I recently purchased a 1998 F250 4.6L. I found the previous owner had rerouted the vacuum lines to try to get around emissions. I have corrected everything in the engine bay area I believe. My question is regarding the vacuum line connection under the dash just to the upper right of the accelerator pedal. The previous owner had rerouted the black vacuum line from the connection through the firewall. What should the black line have been connected to before they changed it?

 

The small vacuum line would run to the control **** on the heater / air cond to control defrost / dash / floor vent....... the vacuum runs INTO the control ****, the OUT to 3-4 different small cylinders to stroke the duct doors open and closed.


There may be other line, but these are the ones that come to mind first.

 

I may have a more complicated issue. When I bought the truck, a black piece of tubing (referred to as the black line because I can see the other colors exiting the junction, this line was run underneath the steering column through the firewall and tee connected to the piece (sorry I can't recall the name) to the upper left of the brake booster and the other side was connected to the vacuum line entering the EGR valve top. My guess is the idiots were trying to trick emissions. I corrected everything in the engine bay but my concern now is the order or arrangement of the of the lines exiting the connection.

 

Maybe a picture would help?

 

I know it sounds crazy but I hadn't really paid attention to the air flow in the truck. I had heat so that worked for me. After your reply, I tested the vent doors. No matter what setting I selected, air blew out the defrost vents. I'm actually relieved as I feared the modification would have impacted emissions. I'll get back there and reconnect things. Thanks a million.

 

if you disconnect the vacuum line to the heater controls/ ducts... the DEFAULT is to stick on the defrost selection.