Ok everyone! 4wd issues on 94 runner

I’m hitting up all the forums. Down here in Az for the winter and left my new 17’ Tacoma in Ak. Love yotas so I bought a 95 4runner 3.0. Done a bit of work to it and of course after I bought it the 4wd started being funky. Know one seems to know what’s up. It has ADD.

The issue: 4wd engages fine. As soon as I start accelerating the throttle starts cutting in and out like I am mashing the gas pedal over and over. I try to break through it into higher rpms and it keeps doing it up to 30+ mph all rpm ranges are affected. As the throttle cuts out the rpm drops. After at speed and let off throttle she coasts just fine. Today I replaced egr modulator and every vacuum hose in the truck. 2wd is flawless with no problems at all in the throttle. Runs great otherwise. I am seriously stumped and trying to tap into as many resources as possible. Any help or ideas would be appreciated. I head back to AK in mid feb and would like to get this fixed. I’m either going to sell it or keep it for next winters AZ trip. I need a lower 48 Riv and I love the vehicle minus this mystery.

 

If it only happens in 4wd then it is the ADD vaccum lines. They usually dry out and split. This will cause your motor to have a major vaccum leak and lean out.

You have 3 options:
1. Best. Buy ifs locking hubs, slide ADD arm in axle housing to lock and hose clamp in place, and gut all the ADD vaccum lines and vacuum switches.

2. Cheapest. Leave ADD hubs, lock ADD arm, only shift tcase to 4wd when offroad/snowy roads.

3. Most frustrating. Start checking all the vaccum lines and vaccum switches. They are mostly located on drivers side up by radiator. Check yotatech for fsm pics of locations.

 

Thanks for the feedback! I replaced every vacuum hose in the truck today including all ADD lines in the correct locations. I guess it could be the switches but since 4wd is engaging wouldn’t that mean the switches work?? I have def thought about doing the add delete. Will probably go the cheap route and leave the hubs until next year I would get locking hubs. With the add hubs on and the axles locked how much strain would that put on the front?anything I need to know? my family and I are driving this vehicle quit a bit and will continue hopefully for a few future winters.

 

You are sure that the ADD axle is locked when you throw the lever into 4wd? I would have someone shift back and forth and listen for a hissing noise while the ADD actuator is locking/unlocking.

When manually locking the ADD arm, you may get some extra vibes from the second axle now spinning. It will feel just like when a non ADD truck is driving around with its hubs locked in, which many of us do all winter long in snow country.

 

You might want to inspect the vaccum cannister in the wheel well. I have seen them rust out or crack.

Post 3 in this thread has some good descriptions of most ADD locations. I know it dosent directly deal with your issue, but it may help.
https://www.yotatech.com/forums/f116/4wd-failing-engage-20461/

 

Thanks for the link. I’m pretty sure the sleeve is over when tcase is engaged. I had to put in 4hi to get up a dirt road the other day and I can crawl out but it’s just lurching the hole time. I agree with the vacuum since 2wd is totally fine. I will check that canister for sure. I realized the only line I didn’t replace was the one going to the canister through the fender... shit I guess I’ll do that tomorrow and keep my fingers crossed. Thanks again.

 

On the 3rd gen T4R I had, the ADD solenoids were on the driver fenderwell. Each had a hose going in and out. The out lines went down to a hardline near the steering system. This hardline ended and had short Hoses to connect to the ADD Actuator.

Just making sure all the Hoses are identified.

 

Yep. Pretty much the same on the 95 except on the passenger side. I changed out all the hoses and are all in the right places. 4wd engages fine but the engine runs like a three legged dog when the throttle is pushed down. I will investigate the canister today.

Interesting though when I pull the vacuum lines to the ADD after running in 4wd the lines his and release vacuum which would make me think that the canister is good otherwise it wouldn’t hold vacuum.

 

Do you think a tps sensor or loose throttle cable even though there are no issues in 2wd?

 

Ok. Have still been trying to figure this out. I decided that I would just do the add delete but before continuing on I went ahead and capped all the vacuum ports related to the ADD. decided to see if the prob persist just from engaging the transfer case. Well it happened. The ADD was cut out of the equation and as soon as I shift to four hi my rpms drop and any throttle caused a stutter. So I decided to make sure it was electrical and disconnected the switch at the transfer case and all is well when shifting to 4hi. Obviously though I’m not really engaging 4wd due to the lack of vacuum. Could the relay under the dash be causing an issue?? If I do the ADD delete and keep transfer case disconnected i could still have dependable 4wd without the indicator light correct? Just curiose what the transfer case is telling the ecu that would make the throttle cut in and out during acceleration. Again all vacuum ports are capped to ADD and under 2wd conditions all operations are perfect. Good power, even idle, no signs of vacuum leak in 2wd?? So stumped.

 

The switch on the tcase can be cut and one wire ran to the back of the gauge cluster and then ground the other wire off the switch, this will give you the 4x4 light. The switch just grounds out when the tcase is shifted into 4wd. I dont have access to my notes or my EWD to tell you which wire at cluster connector and which wire on switch to ground/run, but I may make it over to the shop tonorrow and take a look.

I had to do this on my current truck but not for same reason, I did a 3.4 swap into a early truck and it was easier to run it outside the ecu harness.

 

Thanks for the input. I always like to diagnose before going the other route but I’m tired of coming up short. Just want to throw the lever and have 4wd. Will be back in AZ next winter and will prob go for the locking hubs. All else runs really well and only has 200k think I’m going keep it as my lower 48 rig. This is the same model I learned how to drive on so I’m a little emotionally attached.

 

Actually I realized I have a FSM from a 93 4rnr here. This is the ED of the 4x4 light and ADD. Ground the white/black wire from switch to body and run the green/yellow to green red at c12 at the cluster.

 

The indicator lamps are always hot, the switches just switch the ground.

 

Perfect! Thanks for digging that up. Will get to work soon. Appreciated!!

 

Also try unplugging the tps and then shifting into 4wd. If the idl setting isnt correct the ecu can sometimes act weird. Unplugging it will pop a code, but it also makes the ecu run in a default mode.

 

Will try this as well. Will hook up tomorrow and try rulling out tps.

 

Here is a better pic of that page

 

I have to admit I am a total novice with electrical. I was hoping it would be a straight forward issue. I ordered a new/ used ADD relay hoping that this would be the issue someone told me that even if I heard it clicking it could still be bad messing with the voltage. I can return it if it doesn’t change anything. I don’t have a volt meter with me as I am in AZ for the winter and don’t feel like purchasing one for down here. Strange thing though after I unplugged the relay to test the transfer case the rpms went up a little?? Drove around with transfer case engaged and no surging. Once again all is well with transfer case switch disengaged. Interesting with switch in place and relay disconnected and transfer case in 4hi I get a small increase in rpm. I guess I am just chasing my tail at this point. Maybe I will try going back to ground zero and disconnect the diff switch next but all that does is control the 4wd light correct? Sorry for the ramble and thanks for all your previous feed back.

 

Ok. New development. I unplugged the tps. Had higher idle but when switching to 4wd everything worked as it should. I found a straight away and floored it throut 1,2,3rd without any hesitation in throttle. I’m guessing now that either my tps is bad or the setting is off?