Valvoman

My 1993 4x4 system does not engage. The PO most likely never exercised the system and I think that the actuator assembly on the front diff is stuck.

There is vacuum all the way down to the actuator assembly and pick up has never been hacked or modded.

When I throw it in 4H, the front drive shaft locks, so it's not the transfer case.

Without a vac gauge, does this board have any suggestions to get that assembly unstuck---any ideas if it can be torn down or do I need to replace it?

Much obliged.

RJR

Are you sure the vacuum is hooked to the right port on the actuator. You might try swapping the hoses and see what happens.

You can remove the actuator mechanism from the diff on the driver's side pretty easily. That will allow you to inspect the sliding collar and the actuator fork. You'll need to drain some fluid first so it doesn't spill out when you open it up. It's a simple mechanism - just a sliding collar moved by a fork which is in turn moved by a vacuum actuator.

Here's the pertinent manual page http://personal.utulsa.edu/~nathan-b...le/24disas.pdf

RJR

Here's another URL that may be of some use as to how to get into the actuator.
http://www.4x4wire.com/toyota/tech/add/

AKHeathen

possibly the tcase actualtor switch or wires, but you say it gets vaccume to the actuator when you put it in 4, right?

Valvoman

Thanks everyone...

I really messed this post up....

When I put it in 4H (or 4L) it does not engage. I checked the VSV blue connector with a multimeter and it does not get a reading when switched to 4H....and the brown connector always has current.

So, two questions....
1] could I move the brown connector over to the blue and see if it works without issue just to see? and
2] is the t-case switch that critical for overall operation and can I get an accurate ohm reading on it if removed?

Also, the front drive shaft locks in to place when I put it in 4H...so it works properly.

RJR

You can swap the electrical connectors, or swap the vacuum lines to the actuator (or at the VSV's) to see if the mechanical parts are working correctly. If you switch the vacuum lines and then put the xfer case into 4wd, you should get actual 4wd operation if the actuator and mechanics are OK.

The transfer case switch and the ADD relay (under the dash above the steering column, possibly labeled "horn relay") are important for disconnecting the front differential when in 2wd and connecting it when in 4wd. You'll want to get the root cause figured out in order for everything to work as it's supposed to.

This should help you with your troubleshooting. http://personal.utulsa.edu/~nathan-b...26addcontr.pdf

AKHeathen

i don't have the schematic, but i belive it powers the vsv when you put it in 4wd, and grounds it when it engauges at the t-case, then there is an indipendant switch in the front diff is totally independant and comes on when the front diff is actually locked in (i know that last part as a fact) so if you get power toit he vsv, then ground the other terminal, it should lock the front diff in, ruling out the diff as the problem. you may have to spin the front tires to get it to show 4wd once vaccume engauged.

RJR

Pretty much correct. The ADD relay is a single pole double throw switch that either applies power to the "unlock" VSV when in 2wd, or the "lock" VSV when in 4wd. The ADD relay coil always has power, and the other side of the coil is either open when in 2wd, or is grounded when the xfer case switch detects 4wd.

Since only the unlock VSV is getting power for the OP, it would appear that the ADD relay is not switching, either because it's defective, or because the switch in the xfer case isn't properly grounding the ADD relay coil when in 4wd.

Valvoman

I've read other folks saying that their ADD relay provides an audible click. This true? Mine does not...and is it hard to replace?

My truck is a manual gearbox BTW.

RJR

Mine makes an audible click, but just because yours doesn't doesn't mean it's bad. I'd do some troubleshooting with a multimeter before I replaced the relay. It's more likely you have a bad connection between the xfer case switch and the relay.

The relay should have the following wires going to it:
- 2 brown wires. Both should show a steady 12V with the key on.
- Green/white wire should be 12V in 2wd, and 0V in 4wd. This wire comes from the xfer case switch and is grounded when in 4wd. If the relay isn't clicking this is most likely your problem
- Solid green should be 12V in 2wd, 0v in 4wd. This is the control wire to the 2wd VSV.
- Pink/Grey should be 0V in 2wd, 12V in 4wd. This is the control wire to the 4wd VSV.

Let us know what you find when checking these wires.

AKHeathen

you pul the vsv and test it by blowing in it energized. a lack of click could simply be a little trace oil or something, not necissarily meaning bad, but it switching flow correctly is key.

Valvoman

Looks like there is a fail safe notch on the blue and brown connectors, meaning they cannot be swapped.

With engine running, the brown connector always has 12v, even when I shift in to 4wd (and drive the truck forward a bit).

When I swap the vacuum lines, nothing happens BTW.

The trans switch is easy enough to get to. I'll pull it and see if it is operating. Could it be as simple as that $30 part?

AKHeathen

if you can bypass the vsv with a barb and manually actualte it that way it will let you know. btw, it needs vaccume to do so, so has to be running. when the engine is off mine always pops out. it will indicate 4wd mechanically when it enguages. it will help you rule out it being mechanical in the front end.

RJR

When you say "nothing happens", do you know for sure that the differential is not engaged, or are you just relying on the lack of a green 4wd light on the dash. If the xfer case switch, or the wiring to it, is bad, the green light will not light even if the differential is engaged. The only way to tell for sure is to jack up one front wheel and see if it will turn or not with the xfer case in 4wd. If you swap the vacuum lines it should shift into engagement and you should not be able to turn the front wheel while in 4wd. And, as AK says, none of this works unless the engine is running. Also, as AK noted, you might have to rotate the front wheel an 1/8th of a turn or so for the ADD collar to be able to slide into engagement.

AKHeathen

lol reminds me when i went 4xing years back. a guy asked me where to get the 4wd indicator, etc.... i thought nothing of it. we drank around the fire and i went home the next day. like 45 miles later i got home and noticed a little oil when i went to take off. the bastard stole my 4wd indicator switch and pigtail while i was sleeping....... i was pretty floored, not because it was stolen (iirc like 40 bucks or so for both) but because he didn't plug the damn hole and let me drive off, potentially tasting my front diff..... some people's kids..../rant.

Valvoman

I pulled the relay from under the dash, it reads Fuel Pump Relay...I assume that's it?

I tested for continuity as per this site: http://www.off-road.com/trucks-4x4/t...tem-19259.html

It passed only one of the continuity tests (terminals 1 & 4). So, am I on the right track?

If anybody has skills with electrical, please post up and check me.

RJR

1-2 are the coil, so should show continuity of a few hundred ohms. 6-3 should be connected in the idle state, and 6-4 should be connected when the relay is energized.

Make sure you pulled out the right relay. Compare the wire colors to the colors I listed in my previous post.

Also check the wiring and operation of the transfer case switch before you go any further. The wiring is the most likely cause of your problem.

AKHeathen

6 and 3 should also read, though probably not the same. 2-4 is from the vafm and 3-6 is from the ignition switch during start. both turn the fuel pump on. 1-2 should be off (open) normally. if 3-6 reads nothing, the relay is bad, and it will not pump fuel during cranking...... but it does not sound like you had a problem with the c.o. relay before.......?

RJR

This thread is focused on the ADD system, not the fuel system. Thus pinouts of the c.o. relay aren't relevant here. Toyota uses the same relays in various locations and vehicle models, so the label on the relay shouldn't be given too much importance. I think my ADD relay is labeled "horn relay". The important thing is the wiring harness and the pinouts, which I posted above, taken directly from the official Toyota wiring diagram. If the relay doesn't match those descriptions, chances are you're looking at the wrong relay.