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Unread 01-09-2014, 06:43 PM   #1
jeepforumrich
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42RE no overdrive

No Overdrive (4th gear).

I have a 1999 Jeep Grand Cherokee Laredo XJ, 4.0L straight six cylinder, 4wheel drive with a Sel-Trac shifter.
Transmission is a 42RE.
Transfer case is a NP242.

Some history about my car:
about 1.5 months ago I replace my PCM because of a stalling problem and that fixed issue.
Then I decided to rebuild transmission because of a 1-2 shift problem when cold. This is because of a seel problem on the drum. Problem was fixed.
I replaced frictions, steels, seels, and filter, 3-4 accumulator spring because was broken. ATF+4 fluid. Rebuilt tranny, overdrive, and valve body.

Then Within the 1st 50 miles of driving after rebuild I got a CEL (check engine light) code P0783 (3-4 shift malfunction).
I did not experiance any driving problems. I cleared the code and it never showed up again.
I took a long trip and 1st 1,000 miles I had overdrive. Around 1,000 miles into the trip while driving 70mph I
experianced a few times the rpm would fluctuate from 2200rpm to 1950rpm and back up again (or it could have been the other way around do not remember).
After stoping for gas and entering highway again I had no overdrive.

I am not getting any new codes since the P0783 code.


These are the things I have done recently in no particular order:

1) Checked fluid, correct level, not burned, no smell, and red.
2) O/D Overdrive light is off all the time even at high rpm. O/D button when pressed shows on dash, and goes off when pressed again.
3) Rebuilt valve body 2nd time.
4) New TPS (throttle position sensor)
5) Shift selector mode switch on transfer case which was bad. This show on dash if in 2 wheel or 4 wheel drive
6) Checked NSS Neutral safety switch. Has backup lights. Tested with Multimeter and appears to be good.
7) Speed sensor on overdrive should be OK because getting mph reading on dash. Cleaned and reinstalled
8) New Overdrive solenoid and TCC (torque converter lockup solenoid). Dropped pan and replaced. The magnet had a small amount of clutch material (mud). There where a few speckles in pan almost not visible at all.
9) New Governor solenoid and Governor pressure sensor. Dropped pan again. There where again very small speckles of alluminum almost not visible in pan. It was alluminum because tested with magnet.
10) I tried different positions for the TV cable (throttle valve cable).
11) Tested governor pressure and it is 1 psi increase for every 1 mph. Starts at 0 psi.
12) Checked all fuses under hood and under drivers side dash.
13) Switched ASR (automatice shutoff relay) relay with transmission power relay
14) Had two transmission shops take a free test drive with snap-on meter. The first shop does not see anything wrong and it appears that the pcm is commanding the overdrive unit to shift. He said he would start with testing the wiring and if nothing
found he would tear down transmission and look for issues there. The second shop says that the transmission is getting the commands
and locking up the torque converter in 3rd gear. He thinks it could be a problem within overdrive unit. So I pulled overdrive unit
and they looked at it and it was good. The clutches where not burned and good.
15) Since I removed overdrive I checked overdrive piston seel. Checked surface of piston for scratches, and also checked if the check ball was still there in piston housing.



Here are some possibilities that I can think of and how would you go about testing them:

a) Wiring harness issue?
b) PCM?
c) Overheating issue because of a stuck check ball in transmission cooler line?
d) Inline fuse or resister somewhere.
e) A mechanical problem inside transmission that prevents overdrive from shifting.

Any thoughts or ideas would be appreciated.
Thanks

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Unread 01-10-2014, 07:36 PM   #2
laybackman
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Isn't there a fuse for the overdrive? could be the switch also. List of possibilities from a FSM.

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Unread 01-10-2014, 08:05 PM   #3
jeepforumrich
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I wish it was as simple as an overdrive fuse but I could not find a fuse for overdrive in engine compartment and under dash drivers side. I did test all fuses and did find a burnt fuse for cigarette lighter which I do not use.

As far as the O/D switch it is always off when I first start car and the only time the light will show "O/D OFF" is if I press button. So would that mean I do not have an issue of the switch and wiring to PCM?

I did have my car hooked to a snapon transmission tester and it would show that the car commands overdrive and goes into 4th gear but it actually does not go into 4th because the rpm's do not drop. The more I press the accelerator the higher the rpm's.

The only other thing on the list that i am guesing could be the problem is lack of pressure at the overdrive piston. I am looking into testing the overdrive pressure on test port but I only have a gauge that goes up to 100psi and I think that port goes past that up to 130psi. But if I do have a problem with pressure the only thing that I can think of that could be causing it is a stuck ball in the overdrive piston retainer. I know the ball is there because I saw it when I removed my overdrive but I should have checked if it is not stuck.

Thanks for the list of causes and solutions
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Unread 01-11-2014, 09:06 AM   #4
jeepforumrich
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Found hydraulic pressure problem, but what is causing it?

I tested the pressure on the overdrive port and I have 0 psi at all times even at full throttle. I though there would be some kind of pressure (5 psi at least)at all times to keep the pump pre-loaded for fast 3-4 shift (3-4 quickfill valve). What could be causing this? I went thru my valve body thoroughly and replaced ALL solenoids and pressure sensors and wire harness. Nothing left to change out inside valve body. When I had overdrive removed I checked the piston, seals, and piston retainer. Also I did see a checkball in the retainer, but I did not check if it moved or not. But if it was stuck should'nt I still have some kind of pressure at the test port even the checkball was stuck open or closed? What else could it be?
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