22re-efer

I have been messing about, trying to fix this problem for the past year, and also reading as much as I can on this forum and others, but I'm confused, and looking for some help guys. I have a '96 4Runner with the vacuum actuated add system. Over the past year, I have found that it will not always engage into 4wd. I have determined that the vsv under the hood is switching back and forth, and I have not found any apparent vacuum leaks in the hoses down to the actuator. Here is the scenario: Tonight I fired up my truck and pulled the lever into 4wd. No 4wd light. Popped the hood, and disconnected the vacuum hose from the 1-way valve which is inline, near the top of the motor, disconnecting from the diff side of the valve, not the motor side. I could hear air flow out of the hose for a few seconds and then stop. I plugged it back in to the valve, and checked inside the truck: 4wd light had come on. With everything that I understand about this system, I still can't figure out where the problem is. What is it that I am doing to 'fix' this problem by simply unplugging the vacuum line and plugging it back in? I'm hoping it might be just a matter of replacing the little plastic valve, but I don't know if I'm that lucky. After getting prices from Toyota for the vsv and actuator, I don't want to replace either, if I don't have to. Any insight would be appreciated. Thanks.

Duncan

justin_4runner

try removing the one way valve and see if it works fine. it sounds like u are getting vacuum on one side and causing it to not release when the vacuum is switched. if that makes sense.

22re-efer

Justin: Removing the valve causes the motor to idle high due to the vacuum leak that it creates. (I realize now, you mean to run the hose directly, without the valve.) I think I will replace the valve, and see if that fixes it. It almost seems as though the valve is sticking, and by pulling the hose off and putting it back on, it frees it up.

22re-efer

bripamy: Thanks for the info. I have tested and confirmed that I am getting 12v to each side when I switch in and out of 4wd. What I'm not sure of is whether I am getting vacuum every time. I talked to a Toyota mechanic today, and he suggested running vacuum directly to the engage side of the vsv, in essence bypassing it. If it switches in and out every time, it is the vsv that is the problem. If it doesn't, then it is the actuator. This makes sense to me, and I will try this.

On an a related note: Has anybody done the ADD bypass mod on their truck, and can you tell me if you noticed a dramatic increase in fuel consumption running the shafts full time? Thanks.

justin_4runner

if u do the bypass u will need a set of hubs to unlock them so it doesn't keep it all locked in, i wouldnt think that if u did the bypass it would change the mileage much.

22re-efer

So I bypassed the VSV by running the vacuum line straight to the engage side of the VSV, taking it out of the equation. So far, it seems as though it goes in and out of 4wd, without issue. I will monitor it for a while. This is a troubleshooting technique that was recommended to me by a local Toyota dealership mechanic. If you bypass the VSV and it fixes the problem, then the problem is with the VSV. If it does not fix the problem, then it is the actuator on the diff, or a problem with the lines running between. Toyota quoted me over $900.00 for a new VSV. That will never, ever happen, so I'm considering other options.

As it is right now, I'm running with the front diff 'locked'. Anybody have any direct experience with how this affects gas mileage? That's pretty much the only negative effect that I can foresee. I don't want to spend over a grand for manual hubs either, so I'm hoping that the mileage doesn't get significantly worse, and I'll leave it as is.