, step on the gas and it moves as it should, then when the RPMs reach more then 4,000 it shits from 1st to 2nd really hard and in the normal RPMs but just a bit less hard from 2nd to 3rd. For the rest of the ride it randomly shifts hard but sure it happens sometimes. The strange thing is that if I stop the jeep, turn off the engine and start it again the problem disappears and it shifts perfectly for the rest of the time.

That is, I start the car and it shifts hard sometimes during that ride but will or won't shift hard in the next time I start it, its random.

The problem is random during the day (every time a start the jeep I don't know what to expect) but always happens in the first ride of the day...

What I've already done:

- adjusted the TV clabe (tried different positions for this since it clicks twice or more, it kinda sticks);
- new TPS (I tested this new one and voltage varies smoothly but at WOT the output is only 3.8 volts);
- tested the solenoids: all around 14 ohms in the TCM harnnes and in the plug near the firewall in engine bay;
- cleaned the ground connectors G102 and G100;
- a shop changed the transmission fluid and filter (level is ok and there were no metal particles in the old fluid neither in the pan);
- the last try was having the valve body cleaned (the shop didn't charge me for this because they said it didn't solve the problem, which I thought weird... they also said there were visible issue with the valve body).


So, what do you guys think that could change in the transmission when I turn off the car and start it again to make the problem go away?

Sorry for the long post!

 

[Ou2mame]

Intermittent pressure problem? I don't know... What do you mean there was visual issue with the valve body?

Sent from my HTC M9 using Tapatalk

 

[garr]

Did the shop put Dex3 fluid in or did they use the "SO CALLED COMPATIBLE" ATF4 that Chrysler says is OK?
The AW4 likes Regular old DEX3.

 

[Tim_MN]

The TCM will re-set when you shut off/start the engine. You may want to look into a good used TCM, around here they are very inexpensive.

The AW4 likes Regular old DEX3.

Use Dexron-III/Mercon. Most shops screw this up.

 

[Felipe Tiago]

Intermittent pressure problem? I don't know... What do you mean there was visual issue with the valve body?

Sent from my HTC M9 using Tapatalk

I mean NO visible issue with the valve body, sorry..

I thought the problem could be pressure related (altough now I see Tim_MN has a good point, about the TCM)... and what would cause an intermittent pressure problem like this? the oil pump?

Did the shop put Dex3 fluid in or did they use the "SO CALLED COMPATIBLE" ATF4 that Chrysler says is OK?
The AW4 likes Regular old DEX3.

The shop wanted to put Dexron VI and I had a hard time convincing them to put III but they ended up doing what I said: Dexron III!

The TCM will re-set when you shut off/start the engine. You may want to look into a good used TCM, around here they are very inexpensive.



Use Dexron-III/Mercon. Most shops screw this up.

hmm, good to know that, so it makes sense the TCM might be the culprit..

Used TCMs are not so cheap here in Brazil but I think it worth a shot, I will try this.

 

[Ou2mame]

I almost bought an xj that had a problem with the tcm and it was shifting funny and it ended up being either the ground strap or ground terminal being bad, but I ended up passing on it anyways because it had other issues. I would check all the grounds first because I've seen the wires an inch into the shielding corroded and broken making poor or no connections.

Sent from my HTC M9 using Tapatalk

 

[R.DesJardin]

The TCM does not control line pressure, only the TV cable does. If it's shifting at too high rpm then look to the control system.

 

[Felipe Tiago]

I almost bought an xj that had a problem with the tcm and it was shifting funny and it ended up being either the ground strap or ground terminal being bad, but I ended up passing on it anyways because it had other issues. I would check all the grounds first because I've seen the wires an inch into the shielding corroded and broken making poor or no connections.

Sent from my HTC M9 using Tapatalk

Since this is easier I will check/clean the other grounds tomorrow morning to see if it helps...

The TCM does not control line pressure, only the TV cable does. If it's shifting at too high rpm then look to the control system.

It shits at high RPMs only in the first time it shits from 1st to 2nd when I just started the jeep. The other times I feel like it delays the shifting and then BANG, the gear engages! But like a said, if I turn it off on on again everything may be right, that's the weird part that made me believe it could be something electrical, or the oil pump changing its behavior for some reason I don't know why (if possible).

 

[Ecomike]

Sounds like an electrical/electronic problem. Have you checked the TCU fuse and also tried pulling it and driving it in just manual mode? Might check the VSS sensor as well.

But it could be a valve body problem with sticking valves. Might try some Trans-X additive while looking for ground or other wire issues. Or a bad TPS issue.

 

[Felipe Tiago]

Sounds like an electrical/electronic problem. Have you checked the TCU fuse and also tried pulling it and driving it in just manual mode? Might check the VSS sensor as well.

But it could be a valve body problem with sticking valves. Might try some Trans-X additive while looking for ground or other wire issues. Or a bad TPS issue.

VSS is also new (changed it weeks ago) and I drove with the TCM unplugged and apparently it shifts fine manually. The problem is that the hardest shift is from 1st to 2nd and without the TCM I can't get the tranny to make this shifts, right? When I shift from the 1-2 position to 3 it shifts kinda "firm" only if the RPMs are lower then 2,000 (I wouldn't say it is a hard shift), otherwise it shitfs perfectly.

 

[Ecomike]

In manual mode you must be over 4000 rpm, maybe even 4500 to get from 1 to 2 in the 1-2 manual mode location.

Sounds like it is OK hydraulically, leaving just electrical, so that leaves wires, TPS sensor to the ECU and from the ECU to the TCU, and those units themselves and the first two of the solenoid shift valves that control the gear selection.

Is the TPS an OEM or durajunk sensor?

 

[Felipe Tiago]

In manual mode you must be over 4000 rpm, maybe even 4500 to get from 1 to 2 in the 1-2 manual mode location.

Sounds like it is OK hydraulically, leaving just electrical, so that leaves wires, TPS sensor to the ECU and from the ECU to the TCU, and those units themselves and the first two of the solenoid shift valves that control the gear selection.

Is the TPS an OEM or durajunk sensor?

The TPS is Standard and I testet its output which gave me 0.95 volts at idle and 3.80 at WOT.

The solenoids were all in the 14 ohms range (TCU connector and also in the connector which goes straight to the tranny)

To test the TPS signal from ECU to TCU I can test pin cavs 16-17 in the TCU connector? Ignition on and engine not running? what should I expect?

 

[Ecomike]

That only tests the TPS at idle and WOT, it does not test the TPS for flat spot ranges or noisy operation in between the two. There have been many complaints about bad after market TPS sensors causing issues. I don't have the AW4 manual or factory FSM handy to answer the other question.

Solenoids can work one minute and not the next, be sensitive to temperature (same for a TPS) or stick from trash in the valve....

A ground that comes and goes with engine movement has been reported as a cause for this too. It is near the transmission IIRC. I am no expert on the later XJs, mine are all pre 1991, but most of the AW4 is basically the same in all the XJs.

No way to test the TCU to ECU chat line, it is digital, but you could disconnect both ends and run an ohm test on the wire, but I seriously doubt that is your issue.

Is there a bulkhead connector on the wire harness to the AW4 on yours? if so have you cleaned it? Mine had a bent pin that gave me headaches for years.

 

[R.DesJardin]

It's not the ecm system. I shift mine 100% manually no TCU and so does my son in law, no matter how you rev it it never shifts extra hard. It's a hydraulic issue, something sticking or maybe a broken spring inside.

 

[Felipe Tiago]

Sorry, I forgot to mention that the TPS had no flat spots in my test too.

Regarding the solenoids, I will test them more times, i.e., in the morning before going out with the jeep and after it is warmed up. I will also look for that ground near the tramission.

I intend to do all possible tests in sensors, ground and wiring to rule them out as a cause of the problem before buying a new (used) TCU.. I will make more tests cosidering the suggestions you guys gave me and then I report back.

 

[Felipe Tiago]

It's not the ecm system. I shift mine 100% manually no TCU and so does my son in law, no matter how you rev it it never shifts extra hard. It's a hydraulic issue, something sticking or maybe a broken spring inside.

Well, the results of my manual tests were a bit confusing to me, I didn't know if it was not shifting a bit hard or if a was trying to fool myself... but I really thik it was a bit harder indeed, although not nearly as hard as it is with the TCU plugged in.

I will unplug it and drive for a couple days to be sure and to test it in all the possible conditions (cold, warn, hill up and down).

Someone told me it's normal to shift hard when in 4low, mine does that too. Besides, the hard shiftings I'm reporting in this topic are like the ones that happen when in 4low to me (if it is normal to shift hard in 4low, then you guys can have an idea how mine shifts when in 2wd, cause sometimes it is the same).

 

[Felipe Tiago]

Well, I won't need a couple more days of testing... I unplugged the TCM to shift manually and this time it shifted really freaking hard.

It's not the ecm system. I shift mine 100% manually no TCU and so does my son in law, no matter how you rev it it never shifts extra hard. It's a hydraulic issue, something sticking or maybe a broken spring inside.

You were right...

what about now, is it sure my problem is inside the valve body (or the valve body itself) or something in the rest of the transmission might also be responsible for this?

 

[garr]

My bet is still on the fluid, I would purchase a few gallons of Dex3 & do 3-4 poor mans flushes, driving a few miles between changes.

 

[Felipe Tiago]

My bet is still on the fluid, I would purchase a few gallons of Dex3 & do 3-4 poor mans flushes, driving a few miles between changes.

In my situation it worths a shot. Besides, I think I can't trust that shop when they say they put dex 3, since the guy really tried to convince me that dex 6 would be better...

 

[Ecomike]

My bet is still on the fluid, I would purchase a few gallons of Dex3 & do 3-4 poor mans flushes, driving a few miles between changes.

I agree, and don't forget to add about 1/2 pint of Trans-X (if you can find it?) with each transfusion to help clean out and dissolve any varnish that may be making the valves stick. I have been using it for 40 years and avoided hard part repairs about 18 times across about 10 rigs thanks to it. Walmart has the gallon jugs of Dex III here for about $12.50/gal here. Not sure about Brazil?