ragz

1991 4Runner, a/t, 3.0L V6 (pretty much stock other than the 31" tires it was bought with).

As the title says the 4wd simply doesn't engage (no light in dash and no engagement of the front wheels). Now there were two significant events that occured since the last time I had the vehicle in 4wd. First off the short block was replaced (due to the infamous head gasket issue and subsequent loss of oil 6 months after the vehicle was bought) and secondly an incident when the wife was driving it 2 weeks after the short block work was done.

She was driving along some back country muddy road and says she was in 4wd (but can't remember if the light in the dash was on or if the front wheels were truely engaged) and as she approached pavement she reached down to push it from 4H to 2H but grabbed the wrong lever and instead proceeded to shift from Drive to Reverse while still rolling forward (are you cringing like I was when I first heard this yet??). She's quite convinced that she was under 10km/h (6mph) when this happened but there was a sufficiently loud clunk and the final result was that the engine itself stalled out. She started it just fine and continued on her way home with no further problems. I didn't find this out til months later when I needed 4wd to get thru a snow bank and lo and behold I didn't have it. So everything appeared normal and I had no clue of anything for a couple months of regular 2wd use.

Basically my question is this, am I wasting my time following vacuum and electrical lines for the ADD (as searching revealed as a common failure point) to determine the reason for the failure? Is it a fairly safe assumption that the situation described to me by wife pretty much implies that some damage has been done to the transfer case and/or related mechanical components of the system? I have no idea if shifting from Drive to Reverse in 2wd would result in the same noise described to me or the engine stall (nor am I about to test this to find out).

This is the 1st vehicle I have ever had with 4wd (and actually this is the wife's, not mine), all my vehicles have been fwd cars so the 4wd system is pretty much unknown to me. Just a warning that when it comes to these systems I'm definitely a newbie. Thanks in advance for any comments.

NorCalVP

When the engine was replaced, the vacuum lines for the ADD were probably bypassed durring the hookup, I had a similar problem on my Tacoma, but it turned out the the ADD solenoids were blown. Check for the red(kinda brown) and blue solenoids that have vacuum lines attached to them that go down to the Front diff. Probably disconnected somewhere...

Memphis4X4

The D to R shift that your wife did shouldn't have messed up 4WD if the truck ran fine afterwards.....it would have blown out the transmission and not necessarily the transfer case of the 4WD. I definitely would start troubleshootoing. I had to do this on mine and found the problem and was able to fix my 4WD system pretty easily.

The 4WD system is pretty straight foward. When you shift from 2Hi to 4Hi, the 2 vacuum solenoids that NorCalVP mentioned switch and allow vacuum to pull on the front diffenential. This then activates the ADD and engages the front hubs with differential and at the same time causes the transfer case to engage the front drive shaft so that it will turn the front diff gear/front half shafts/hubs/wheels.

So, if I were you.....Here's what I would do:

1) With truck running, transmission in Park and parking brake engaged, I would move the selector from 2Hi to 4Hi.

2) Raise the hood and on the passenger side of the engine compartment, right next to the fender there are a bundle of vacuum lines that hook into the solenoids that NorCal mentioned....they are colored blue/green and red/brown. Disconnect the vacuum lines into them and see if they pull on your finger when you seal the end up with your finger tip. That means you have vacuum into the solenoids. If not, look inside the front pass wheel well and find the vacuum canister just inside the front bumper. Check the vacuum lines going in for breaks/cuts/splits....these can get damaged by trail debris. This canister acts as a reservoir to store/boost the vacuum to provide enough to operate the front diff when needed. Once there is vacuum at the canister, go back to the solenoids and make sure that they suck coming out of each of the solenoids. If all of this works then the problem will most likely be in the 2 vacuum lines going down to the front diff.

3) Drop the front skid plate and look at the top of the diff and find the 2 vacuum lines going to it. Pop off the line and make sure they suck. If not, trace the lines up through the left side of the engine compartment. Be careful to avoid any of the moving engine parts, i.e., fan and belts, because remember that the engine will be running while you are doing this. I found that one of these 2 vacuum lines and touched the exhaust header and burned through. I spliced the two ends together using a vacuum coupling fron AutoZone and fixed my 4WD.

4) If every vacuum line is sucking......and it still isn't shifting into 4WD, then the problem is in the transfer case. An Auto Transmission shop will have to look at it then.

Hope this helps,

David

Flygtenstein

I have bumped reverse when going forward in drive and all the truck did was stop. I put it in park, restarted, changed my drawers and all was fine. Probably traveling around 10 mph in 4wd at this point, it was between trails.

Trace the vaccuum lines and make sure they look like the pictures on assorted sites. The fact that the dash light is not illuminating means that something else is amiss as well. That is a seperate connection.

ragz

Ok I cheated a little here. I applied vacuum directly and what do you know the 4wd appeared to engage. So given the temperature outside (fighting sub zero temps here right now) and with my lack of a garage I simply packed everything up and dropped it off at the shop that did the short block work for me. Ok ok, so I'm cheating a lot but given that it appears to be a vacuum line problem I figure the shop that screwed it up in the first place can deal with it at their cost. Thanks so much for your help guys, I'll keep you posted as to what comes of this.

Cmar

Hope you dont mind me jumping in here, but it's a similar prob..


My friend has a similar problem with his 2nd gen, But when he clicks the 4wd button on the transfer lever, the light on the dash comes on for a second and then goes out. There is also clicking from the solenoids. We jacked up the front wheels and they spin freely with the button out, but when the 4wd button is pressed, they lock for a second and then spin freely again....

Any suggestions



Cheers Guys

ragz

Sure enough, when the new short block went in the vacuum lines running down were routed too close to the exhuast manifold and well it's pretty obvious what happened there. The lines were replaced (an rerouted) and voila, 4wd exists once again!

No worries Cmar, jump on in. Although I can't offer any suggestions as to why the the system would engage like that momentarily and then kick out again. Hopefully somebody else has a suggestion for you.

gavkenn

Hi, I have a 4wd problem with my 97 4runner ltd.. it won't engage. I checked the vacuum lines to the solenoids and both line have vacuum. But when I check the vacuum into the solenoids after attaching the pipes, there is vacuum into the brown solenoid, but none into the blue solenoid. Does this mean that the blue solenoid is bad or is it something else? Please advise ASAP as I can't get out of my garage!!

Thanks in advance.
Gav

Hollywood

Y'know, I've been seeing a lot of 4WD not engaging, and not much beyond it not being the solenoids. I wrote a similiar thread recently in which my wifes '97 limited w/ 3.4 does the same thing as gavkenn's. When the button on the xfer lever is pushed, nothing. I have vaccum going into the solenoids, but they don't switch when the button is pushed. I swapped the output lines and the front diff/driveshaft engages, but not at the xfer case. That tells me that whatever the problem is, it is failing to engage the front drive solenoids AND the xfer case (as well as the light). I replaced the 4wd computer in the drivers kick panel as a longshot, and nothing. SOmeone mentioned a relay on the passenger side, but nobody can tell me the location of it. I even read out the 4wd switch itself, and it wirks fine. Somebody please help us before summer gets here and I am stranded from getting up the beach!!!