I drive a 3rd gen but my buddy has a 2nd gen that he found out doesn't go into 4wd in the middle of a blizzard. I could use some help trying to help him sense i am not very familiar with the 2nd gen 4wd system.

What ive found so far. Transfer case goes in H4, L4 H2 no problem but the front does not engage. There is no vacuum going to either hose at the add solenoid on the diff. there is no vacuum going to the vacuum tank. the 4wd valves has the correct resistances. i checked to see if the valves had any voltage change at the plug and it did not change, stayed at 0volts. that was all i had time to check.

Couple of questions. Where is the vacuum sourced from? I pulled the vacuum hoses of both ends of the filter and didn't get any vacuum on either side. Followed it to the engine where there was no vacuum either. It seems like it went under the intake manifold but i couldn't tell. Ive looked at the pdf of the FSM but its hard to tell where i should even start. Any advice would be great. I don't have the truck with me so i cant just go run out and check something but anything would help.

edit:forgot to mention 3.0 5spd.
Thanks

 

For future reference, you can suck on the vacuum hoses to manually cycle the actuator and engage/disengage the ADD differentials.

Anyway...start troubleshooting:

http://personal.utulsa.edu/~nathan-b...26addcontr.pdf

 

That was the PDF i found and was looking at. where do you suggest i start? whats the most likely problem area?

 

Usually a disconnected vacuum line or someone accidentally swapped the two lines:
- http://www.off-road.com/trucks-4x4/t...tem-19259.html

 

Well you're not getting vacuum at the tank and the system is vacuum operated. Common sense tells me that's a good place to start.

The source of the vacuum is the intake plenum...there will be a bunch of vacuum hoses connected to the passenger side. If you're not getting vacuum at the plenum, either the engine isn't running or the port you're using is clogged.

 

That was my thinking!!! There were 3 plugs coming out, the one going to the valves had nothing on it. i pulled one fight next to it and there was vacuum coming from the hose not the intake (odd to me). that was as far as i got, i had to go to class. My buddy is gonna drop the truck off tomorrow night so ill play with it this weekend. just trying to get some prelim info for now.

 

I just fixed my 92 4runner. My 4WD light was not turning on. I replaced the two hoses that go to the diff. I bypassed the vacuum valves and ran the diff straight to the intake, but still no 4WD light. I don't need 4WD often so I put it off for a while. I'm going 4 wheelin' this weekend so I started diagnosing it again. It ended up being the wiring harness connector going to the switch on the transfer case. Make sure the wiring harness is OK if the vacuum hose checks don't fix it. My hoses looked ok, but I replaced them anyways. There is a series of events that needs to happen before the light goes on. The first in line is the transfer case switch. The transfer casae switch signals the vacuum solenoids to apply vacuumm to the diff. When the accuator locks the axle to the diff the light 4WD will turn on, but only if the transfer case switch is working. After fixing my electrical problem, I could hear the vacuum solenoids clicking as I shifted in and out of 4H. I then had to reverse my vacuum hose changes so the diff would disengage. I have manual hubs on my car, so don't bypass the vacuum valves if you still have ADD hubs. Good luck...

 

Having this problem on my 01 occasionally but I believe mine is electronically actuated.

 

Just take off that whole stupid add set up. Take the actuater out, jam hose clamp around it, so it stays engaged full time and put some manual hubs.
You can still switch from 2 to 4.
Did it on my 4runner and love it !!!

 

thanks for the heads up on the electrical, after studying the diagrams for a little bit(mechatronic engineering student) thats what it was looking like it was going to be. as for the manual hubs, thats in the future for him i think, it most definitely is on my 02, but in the time being he needs it to just work. He working up in Tahoe for the winter.

 

With your buddy's car being a 5-speed like mine, it's very likely that the harness was damaged when the clutch was replaced. I'm pretty sure that's how I damaged mine since I changed my clutch in the driveway. With the transmission and transfer case being so heavy it had no problem ripping the two pins out of the plastic connector.
It's hard to see as well since the switch is on the top of the transfer case.

BTW the harness is on the passenger side. It is the second to last connection on going towards the rear of the car. It is only two wires.

 

I second that! i did it on my 1990 'runner and it is SO much better!! Picked up some hubs off a '86 in a junk yard for $40 bucks, repacked them, slapped them on, then got a hose clamp and you have to open up the front drive line and slide the piece over so it covers the gears and the teeth line up, then put a hose clamp on the shaft to keep it from sliding out of place. You know have a solid front drive shaft and you can lock your hubs just like everyone else in the wheeling community lol without the heavy heart, hoping your ADD will work when you need it.

Here is the write up i followed and it isnt a difficult process but this write up illustrates everything.

http://www.4x4wire.com/toyota/tech/add/

 

I'm not sure what you mean by the filter but I'm guessing you mean the actuator on the diff. Follow the vacuum lines up to the engine bay. They should end up at a valve bank on the passenger inner fender by the fuse box. Check there first.
If your in a blizzard with 2wd, just go SLOW, you lose if you die and someone else will get your Toyota or worse, they'll crush it!

 

you should try to manually apple vac and see if u can get it to engage i had some problems but i just switched the vac lines around and it was fix have not touched it since

 

What's an apple vac?

 

one thing i notice when i put mine in 4wd is a click from under the dash area, there is a relay under there that if the sensor in the transfer case is working should be clicking over, and that is what gives the power to the vacuum solenoid to give the vacuum to the actuator. one common mistake when people pull the actuator off the diff and put it back on they dont always get the fork in the right location when reinstalling it, so it wont slide the sleeve over the shafts and 4wd wont work too.

 

In certain high-desert apple farms, the apples are collected in 4wd trucks, which use an "apple vac" to gently remove the apples from the trees.

If the 4wd fails to engage, you can sometimes use the apple vac to apply vacuum to the actuator.

I think that's what he meant.

 

yes apple vac got it right on the head! dam computer and its auto correct!! but what i meant to say is "apply vacuum"

 

im working on the truck right now. where is the fuse box in the cab?? thats the first thing i want to check. its not in the drive kick panel like my 02

nvm, where is the add relay? as in where under the dash?

 

so xfer case switch works. i have vacuum going to the storage tank. still no electrical signal at the air valves on the pass wheel well. i think the last thing to check on the electrical side is the relay. havent checked the vacuum manually cuz i cant find hoe im willing to suck air through that doesnt taste like gas or oil.

ive been poking my head around under the dash found fuel pressure relay, flasher relay couple small one that i dont kno what they are. the fuse is good.

whats next?