2001 Challenger Auto will not engage 4WD

[hybrid]

Hi all,
I recently bought a 2001 challenger and took it out to the country for the first time on the weekend. They got rain (which is great, they really needed it) and I was looking forward to giving the challenger a workout. Very muddy dirt road, shifted to 4WD and no light came on. Ended up getting stuck at a very bad part of the road. The front diff does not seem to engage in either 4H or 4L, but low range itself seems to be working.

I removed the solenoids and they both seem to be working. However, both seem to be powered on with the ignition, whether in 4WD or not. Is this normal? The yellow vacuum line is sucking no matter which mode is selected, and the blue does not seem to suck at all.

At one stage after leaving it in 4WD on the muddy road, the 4WD light started to flicker and was mostly illuminated by the time we got back to the farm, but I'm still pretty sure it was not engaged.

I pulled the boot back from the actuator and it seems pretty good in there. Put in some grease for good measure. The shaft seems free enough, although I couldn't move it much with the car stationary, but I assume it would go in further with the wheels turning once the right spot was located.

I have a manual for it, but can't seem to find a good section on how the 4WD system works.

Anyone know how to troubleshoot these things?

Any help is appreciated.

Jeff

[bmurray2250]

Hi Jeff

When the engine is running the drive shaft to the front diff should turn easily. When the engine is stopped, turn the shaft again and see if it turns freely or locks. It should turn a bit and then lock.

[hybrid]

Thanks for the reply. I can turn the shaft freely with the engine off.
I assume this means that the actuator is stuck out?
Is it worth removing the two bolts from the actuator bracket to see if it will free up?


Edit: I just removed the yellow vacuum line and now the diff locks, so the actuator is working fine.
Obviously there was still some vacuum in the tank when I originally tried.

So I assume there is a switch connected to the 4WD lever that tells the ECU when I select 4WD, and it switches the vacuum solenoids to activate 4WD.
What's next? Remove/replace/check the switch on top of the tranny? Reaaaally don't want to take the tranny out.

[hybrid]

Ok, another update.
I got underneath it to feel around for the 4WD switches and found a wire that seemed to be disconnected. It was a single wire, yellow with red stripe and it had a white plug. I felt around above the transfer case and plugged it back in where it was meant to go.
This didn't fix my issue though.
I jacked the car up at the front and did some further testing. When I shift into 4WD, I can hear the solenoids, but there appears to be a bad connection because if I move the stick around, I can hear them clicking on and off. I originally thought the sound I could hear was a creaking sound because of the flickering they were doing.
If I'm lucky, I get the solenoids in the right place and when I spin one of the front wheels, it locks. Moving back to 2WD always unlocks. I very rarely see the 4WD light come on though, even if the diff locks. It flickers on and off now and then.
So does this seem like an issue with the switch that might resolve with some more use, or does it sound like a replacement will be required? I have been shifting in and out a lot, but does't seem any better.

[bmurray2250]

you may have an issue with the transfer case but the front drive shift not locking into place is another issue

[hybrid]

I don't think the transfer case has a mechanical issue because when I put it in 4WD, the front driveshaft engages. The issue seems to be whatever sends the signal to the solenoids to lock the hubs.
It does actually lock the hubs when the stick is in the right place for the solenoids to activate. That is until I wiggle the stick even slightly and it unlocks again.

[cookie]

this seems to be the most commonly refered to link regarding the dreaded vaccum system and flashing 4wd light, for an older pajero but principal is the same. I just installed manual front hubs so i never had to worry about it again.

http://4wd.blogeasy.com/

[Pauly Faulkner]

The 2wd detection switch closes the solenoid circuit and tells it to open or close(closed being open circuit as the solenoid in question is a normally closed one). 2wd switch is one of the two that are visible through a check plate under the console(on gen2 pajero it's there, not sure about challenger). it's one of the two closest to the levers anyways.

Yes the solenoids are meant to have power when ignition is on, the negative/earth wire goes to the 2wd detection switch and earths it out in 2wd and in any 4wd selection it leaves it open. The switch isn't on the lever though it's up further on a shift rail or somewhere there so it's odd that it flickers on and off with the shake of the lever, hope it's nothing to serious.

[hybrid]

Excellent info Pauly... what does the second switch do? Is that the High/Low detection switch?
Which one should cause the light to illuminate?

[hybrid]

I think I have had a bit of a win.
The "leaking" solenoid that I posted about in the other thread was bugging me.

Then it hit me - vacuum is supposed to leak from that "plug" on the yellow solenoid, but I had the lines on the wrong ports.
When the solenoid is activated, vacuum is sent to the actuator to hold it open. When you switch to 4WD, the yellow solenoid deactivates.

However, if you have the vacuum FEED attached to the upper port, manifold vacuum leaks from the "plug". What also happens is that the vacuum line to the actuator is blocked. Because the actuator is under vacuum when this happens, it remains under vacuum and does not allow the blue vacuum line to move the actuator.
So if you put the vacuum FEED to the bottom port of the solenoid, it gets blocked when the solenoid is switched off, and putting the actuator line to the centre port means that the vacuum that was in the actuator is then allowed to bleed out through the "plug".

I still have an issue with the 4WD light not always working, but it is now definitely engaging 4WD as I can feel it in the steering.

So the important part is done - I think I just need to play around with switches now to fix the light. Oh well... I have a spare set of solenoids now when they arrive

[hybrid]

Just an update on this one.
Having not used 4WD again for a while, this one has reared it's head again.
Switching into 4WD shows no lights on the dash. I can hear the solenoids switching on and off sometimes when I shift in and out of 4WD. Dash globe is tested OK.

Anyway, as we're about to head off to central NSW and have many KM of dirt to tackle along with the chance of rain, I didn't want to risk this not working.

I decided to make a more permanent fix. Seeing as power is provided to the solenoids in 2WD, I tested shifting in to 4WD and unplugging the solenoids. With them both unplugged, the hubs engage.

I found that it is pin 7 (third from bottom left when looking at the module and blue with white trace on my car) on the plug of the 4WD module behind the drivers kick panel that sends the 12V to the solenoids. It's labelled "Free wheel clutch changeover solenoid valve" in the manual.
I cut this wire, attached wires, and ran it through a switch that I installed in a spare spot beside the steering column. Now when I shift to 4WD, a flick of the switch disables the solenoids and engages the hubs.

Bear in mind that this will only work for you if you are in the same situation that I am.

1) Your 4WD shifter is working fine
2) Your vacuum compoments are all fine
3) Your actuator on the front diff is functional
4) You can remove the electrical plugs from the solenoids while the engine is running and the diff locks (check by jacking one side up and trying to turn the tyre)

It is also worth noting that you are provided no visual feedback that this has actually worked.
I'm actually hoping that with some use and lots of bumps and cattle grids that my 4WD detection switch will come good at some stage and I won't need this switch.
If left in the 2WD switch position, the original system will work as normal and this can just be used in emergencies.