I can feel and hear the transfer case engage...but the front wheels don't /won't pull also no 4x4 light on the dash....it was working a week or so ago..it kinda comes and goes...had the same problem for a while now but I need to fix it and not sure what to do..This is a 91 Runner with manual trans.
Any ideas...thanks guy's.

 

check the ADD system if your truck is equipped with it.

http://personal.utulsa.edu/~nathan-buchanan/93fsm/

 

Well, assuming no one has knocked the 2 vacuum hoses off, the culprit is usually the VSV's (vacuum switching valves) under the fuse block. One will be blue, itehr will be brown. I think the blue gets you 4WD, brown gets you back into 2WD. Made sure both are working and switching vacuum. If you get the green 4WD light momentariyl when shifting into 4WD, the vacuum hoses are backwards on the servo

 

wouldn't the engine run very roughly if it lost the hoses?

 

No, way too small of a leak, and the EFI unit would correct for the extra air, unless he has plugged injectors and it couldnt correct anymore as it was already correcting to the max (about 25%). The new OBDII cars can correct for a power brake vacuum hose off!!! Huge hole, runs like heck, whistles, and in about 10 seconds, runs as smooth as silk. Still whistling though.

 

replace all your ADD vacuum hoses. IF not I've heard that there is a switch on the side fo the transfer case which tends to go out. I think mine is going out as I tend to have an issue getting into 4wd every now and then.

 

No problem running the engin run perfect...just my 4x4 comes and goes...like i'll have it then I don't..the 4x4 light is on everytime the 4x4 is actualy working.

 

This my be the problem...any more info on this switch...the name for it ?

 

how to find it what it looks like.

 

here's two pics from the two different t-cases available....one chain driven, the other gear. the sensor is on the passenger side of both..

http://personal.utulsa.edu/~nathan-b...15componen.pdf
http://personal.utulsa.edu/~nathan-b.../6componen.pdf

 

same thing happen to me after replacing a upper intake gasket forgot to put the vacum hoses back! worked perfect ever since!

 

1991 4runner v6 5 speed: i have a problem when put my truck in 4x4 hi or low all my tires one at a time they stop moving for a sec and starts again then goes to another and does the same then hole truck jercks around its like when a person does not know how to drive stick

 

to see if that switch is the culprit, unplug it (there should be a disconnect right near tbe tcase) and test it with a multimeter. if you get a strong reading, then the switch is fine. odds are its the stupid vacuum hoses. i would try stuff like blowing out the solenoids or tapping on them when you are tying to engage 4wd, a combination of those things fixed mine when it happened to mine...

 

I second the vacuum hoses and voltmeter testing. Last night we had a snow storm and a bit after locking the warn heavy duty manuals and engaging 4wheel hi I drove maybe 5 miles when I started hearing a zipping sound coming from the front end and below me. At the time I felt the 4 wheel had come out of gear although still illuminated on the dash. I immediately down shifted which seemed to re-engage the drive however coasting a mile later the audible zipping whirring sounded again. I got out and unlocked the hubs and switched back to 2-wheel drive. Checking under the truck this morning I see some differential oil has leaked a small amount at the front end. The truck sat awhile and may have already been low on fluid or not stirred up enough. Anybody have any similar symptoms and if so, what was done to recover? I plan on taking it to my uncles transmission shop and have him inspect everything. I wont have time to do this as soon as I'd like, might I just be low on fluid and have a poor gasket? If not, can I expect to get away with a diff replacement and other?