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Discussion Starter #1
Hi I'm new here, this is my first post, and I was hoping someone could shed some light on my problem...

Yesterday I was on the interstate doing about 70 and my OD was slipping ( I think). The RPMs would fluctuate slightly, and it kept going in and out of gear into 3rd on hills (more than normal). Then it just kicked back HARD into 3rd and wouldn't go into overdrive again. I had a slight trans. leak but didn't realize the severity of it and it turns out I was pretty low on trans. fluid. I added 2 quarts and it filled it to the proper maximum. It still won't go into overdrive so my question is did I ruin my overdrive? I have heard that it will automatically disengage overdrive if fluid gets too low, would it be possible that I just need to reset something electrical?

This is a 94' ZJ V8 with 260,000 miles, and I just acquired it recently so I don't know about any maintenance it's had. The only thing I did do was add some Lucas oil automatic trans. treatment the first time I topped off the trans. fluid and it shifted like a dream after that. 1st, 2nd, and 3rd still shift great. Also I don't know if this is the proper section to post this, just know it's not intentional.

Thanks
 

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Discussion Starter #2
I'm going to drop the pan and change the filter and fluid next time I get the chance and see what that does.
 

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260K is a lot for anything. you are on the correct track by doing the filter and fluid. make sure you get the CORRECT FLUID. i used the napa synthetic stuff. it was $50 for a case, and the computers at autozone are wrong in that it says only 4 quarts for a service, you will need way more (i did). i ended up using about 7 quarts when i did my fluid and filter change, and 13 quarts when i did the full reubild.
as far as the not shifting in to O/D, wiggle the button on the dash. if the light is ON then you will NOT have 4th/OD. now, be very clear, does the torque converter lockup when its not shifting in to 4th? if so, then the converter and bands are fine, and i'll bet that the button is messed up in some way.

Good Luck,
Hunter
 

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Discussion Starter #4
Torque Converter Lockup

I'm not sure exactly how to tell when it is. All I can say for sure is that I tack over 3k on the interstate and if I let off the gas at all it slows down faster since it's in 3rd. It makes no attempt at all at shifting into OD, if that helps. The button also seems to be functioning, I can turn it off or on and the light works so I would think the switch would.
 

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You might try removing the brake light switch, disassemble it and give it a good cleaning. The contacts in there disengage the OD. Be sure to adjust it correctly.. there should be some clearance when the brake pedal is pressed. Just a thought
 

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/\ thats good info, but he said 4th gear, not the actual clutch for the lockup... the brake light switch does nothing for the "gears" but has to do with the lockup control of the torque converter...
however, if the button is messed up, and is not allowing to shift in to 4th, AND his brake light switch were both bad, then yes, all his problems are solved. 2 switches going out at the same time, unlikely, but it is a Jeep; nothings impossible. check the plug on the trans that controls 4th gear. it is the only computer controlled thing (aside from rev lts, TCC, and NSS) and may have come off completely or maybe loose. then check the plug on the PCM and make sureit doesnt have any broken or loose wires where it comes out and goes behind the motor. have you recently changed the cap, cam sensor, oil psi sender, or spark plugs? if so, maybe you damaged a few wires that are in that harness.
 

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Use ONLY ATF+4 fluid. Nothing else in that tranny.

Don't put any more Lucas in it... Jeep says 'no additives'.

What does the fluid look/smell like?

Agree, check the switches first.

BTW, that's the 46RH tranny, the strongest they put in a ZJ. Good tranny.
 

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Discussion Starter #8
/\ check the plug on the trans that controls 4th gear. it is the only computer controlled thing (aside from rev lts, TCC, and NSS) and may have come off completely or maybe loose. then check the plug on the PCM and make sureit doesnt have any broken or loose wires where it comes out and goes behind the motor. have you recently changed the cap, cam sensor, oil psi sender, or spark plugs? if so, maybe you damaged a few wires that are in that harness.
I haven't done any of that mentioned work to it recently, but I will check those wires when I drop the pan and change fluid. I'm sure the state of the fluid in the pan will narrow the problem down pretty good. Thanks for all the help everyone, I just haven't had the time to work on it lately (maybe this weekend).
 

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Use ONLY ATF+4 fluid. Nothing else in that tranny.

Don't put any more Lucas in it... Jeep says 'no additives'.

Agree, check the switches first.

BTW, that's the 46RH tranny, the strongest they put in a ZJ. Good tranny.
agree with everything above... lucas masks problems, not to mention its overpriced and in mopars does way more harm than good. i dont use any of those products but i heard amsoil is better?

x2 on the condition of the fluid and pan. expect to see shavings, thats normal, but if you've got a layer of what looks like penny candy wrappers, its prob time for a rebuild...

Good Luck,
Hunter
 

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Discussion Starter #10
Flush done

Use ONLY ATF+4 fluid. Nothing else in that tranny.

Don't put any more Lucas in it... Jeep says 'no additives'.

What does the fluid look/smell like?

Agree, check the switches first.

BTW, that's the 46RH tranny, the strongest they put in a ZJ. Good tranny.
well I had it flushed by a guy for $120, just didn't have the time lately and wanted it done completely (not just the pan). He just told me it was done and said the old fluid was burnt with a good amount of metal shavings. I'm going to go pick it up in a couple hours and post how it goes.
 

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Discussion Starter #12
Test Drive

now, be very clear, does the torque converter lockup when its not shifting in to 4th? if so, then the converter and bands are fine, and i'll bet that the button is messed up in some way.

Good Luck,
Hunter
Well I just took it for a couple test drives, though it isn't really the best day here (just got a foot of snow). It seems it runs much smoother now. The OD still wasn't working, I tried messing with the button and still wouldn't. All other gears shift great though, and I'm not exactly sure how to tell but I believe the torque converter is now properly "locking up", it seems the rpm's are slightly lower. I'm going to call around and take it to get the computer checked for any codes soon, I am hoping it just has to be re-set or something like that for my OD to come back. As I said it seems to run much better now with the exception of OD not working.

Also, is it possible if the OD was fried in my tranny to just rebuild that part of it? As I've said every other gear works and shifts flawlessly. Sorry if that sounds stupid, but I honestly still don't know how overdrive works and what would need to be replaced for it. Even if this is possible I would probably elect for a complete rebuild anyway, just curious.

Thanks everyone for the help, I will keep everyone posted.
 

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the od unit is separate from the trans... you can just rebuild it, BUT, any debris that the O/D unit shed, is gonna be all through out the rest of the trans. sounds bad, but i would risk the rest of a trans that they only made 3 years of to just guessing that there isnt any debris in it.. you get what i mean?? for reference, on stock tires, 3rd gear, torque converter locked up/engaged 65 MPH should be exactly 3-3100 RPMs. if the converter isnt locking, then it will be (3rd gear) 65MPH about 3500 RPMs... 4th gear TQ locked up will be a little above 2K at 65MPH. 4th gear no lockup would be about 2300rpm
 

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Discussion Starter #14
Overdrive Rebuild

the od unit is separate from the trans... you can just rebuild it, BUT, any debris that the O/D unit shed, is gonna be all through out the rest of the trans. sounds bad, but i would risk the rest of a trans that they only made 3 years of to just guessing that there isnt any debris in it.. you get what i mean?? for reference, on stock tires, 3rd gear, torque converter locked up/engaged 65 MPH should be exactly 3-3100 RPMs. if the converter isnt locking, then it will be (3rd gear) 65MPH about 3500 RPMs... 4th gear TQ locked up will be a little above 2K at 65MPH. 4th gear no lockup would be about 2300rpm
That's really some great news, if re-setting the computer doesn't work then roughly how much would I be looking at for re-building the overdrive? It is definitely about 3k rpms too, so that's a good sign.
 

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Discussion Starter #15
I think I found the Problem!

Got some great news. Tonight I was driving the jeep back to where I store it, and was messing with the OD switch some more out of desperation. I turned it off and noticed the light was on in the DIMMEST bit. Turned my rear defroster on and off (same type of switch, right next to the OD one) and noticed the light goes completely black when it turns off, AND the relay clicks like the horn, etc. When I switch the OD on or off the relay doesn't click! I'm pretty ecstatic about this and plan on working on it very soon, does this sound about right to you guys? I know a few of you made reference to the switch, but the light still goes on and off and just stays on very dimly when I turn it "off". Thanks a lot for everyone's help and I'll let you know the results when I try and fix the switch.
 

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i hate doing this to ya, but i just checked mine, and it stays on pretty dim, too.. but your prev post still leads me to believe it's the switch, or DEF electrical. for it to just not go in to 4th, but shift smooth and fine 1st thru drive fine is just wierd. you didnt by chance change your PCM or mess with it did you?? the PCM controls the 4th gear. change the button in the dash, and then the PCM with different units and report back. btw, those are both waaaayy easier and cheaper than a rebuild. believe it or not, the PCM is easier to change than the switch POD in the dash.

Good Luck,
Hunter
 

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Discussion Starter #17
Electrical

i hate doing this to ya, but i just checked mine, and it stays on pretty dim, too.. but your prev post still leads me to believe it's the switch, or DEF electrical. for it to just not go in to 4th, but shift smooth and fine 1st thru drive fine is just wierd. you didnt by chance change your PCM or mess with it did you?? the PCM controls the 4th gear. change the button in the dash, and then the PCM with different units and report back. btw, those are both waaaayy easier and cheaper than a rebuild. believe it or not, the PCM is easier to change than the switch POD in the dash.

Good Luck,
Hunter
Ah oh well, still though wouldn't I hear the relay click for the OD button when I press it? Do you think by chance when the fluid got too low the PCM disabled it (OD) and after it was filled back up properly it just has to be re-set? This was one of my original theories, and no I haven't ever messed with the PCM. I wanted to take it somewhere to pull the codes, but the check engine light is not on, don't think I've mentioned that yet. And I don't doubt you on costs there, hearing that it's likely something electrical is a monumental relief.
 

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Discussion Starter #18
PCM part purchase

i hate doing this to ya, but i just checked mine, and it stays on pretty dim, too.. but your prev post still leads me to believe it's the switch, or DEF electrical. for it to just not go in to 4th, but shift smooth and fine 1st thru drive fine is just wierd. you didnt by chance change your PCM or mess with it did you?? the PCM controls the 4th gear. change the button in the dash, and then the PCM with different units and report back. btw, those are both waaaayy easier and cheaper than a rebuild. believe it or not, the PCM is easier to change than the switch POD in the dash.

Good Luck,
Hunter
Was just looking on ebay, not a bad price at all. My only question is should I just get a used part like this:
http://cgi.ebay.com/ebaymotors/1994-94-JEEP-GRAND-CHEROKEE-5-2L-COMPUTER-PCM-56028112-/350431248777?pt=Motors_Car_Truck_Parts_Accessories&hash=item5197548189
Or should I go the extra mile for about $70 more and get a rebuilt one with my vehicle's info. like this one:
http://cgi.ebay.com/ebaymotors/JEEP-GRAND-CHEROKEE-Computer-ECM-PCM-ECU-Replacement-/370418779656?pt=Motors_Car_Truck_Parts_Accessories&fits=Make:Jeep|Model:Grand+Cherokee|Year:1994&hash=item563eae0608
Second one also comes with a lifetime warranty, the other is a 30-day (so I could probably test that one and return it if I have the same issues, but I'd rather not, kind of a hassle). I don't mind spending the extra I just want to make sure it's justified first. Thanks.
 

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please do NOT spend that much money on a PCM esp since it could still be the switch POD.... how bout this, im going to my local junkyard in a couple days, i'll grab one for ya, (i'll see about a switch pod, too but you have to tell me is yours a 93-95 or 96-98) pay for shipping and try it, if it works, keep it, if it doesnt send it back and we've eliminated the PCM as being the problem.. sound good to you??

edit 1: there is no relay for the O/D circuit (there may be a fuse, hmm check the one labled TCM in the under hood fuse center, never thought of that till now) and pressing the button just sends a pulse to the PCM that you dont want 4th

edit 2: the PCM learns rather quickly, almost instantly that the prob is corrected (the ONLY exception is O2 sensors and thats any car) so resetting it prob wont do anything but it will NOT hurt anything if you try it... being that it is free and the only thing you lose are radio presets and the time on the VIC, i'd disconnect it and leave it disco'd overnight. take off both leads if you can, do not touch them together, tho...
 

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New to the forum

Hi guys, I'm new to this forum. I just bought a 95 G/C and I'm having similar problems. When its cold am about 60 degrees outside, it never shifts into O/D but at lunch time it works fine. I can tell as soon as I give it gas if I will have 4th gear. Weird but it acts like its slipping as if its trying to raise the RPM"s to pull a trailer or boat. Is there a way to by pass the O/D problem by just keeping 4th engauged? Any input from anyone would be great. I didn't mean to jump in here but I think he is having the same problem. Thanks guys!!!!!
 
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