Earlier this week we got a significant snowfall, so I went out and planned to run my errands with no trouble - running in 4WD. But to my dismay, the truck would not go into 4WD.

I did a little reading and I suspect that my problem is vacuum related - at the VSV. I'm 99% certain that the front drive shaft is turning. I have no dash light tho and the truck definitely stays in 2WD.

I haven't had a chance yet to take a serious look at it. But I did eyeball under the hood to try and locate the 4WD VSV. Do any of you guys know where it is?

I found one on the passenger fender well but I think that one is for ABS. And another on the drivers side firewall - but I'm not sure that is the right one. I haven't been able as yet to crawl under and trace the wiring from the transfer case.

This is what my truck looks like:

 

Don't sweat the wiring, just look for a tube from each VSV (there are two, one brown and one blue) going into a single large tube heading down to the front diff. If '95 is like later years, the twin ADD VSV's sit on the drivers fenderwall.

 

Yup I found them on the left fenderwell. I have vacuum at the input to both, but no vacuum at the output of either.

Is the switch on top of the transfer case?

 

Today I bypassed the VSV's. I connected direct vacuum to the tubing normally connected to the VSV that has the orange electrical connector. I then pulled the transfer case lever into 4WD, heard the familiar click of the relay behind the dash - and the 4WD lite came on as well.

I drove it around, and it was fine!



What surprised me tho is that I was able to take it in and out of 4WD. I would have expected the front diff to remain locked and the dash lite and everything else to remain active. But nope. The way I have things connected in the above photo, all is working 100% normally.

I want to do a proper repair of course, but I did not expect this. It's a relief however to have 4WD available as I continue to troubleshoot.

 

So now that the weather has warmed up, I did some maintenance etc. and decided to troubleshoot the 4WD issue.

With the truck in 2WD I turned the key to ON, unplugged the connector to the 2WD VSV and measured 12v. Also measured 0v at the 4WD VSV. Then I pulled the transfer case lever into 4WD. I then had 0v at the 2WD VSV and 12v at the 4WD VSV. So I started thinking that 4WD VSV must be faulty because this winter I bypassed it to get into 4WD.

Then I looked at the dash panel and saw the 4WD indicator ON. It went on and off as I moved the lever back and forth. So I started the truck and moved it and verified that indeed it was going into and out of 4WD as normal.

So it's working. And I did nothing,,,,,

 

Things get stuck from not being used .How often do you shift into 4wd

Then there might have been moisture that was frozen now with the warm weather it was all thawed out

 

Hey wyoming9,

That's just what I was thinking.

I'll put it into 4WD more often as a preventative measure going forward. At least for now I can cross this task off my list.