AsahiMan

ok i just kinda need to know where to start looking for common problems and fixes. i have a 91 4runner 4 wheel drive, 4wheel lever is on the floor type. anyway, the problem is when i switch the lever to 4wheel HIGH when i'm driving the 4x4 light turns on when the gas is being pressed. If i remove my foot from the gas pedal the light turns off. As i switch the lever the truck makes a small thud like its making a switch or something. I've been doing some searching and it seems that the 4x4 indicator is a TRUE way of telling if it is 4x4. but why does the light go out when i release the pedal. Does that mean its going in then coming out of 4wheel drive. Other scenario, got stuck in some pebble like rock ÅÅÅÅ the other day. only the passenger side rear tire was spinning. I put it in 4low and still nothing happened. rear tire was only one spinning. Do i need to reverse to get the truck into 4 wheel drive? should i have placed the truck in 4wheel low before getting stuck or will it not matter. just seemed that the 4wheel drive isnt working correctly at all. any comments or place to start..its early and i'm half asllep so sorry if these questions seem dumb. This is my first 4runner, and i usually dont deal with 4wheel drive vehicles. Just funny little japanese sport cars. thanks

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tc

Sounds like you have a vacuum leak. The ADD system that engages the front axle is vacuum actuated, so when you press the gas, you have enough vacuum to vercome the leak, but at idle you don't.

The "4WD" indicator is linked to the lever that engages the front axle, so it's a very good indicator of if you're actually in 4WD.

Search for ADD, vacuum, etc

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^VooDoo^

This is what your ADD vacuum controller looks like, Its on the passenger side fender.
The top hoses goe to a little tank under the passenger fender as a resurve,
the bottom hoses got to the diff.
Check all the hoses are connected right and have no cracks.
The little blue thing in the picture is a oneway valve, Make sure its working properly by blowing through it both ways and that it is connected right, This valve keeps the vacuum in the cannister while the engine is throttled.

Attached Thumbnails

 

4Mogger

You have no traction aid (limited slip or locker) installed in the rear axle so yes your 4WD is working properly--just not working to its potential.
Hi or low range dont matter much if your wheel speed though the pebble surface was where you wanted it and you had power that you liked.
One way to "cheat" the stock lack of traction is to actually apply the brake while staying on the gas when you get stuck. This serves to transfer power away from the wheel that is spinning and to the wheel that has traction. Sometimes a pulse method works best and sometimes steady pressure works best--just play with it. In the rocks if you have the manual transmission, I have had good success doing this with the engine off and using the clutch start cancel feature. The brakes prevent the engine from turning over fast enough in low range to start and it is a good way to effectively lock the axles in slow, creeping situation--say on roll over hill at poukeepsie gulch where one inch either way means complete and total destruction of the cherry 4Runner in an end over end rollover.

MMA_Alex

no, the 4wd is not working properly because there was no power to the front axle. The above advice in regards to the vacuum issues is a good thing to check out. We are assuming you have auto hubs correct?

trythis

It may not make any difference here, but auto or manual? Make a signature, it will help us diagnose your future problems.

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AsahiMan

yes the 4runner is the SR5 v6 with manual transmission. i assume they are ADD cause i dont need to unlock anything to 4wheel. Well the truck came with aftermarket wheels, which cover the hubs. but i assume manual locking hubs wouldnt have the floor shifter in the cabin correct? i will diagnose the vacuum line and see what i can see, hopefully something obvious....doubtful since there is vacuum when i'm on the gas, probably a small leak, we'll see.

MMA_Alex

I have a floor shifter, and manual hubs. It does sound as though you have auto hubs though, even if manual hubs arent locked in the 4wd light still stays on when the t-case shifter is in 4wd.

AsahiMan

Should there be vacuum coming from both hoses going to the differential?
Top hose has vacuum the bottom doesnt. other than that all hoses seem to be ok. anything else?

Thanks again guys

^VooDoo^

...... ok, Here goes.
In the picture there are 2 cellenoids.
THe Blue one is the ADD off, And has power when the transfercase is in 2H and cause a vacuum at one of the hoses at the diff.
The Blue one turns off when the put into 4H/L
The Red one is ADD on and has power when the T-case is in 4H/L and will cause a vacuum in teh other hose at the diff.
The red one is normaly off when in 2H.

BTW, I have ADD and My avatar is an example of what Manual hubs looks like, If you dont have the little twisty dials on your front wheels then yours is auto hubs, Has nothing to do with ADD ( Which you do have ) only the year of the vehical does.
Also in general all pre-electric 4x4 tranfercases have the shifter on the floor.

91 4Runner

Check the vaccum lines to the actuator. I had an issue like this a few months ago. I would have 4x4 sometime and sometimes no. It turned out there was a small leak in the lower hose (when it was covered with dry mud I had vaccum and when it wasn't I had no 4x4) easy fix. Just cut it at the leak and reattach (or if the line is now too short replace line... Hope this helps

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Corey

Guy's, auto hubs last year was '88.
Many confuse auto with ADD, and this is not correct.

ADD hubs you do not need to get out and turn the dial, those are manual hubs.
ADD hubs you simply move the 4WD lever to 4H and go, up to 50 miles per hour you can do this, hence the phrase "shift on the fly."
ADD hubs are the same as having manual hubs locked in all the time, hence parts are moving all the time.
That is why many do a manual hub conversion and take off the ADD plates.

Auto hubs are crap.
Auto hubs often will disengage when you back up on a trail, not good.

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AsahiMan

FIXED!! or so it seems. the vacuum lines leading to the diff were reveresed..weird. The 4x4 light now stays on and the truck feels like its is in 4wheel drive now.

maybe this should be stickied. anyway. thanks for the help.

i hope i'm not wrong and am in some way tricking the diff or light into thinking its in 4wheel drive.

response?

4Mogger

Drive it in a tight circle with the 4WD engaged on dry pavement-- you will know if the front end is engaged or not!