Intermittent 4wd (1 Viewer)

[Iceman25th]

I am trouble shooting my 1990 FJ62. 4wd is intermittent. Did a VSV replacement and that did not solve the issue. I’m not sure what to trouble shoot going forward. I have noted that the dash button does not light up but I still have 4wd but not reliable. I was under the impression that low was fully manual and did not involve electric or vacuum. The fact that at times it will work and other times will not is making this difficult to trouble shoot..
Any suggestions? Thanks

 

[RodrigzCrzr]

Check the vacuum actuator on the transfer case!

 

[RockDoc]

Weak vacuum from the engine, or tired diaphragm in the assembly at the transfer? After I cammed my engine (longer duration, lower vacuum) I noticed that front drive engagement wasn't as solid.

 

[Iceman25th]

Check the vacuum actuator on the transfer case!

Check the vacuum actuator on the transfer case!

Thanks for the idea.
Might try looking for part just in case.

 

[Iceman25th]

Weak vacuum from the engine, or tired diaphragm in the assembly at the transfer? After I cammed my engine (longer duration, lower vacuum) I noticed that front drive engagement wasn't as solid.

Thanks, Rock Doc.
Know anything about replacing that diaphragm?

 

[mwebfj60]

Does it hold vacuum and engage 4wd with a mighty vac? That diaghragm is stout. Check the vacuum lines from the VSV to the actuator. I’ve read the hard line portion corrodes and will leak.

Putting the shifter into low mechanically changes the hi/low gear and electrically triggers the 4wd...so similar to pushing the 4wd button, still ends up being controlled by the VSV and vacuum actuator.

 

[RockDoc]

Thanks, Rock Doc.
Know anything about replacing that diaphragm?

No personal experience. I think mwebFJ60's advice to check lines first is solid. Couldn't hurt to check vacuum reading at the source too if you have a gauge.

In my case with reduced vacuum, it would be fine once fully engaged, but I'd have to be careful to make sure it was fully engaged before getting on the throttle (hit 4wd button and coast with throttle closed for a second or two to get as much vacuum as I could).

 

[Iceman25th]

No personal experience. I think mwebFJ60's advice to check lines first is solid. Couldn't hurt to check vacuum reading at the source too if you have a gauge.

In my case with reduced vacuum, it would be fine once fully engaged, but I'd have to be careful to make sure it was fully engaged before getting on the throttle (hit 4wd button and coast with throttle closed for a second or two to get as much vacuum as I could).

I will try this to start. Will start tracking vacuum lines and see what I get. Is the actuator a part that can be obtained easily? Going to have to get under tomorrow and see what everything looks like for starters.
Thanks to everyone for the great input.

 

[Iceman25th]

OK, just spent the last hour looking for a vacuum actuator in the vendors section, no joy. Also looked for a set of vacuum lines, same result. I can probably make the vacuum lines but was hoping that would not be necessary. Anyone got those parts?

 

[mwebfj60]

Could be the VTV causing issues as well, I would think that would be a constant issue though. Worth checking out with the mighty vac though. There have been a few vacuum actuators in the classifieds fairly recently.

 

[89BIGBLUE]

My 89 was doing the same thing.
I found the hard vacuum line was rusted out at the near 90 degree bend on the frame, just below the firewall.
I was able to disconnect the larger diameter vaccum hoses just after the hard lines to the soft lines (stay with me here, sorry it’s wordy) and blow/suck the soft lines to verify the TC vacuum actuator was still working.
I trimmed out the rusted sections and have rubber vacuum hose in place now. It works great again.
I got some brake line to fabricate a new set of hard lines with, but haven’t gotten to it quite yet.

 

[Iceman25th]

This is very helpful. I can see from all that has been posted a path to take. Your post and the photos put the icing on the cake.

 

[mwebfj60]

Took me a bit to find these but might help

 

[Iceman25th]

Took me a bit to find these but might help

That is helpful. I can see my Sunday is full.