Located under the driver side mid cabin before the tank and after the tranny is this 3 hose plug. I took some pics in hopes someone can identify it and tell me if it is seated properly, and if this would contribute to poor fuel mileage. Went from 21mpg to 12mpg seeming over night - realistically a couple of fill ups. I can smell fuel near the middle to rear driver side. No smell from the engine compartment. Cappy, if you're out there; hook a brother up?

 

Tcase vaccum switch

 

It looks like the transfer case vacuum switch.

 

That's what it is,I'd check the fuel system,lines and other connections..

 

+1 yes

 

Possible that the transfer case vacuum switch has failed and the vehicle is in 4wd all the time which would decrease fuel mileage.
And / or there is a vacuum leak which would also decrease fuel mileage.

I believe the switch can just be removed/replaced. However if it has failed there is a good chance there is fluid in the vacuum lines which is not a good thing. Is there fluid dripping from the HVAC controls? Remove one vacuum line at a time, label its position and check for fluid inside.

Suggest searching the forum on this topic for details.

Good luck.

 

Looks to me like the 3-way rubber junction thing is not pushed far enough down on the prongs of the switch, for it to be properly sealing vacuum. Also looks like the rubber thing and lines are quite damp; not sure what that is. If you pull the lines from the switch and fluid drips out, you'll need to replace the switch and clean out your whole vacuum system if you ever want HVAC controls and 4WD to work properly again.

But this won't cause such a large drop in fuel mileage. Keep looking.

 

Thanks guys, I feel a little better. It didn't look like it was seated properly. The 4x seem to work fine, engaging/disengaging. Double AA21830; you are right, it is damp/wet. I'm not sure from what exactly. The vacuum system clean out sound like a real ... The saga continues...

 

Ok, quick update. The reason I was under my truck and discovered, and with your help identified the poorly seated t-case vacuum switch; was because I was checking for some form of leak/damage in the fuel system, as I had a drastic drop in mileage and the smell of fuel near the middle to rear driver side. No smell from the engine compartment.

Well as it turns out, the switch lines were not seated properly and needed to be turned 2/3rds for the one way pin to go in. Here's the interesting thing, as per the above advice i removed lines, check'd for leaks; there was none and then re-seated it properly. Now the 4lo does not work. Prior to this change, even with the poor seating all 3 opts. worked 2hi, 4hi & 4lo? Any ideas???

I changed the fuel filter, as it seemed like it has never been done before or God knows when. As I did that, the smell from the driver side mid went away and has now shifted to the drivers side rear. I now think it's the canister. The old filter was full of deposits and particles. I've noticed an all over drive-able difference instantly. ie. increased throttle sensitivity, lower rpm idle, lower rpm 1st, 2nd, & 3rd gear change. Am I making this up or is this to be expected? This may be part of the problem. No fuel line leaks found.

 

Further Update. There is a fuel line leak as it turns out, it's just before the rear wheel well, leaking bad. Anyone change one of these out? Any tricks, tips and advice appreciated.