surferfrank

Could someone give me some advice on how to diagnose and fix a 4wd problem on a 1990 4 runner?

My 4wd light flickers and goes out on the dash. I thought I had 4wd, but I got stuck in Lake Tahoe this weekend. I had to put on chains!

I'm not sure how to fix a vacuum leak or the add system, but I'm willing to try. The friendly folks in Minden told me "the 4wd diaphram is leaking". Not sure what that means: Replace vacuum lines or the add system? How much are replacement parts?

I want to check in here before I drop more money into my truck.
thanks

mt_goat

This may help http://www.4x4wire.com/toyota/tech/add/ if you want to defeat the ADD system.

Memphis4X4

Actually, I used the outstanding search function that Yotatech has to find a post that I had made in an old thread which helps answer part of your question. Try this Thread

See if this helps. I fixed my 4wd using this method and all that was wrong was one of the vacuum hoses had a hole burned in it. If you light is flickering it might be engaging and then the vacuum is bleeding down and disengaging.

David

surferfrank

thanks...It looks like a vacuum leak from the thread you posted.

Where it's leaking is the big question.

I'm not sure about defeating the add system. It sounds kind of complicated.

Hopefully I'll be able to fix this problem before my next trip to the mountains, otherwise I may have to chain up again. :pat:

Memphis4X4

Defeating the ADD typically means that you convert to manual hubs. That requires money. Instead, I would troubleshoot the vacuum system just like I wrote in the other thread. The vacuum leak is not some major leak in your engine but will be somewhere at or after the vacuum solenoids that I refer to. Most likely it's at the vacuum canister in the passenger side wheel well. The leak will proably be due to a dry-rotted rubber vacuum hose or a hose that has been rubbed by brush while off-roading. That happens a lot to these hoses because they are in the wheel well and can be easily damaged. But......that's any easy fix.

David

surferfrank

I looked at the vacuum lines today following the last post. I found that the vacuum lines both draw air, yet the 4wd still doesn't engage. The light still flickers and goes out.

Any more suggestions before it goes to a repair shop?

I'm wondering if the ADD system has a leak inside. I want to be sure before I buy a replacement.

thanks for the help...

Memphis4X4

If you have vacuum at the diff then it most likely isn't your ADD. The problem is probably in your Transfer case. Click on the copy of the FSM section on the Transfer Case .

This is getting out of my area of knowledge. I let my transmission shop service my transfer case. If the FSM doesn't help, take it to a trusted tranny shop.

David

surferfrank

thanks for the advice. I'll try switching the lines just in case, but it looks like a transmission repair job($$$).

surferfrank

Just an update...
The vacuum problem ended up being a switched vacuum line at the transfer case. They are color coded and the engine rebuilder switched the lines.
Thanks for the info. It helped me figure out this problem.

Memphis4X4

Great Job!!!!

Isn't it a good feeling when Yotatech helps you fix something and you don't have to take it to the dealer and spend $$$$.

I'm glad you got it fixed!

David