cackalak han

I'm a noobie when it comes to car mechanics. My 4WD system worked fine a couple of months ago, but then yesterday, I tried to click it on (I have the push-button 4WD) but the indicator light wouldn't come on. I tried it from driving, parked, reverse, 4HI to 4LO...and didn't work. This morning, I put it in 4LO, and for some reason, it worked. Then, I put it in 4HI and drove around for a while, turned it off, and now it won't turn back on.

Anyway, I know there are a bunch of threads on this, but I didn't see one with any pictures. I just wanted to know if I'm checking the right things. First, I checked the vacuum lines in the engine bay. From the pic below, I'm guessing it's the lines going into the green valves? I couldn't get those off easily, and I didn't want to break those plastic valves, so I tested the line the I outlined in a red dotted line. The suction was there.



Then, I looked under the car, and looked at the place where the front and rear driveshafts met, and I'm guessing that this is the actuator? If so, the line that I dotted in red is the vacuum line that I checked. There was no suction when 4WD button was pushed.



Does that mean that there is a leak somewhere between the vacuum hose under the hood and the actuator?

I just wanted to make sure I was checking the right things, before I started tearing things apart.

Thanks for any input.

And just in case I'm not checking where I should, can someone point out the correct parts from this pic? Thanks.

midiwall

Yeup, you're in the right spot, well done!

I have a thread from a year ago that may help (https://www.yotatech.com/forums/f16/diagnosing-no-4wd-lock-up-58634/) but my guess is that you've seen it.

The first line you found was the vacuum feed from the manifold, so there'd best better be acuum there lest I doubt your engine would even run. The blue thing is a check valve so that vacuum doesn't leake back into the manifold.

Past that, there's a double T in the line that feeds two solenoids and a vacuum reserve tank that's mounted up under the driver's side fender, at the very front.

The acuator on the front diff works on vacuum for both engage and disengage. The vacuum is directed by the two solenoids on the driver's fender well (where your red line is headed). With the button out, one solenoid is enegized and vacuum is routed to one side of the acuator. Hit the button, and the other solenloid pops on (the first one turns off) and the vacuum is now applied to the other side of the acuator. A nice side point here is that the light on the dash is "real". It only lights when the locking collar actually slides over and locks up the diff.

For troubleshooting, take a long screwdriver and place the tip on each solenoid, put the handle to your ear while having someone hit the button. You should be able to clearly hear the solenoids click when the button is pressed. If not, then the solenoid that you can'y hear could be bad - or there's an electrical problem at that point.

If you can hear the solenoids click, then there's VERY little between them and the acuator on the diff. If there's no vacuum on the alternate tubes down there (that tracks with which solenoid is engaged) then there's a plug in the line.

If you find that you are getting vacuum on both tubes, then you should be able to hear the mechanism slide in the diff. Do this with the engine off, there's enough reserve in the vacuum tank to flip it in/out a couple of times. If you can't hear the sliding, then the acuator may be bad.

Good Luck!

callmej75

Ok up in the bay next to the fender where your vacuum line comes out of the VSV (the valve with the vacuum lines for 4wd) and goes to the intake...notice there is a check valve in the line then it connects to the intake? Start your engine and pull that check valve out and if you have suction coming from the intake...and not when the valve is on...then what I did was spit in it and suck it back out. Best fix I ever did for a nasty cause!

Potomacduck

I had a similar problem. The 4WD would turn "on" but it would not turn "off."

If it is the actuator, is there are tech link for replacing the acutator? What is the proper name for this part and how much does it cost?

cackalak han

Thanks, Midiwall and callmej. I have not gone in to diagnose the problem further, but yesterday, the 4WD system worked with no problems. I'm hoping that it was just due to the lack of use of the system, but this weekend, I will investigate this further.

callmej75

Sounds like lack of enough vacuum sometimes...would definately check that check valve if it does it again and if not that....go through Midiwall's procedure.

cackalak han

Ok, I will. Just to make sure we're talking about the same valve--in the first pic, it's the blue check valve right above the dotted red line, right?

callmej75

Yeh...doublecheck and make sure that vacuum line from the valve plugs into the side of the intake plenum into a 3 way filter that screws in the side of the plenum. Hope this is not confusing...

midiwall

Also, if you pull it off to check it, make sure you put it back the right way. It's a one-way valve, so if you put it in backwards, you won't have ANY vacuum at all.

cackalak han

^^ Oh, good point. I'm glad you mentioned this beforehand.

thelasteaglescout

I happened to reverse the check valve on my 4runner and my 4wd started working? Previously I wasn't getting any engagement. And yes, it would engage and disengage with the check valve reversed (theoretically getting no suction). Is there a chance when previous work was done on my 4Runner that they incorrectly reinstalled my vacuum lines? Or is my reservoir just charged and by taking the "live" vacuum out of the line the system is some how working as it should?