Help With Diagnosis - 4wd Not Working

Hello all. I've been trying to get my 4wd working on my '98 4runner Limited (apologies for posting in the first gen section, but I believe the ADD system is the same as 1st Gen Tacos. Also the smartest folks on TW have first gens ).

I have confirmed that my transfer case engages and the front drive shaft spins in 4wd, but the 4wd dash indicator light never comes on and the front diff actuator doesn't engage. So I pulled the 4wd actuator off of the back of the front diff. I'm thinking I shouldn't have done that, and should've ruled out the ADD vacuum solenoids first. The actuator appears to be totally fine (fork moves freely, and nothing appears damaged).




If someone has the FSM pages for how to test the Transfer Position Indicator Switch on the actuator with a multimeter, and could share, that'd be great.

My next question is how should I orient the actuator upon reinstallation? The fork pivots up and down and slides left and right. Because of the struggle to remove it and jocky it out of the vehicle I have no clue how it was oriented when I pulled it out.

Lastly, should I hear a noise from the 4wd vacuum solenoids in the engine bay when I push the 4wd selector button? I hear the transfer case actuator engage when I press the button, but nothing from the engine bay or front diff area at all. Thanks for any assistance in advance.

 

IIRC, you can hook up a handheld vacuum pump to the clamshell actuator and see if the fork engage/disengage.

You might want to take a look at the vacuum switch that the vacuum line is coming from as well.

 

Okay cool I'll have to try that. I'm leaning towards it being that vacuum switch because I would think it would make noise when I press the 4wd selector.

 

Thank you for this sir.

 

Let me know if there's anything else you need and I can try and dig it up for ya

 

So my Transfer Position Switch tested fine for continuity (thanks again @Strictlytoyz for that test info).

So my replacement 4wd vacuum solenoids showed up today. So I resealed the actuator into the back of the front diff and replaced the solenoids. I can hear the solenoids clicking when I push the 4wd button (I didn't hear that before), so I think 4wd is fixed. Won't know for sure until I can fill the diff back up (waiting for the Permatex to cure first). Will update this tomorrow after I test that.

 

So update and hoping for some further diagnostic help from those smarter than I:

4wd is still not working (at least the light isn't illuminated on the dash after 4wd button is pushed -doesn't even flash).

Considering putting the truck on 4 jack stands tomorrow to confirm 4wd isn't engaging.

Does anyone know how to test the 4wd vacuum solenoids functionality? I put in new-to-me (but still used) ones from eBay and had a friend confirm he heard them click when I engage/disengage the 4wd selector button.

I probably should've used a hand vacuum pump on the actuator while it was out of the truck, but I could move the selector fork by hand, so I assumed all was well.

Is there anything I'm missing?

 

FWIW when we got our 96 4Runner Limited, our 4wd didnt work either, I think the previous owners pretty much never tried using it. I googled it a bit and found a suggestion that was something like to swap the vacuum lines to the VSV (I think) then to try actuate the 4wd a few times and then put the hoses back to their proper spots. Surprisingly enough it worked and now I just pop it into 4wd every so often to keep things lubed and moving.

Here is a post with suggestions:

 

One more question:

Can a vacuum leak elsewhere in the engine bay prevent the 4wd solenoids from having adequate vacuum pressure to engage the front diff actuator?

There's some suspect-looking vacuum lines (specifically the one crossing the plenum and going into the back of the throttle body), and I wonder if that's my problem.

 

That's interesting. I will have to try that. If it's not that I'm wondering if it's not more of an electrical issue. Perhaps a bad transfer indicator switch (sensor) on the Tcase causing no voltage to get to the front diff vacuum solenoids.

 

If jacking up the truck gets you nowhere here's more troubleshooting for ya



Assuming you have no vacuum leaks, if swapping your vacuum lines engages 4wd it's gonna be an electrical gremlin. I'll do more digging on testing the 4wd vacuum system

 

Thank you for this @Strictlytoyz.

I'm really hoping for a vacuum leak, and hoping to not have to go digging down the electrical gremlin rabbit hole. I'll start on these first thing tomorrow and report back.

 

There should be two vsv's located on the inner driver fender area. A blue one and an orange one (VSV2/VSV4). Can't remember which one is 2wd and which one is 4wd. What you can do is pull one of the hoses off from either of those vsv's that goes down to the ADD actuator and start the truck. Place finger over nipple on vsv. If there is vacuum that is your 2wd vsv. If there is no vacuum, try placing truck into 4wd...could be your 4wd vsv. If you find it is your 2wd VSV, put that hose back, and pull the other. Shift into 4wd, put your finger over the nipple, and see if you have vacuum. If you get vacuum the vsv's are not your issue. If still no vacuum, and both the ADD switch and 4wd selector switches are working properly you have a bad vsv. Lastly, ensure the hose coming off the vacuum tank didn't get disconnected somehow. Here's a diagram of the vsv system.

 

Excellent. That graphic really helps simplify the troubleshooting.

 

So update:

I got the 4wd working. Ultimately using a hand vacuum pump connected directly to the 4wd actuator on the back of the front diff was able to engage 4wd. From there, the vehicle's vacuum ADD solenoids seemed to be able to engage and disengage the 4wd on their own. I then cycled the 4wd on and off (in both 4H and 4L) multiple times, to ensure everything was working smoothly. Thank you all for your advice and pointers I'm this diagnosis

 

Awesome, glad you got it sorted!

 

I was under the impression that swapping the VSV lines does pretty much the same thing here by using the engine vacuum to pull and move the actuators to loosen them up. Glad to hear things work now!

 

I read that too, and tried it (didn't work). Perhaps my actuator was just a little hung up in there, beyond what the VSVs could move.

Honestly hooking up the vacuum pump directly to the actuator idea was a total crapshoot, and I just got lucky.

 

Essentially yes, either way it's working now