4wd issues…..

[rolling7high]

Hello,

Long time reader, first time participant.

I have a 1997 4Runner, V6, manual transmission, 4wd, no rear e-locker.

I currently have no 4wd. I have no actuator engagement on the front differential and no light on in the dash. The transfer case does shift into 4hi, 4lo, and turns the front drive shaft.

Troubleshooting I have done:

-I have inspected all vacuum houses. –No cracks

-I have inspected and tested all electrical connects on the transmission, transfer case, front differential actuator, and vacuum switching valves. I discovered a broken front differential indicator switch, which I replaced. (the new front differential indicator switch provides a leak of fluid, exciting new development) All the other connects are in good condition.

Next, I put the 4Runner on blocks.

-I switched the vacuum hoses from the bluish/green vacuum switching valve with the vacuum hoses on the reddish/brown vacuum switching valve. This activated the front differential actuator and engaged the differential. I turn a front tire by hand to simulant movement and both tires tired.

-I placed all the vacuum hoses to the original positions. I shifted the transfer case into 4wd, removed the lower vacuum hose on the reddish/brown vacuum switching valve (this vacuum hose is outgoing to the front differential actuator), and turn a front tire to simulant movement. The front differential actuator engaged the front differential and 4wd light came on in dash. I return the vacuum hose on reddish/brown vacuum switching valve. I had 4wd, everything is normal, everything is great! Next, I shift from 4wd to 2wd and back to 4wd and I have nothing, again.

The reddish/brown vacuum switching valve is providing consent outgoing vacuum in both 2wd and 4wd. The bluish/green vacuum switching valve only provides outgoing vacuum in 4wd. I have unplugged the electrical connect to the reddish/brown vacuum switching valve and it still provides outgoing vacuum in 2wd and 4wd.

My question: is the reddish/brown vacuum switching valve supposed to provide constant outgoing vacuum? (I have scoured the Internet for this information and could not find it. Please provide link) Any suggestions of where to troubleshoot next. Could someone proved FSM information on the vacuum switching valve, so I can look at the information?

Thank you for your help

 

[Grenvilleter]

Probably the switch on the transfer case. Almost exact same symptoms as mine was, I cannot tell you which one it is however. Sorry !

These switches are prone to failure when not used for a while.
with that said, they may also respond to a good cleaning once removed.

I have not tried cleaning yet but they are a simple ball contact switch. I suspect a slight oxidization from lack of use as they do not seem to be problematic for those who use the 4x4 option regularly.

 

[TheDurk]

No, vacuum should occur at one VSV or the other. Your problem is likely NOT the contact switches, (apologies to Grenvilleter) as the one-side always on, one side switches is not a fail scenario that a bad switch could produce, IMHO. A bad switch could make the VSV go to the incorrect state (2wd vs. 4wd--vacuum to brown or green), but not a state that should never exist (vacuum to both sides.)

You need to determine if you have one of two causes:

1. The brown side VSV is bad.
2. An electrical problem further up the chain.

To do this, you need to take a 12V test light or DMM and see if the 12V+ signal switches from side to side as you go from 2wd to 4wd. If it does, and I suspect it does, this confirms that the VSV is bad. If it remains always on to the brown side, then the problem is up the electrical chain. The vacuum should cease to pass when the 12V+ signal is removed.

Or, if you don't have a DMM, just unplug the brown side in both 2wd and 4wd. If vacuum continues to pass in both cases, or even just one, VSV is certainly bad.

My money is on a bad brown-side VSV.

 

[rolling7high]

Thanks Grenvilleter and TheDurk,

I have tested the 12v electrical current on the VSV. The brown side of the VSV has 12v current in 2wd and the green side of the VSV has 12v current in 4wd. However, the brown side is giving outgoing vacuum to the actuator when it has 12v current or not.

It is also my estimation that the VSV is bad, but I wanted to throw out the question to get input. I have not been able to find any specs on the VSV and I don't know anyone with a 4Runner to compare information.

I will work on tracking down a VSV.

Thanks, again.

 

[Grenvilleter]

No apologies necessary TheDurk. It was a couple years ago now and as I recall back, I had a bad VSV as well.

I swapped out the VSV's from a donor truck an, I could engage after the swap but could not dis-engage without removing pwr from the cct via key off.

The dealership wanted $700.00 for a VSV module (both sold on the mount plate).

Unfortunately, this was only one of my problems but at least I could have functional 4wd and left it at that until a time comes when I had to check out the xfer case switches.

Opportunity came this fall when I swapped transmissions and found with the new xfer case, unit goes in and out of 4wd as designed but, due to another faulty switch on the replacement xfer case, my dash light now fails to tell me when the t-case is in neutral.

Oh well... I can live with that but I really should try to identify which switch does what on the t-case and try to remove and clean them up to see if they can be made operational again.

It could help someone else out but it's been darn cold and or snowing and I don't have a heated garage so I'm not inclined to "putter" to see if I can repair the switches.

I hope this thread can at least help you or point you in the right direection.

As an afterthought, as I recall, I tested VSV's resistance and they both had continuity and the same resistance values but I swapped them in spite of not seeing anything blatantly wrong with the originals. I should recheck them to see if I made a mistake in reading the resistance values.

 

[rolling7high]

On Sunday, I went to the local "Pick'n Pull" and found two complete VSVs (brown and green valves) from two Gen2 4Runners. I bought two so I could compare the parts and so I would not have to go back for another.

I replaced the brown VSV on my '97 and everything is working, again. I also have spares for whatever reason.

Thanks for everyone's help.