4wd OK?

Excuse my ignorance- jeep owner for 3 months

90 MJ I6 Pioneer- I recently got my MJ back from the dealership where it was getting the cps replaced. Prior to the trip, my "part-time" 4wd dash light was functioning. Got it back and went to put it in 4wd high- no light (yes I checked the bulb!). Now today, the midwest gets dumped on and my rear end is all over the place even with 120 lbs of sandbags (could also be my semi-bald tires). ((Can I get 235/75r15 on my MJ???))

How can I test to see if things are working ok- jack all 4 wheels off the ground and do the spin test?

In 4 low (which I believe is always on???), I can not get over about 5 mph in 1st without winding my rpms up. Does that mean 4wd is funtioning properly? Or does 4 low automatically control engine rpms regardless of thw 4 wheels turning?

Thanks!!

It sounds like the dealer might have messed up the vacuum lines going to the motor on your axle that puts the xj in 4wd. Thats what it sounds like to me anyway. Jack your front end up and pull the vac lines from the (axle) motor. Switching from 2wd to 4wd the vac should switch from side to side. Anyway it sounds like its time for a posi-loc. Its not hard to make one for cheep, I put one in my yj. :wave1:

posiloc? tell me more? I have heard of people welding parts together so that the 4wd is always on- is that what you are referring too?

why jump to a posi-lock? we dont even know what the issue is... its best to call the service mamger and tell him the problem... there are a few things they may have messed with while doing the CPS.... though they shouldnt have.. depends on the knowledge level of the tech really.... take it back and have them troubleshoot for free..... are you positive it was working the day it went in the shop? or just assume since they serviced it since the last time? a reputable shop will give a lil extra if treated nicley... it does sound to me like the vacuum lines are the issue though... as far as your top speed in 4lo . thats because you are reducing your final drive ratio to a LOWER GEAR.... rather than jack it up.... geta friend.... find an icy or slippeery snowy spot... put it in 4wd and hit the gas hard a few times with your friend watching from the side... rear spinning and front not? 4low also.. the light may just be unplugged since it is up around the area the CPS is in.... the front axle has a disconnecting mechanism that is vcuum operated.. if the vacuum is the problem it wont operate... the exception to this disconnect would be if your transfer case has 2 4HI positions.. that being a fulltime t/case that does not disconnect.... im thinkin the light is unplugged.... let us know what you come up with....
mike

I am not positive if the 4wd worked prior to the visit to the dealership. I just remember the part-time light coming on the five or so times when I put it in 4wd high.

Do you know where the sensor light is located exactly?

I ran it pretty tough today on wet/icy roads. My rear end would slide a bit, but nothing like if 4wd was not working at all. So I am assuming the light is just disconnected?

Anyone know where the part-time sensor runs into- transaxle or tranny?

Thanks?

Sounds like my XJ...
It takes a while for FT4x4 to kick in and sometimes my light does not come on. Or the PT4x4 light stays on and I don't know if it switches over to FT4x4.
I was told that the linkage within the transfer case needs to be cleaned up for this all to work better.

Also, I was told to ease off the gas and loose the lead foot in this type of weather.

The dash light is operated from vacuum, as is the actual shifting of the axle disconnect.

You will have low range either way if the front wheels are driving or not, so the high rpms is no indicator of 4wd.

There is a vacuum switch on the transfer case output (approx 7/8 hex, with IIRC 4 vac lines exiting it. Also a vac harness that plugs into the axle disconnect motor, on the rear pass-side of the axle shaft. check if both are connected...

sidriptide said:

why jump to a posi-lock?

Click to expand...

I didn't. I said if the vac motor/lines where messed up that he should get a posi loc. Well, thats what I ment anyway.

So what is posi loc???

I am beyond confused- as in- if the 4wd vacuum is broken, I can get a symptom such as posi loc? or posi loc as a solution to the problem???

HELP!!!

a posi-lock is a mechanical device to engage/disengage the front axle.... it was suggested as a possible fix if it turns out that you have major vacuum issues.... not the worst fix but not the toop of the list for troubleshooting... so to clear your head a little just disregard it totally.... it sounds to me like you "think" you have 4WD... as i said before. the best way to figure out if it is really working or not (unless you have a heated garage and plenty of jackstands) is to have a friend stand around while you try spinning your tires on a VERY SLIPPERRY surface.. 2wd..4HI.. 4LO... if your front are not spinning you mostlikely have some vacuum or linkage issues.. if they are spinning its probably just the light or switch...
mike