Still working on the 1990 F-150, but I am almost done. I am in the process of getting all of the hoses and wiring hooked back up. The only thing I am having an issue with are the two vacuum hoses that come off of the throttle body and "Y" into one. When I took every thing apart I am pretty certain that it was not hooked to anything, and I can't see anything that it goes to. In the meantime I'll try hitting some manuals to see if they have anything, but I could use some help. I'd like to get this thing wrapped up today.

 

I believe the Y-connection led back through the single line to the vapor canister. Someone with an early 90s should be able to confirm. My 95 has a single line to the TB and canister. But I do have a TB from a 93 that has the connection you describe. The 93 engine is no longer in a truck for me to view complete system.

 

Yep, those lines connect between little nipples on the drivers side of the TB assembly and the charcoal canister on the very front of the passenger side frame rail.

 

Thanks guys! Now I know for sure it wasn't hooked to anything. There surely isn't enough hose to make it to the canister. I'm pretty sure it was just tucked under the upper intake when I took it all apart. Looks like I am maybe an hour or so from hearing this beast run again.

 

Ok, I just checked on this. There is no fitting left for the line to hook to on the vapor canister. The lines from that lead back around the rear of the intake and hook up to some relays or something mounted on the same bracket as the coil. There is a lonely yellow tube not connected to anything that runs to that relay as well. Perhaps it is supposed to hook to that? I haven't found anything yet that the yellow emissions tube runs to. It isn't very long, so it can't go far.

 

Here is how all of those vacuum lines should be run.

The dash lines are the ones with the "Y" you asked about.



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Maybe this would be a little clearer:


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I think you are confusing the vacuum resovoir(VRESER) which is on the passenger inner fender and should be connected to the solenoids via small plastic black and red lines, with the vapor canister(carbon can) on the passenger frame rail in front of the motor that should be connected to the throttlebody via larger black ruber lines.