I have two questions. First, i got a 1985 F150 XLT Lariat Gold with 302 (5.0) EFI. My first question is, when i crank up my truck when its warm, it wants to stall out, and if it don`t die (which it does several times), it runs REALLY rough. it has had 1000 dollar worth of tune up not even a year/20,xxx miles ago. it runs rough till i start driving down the road. once i drive it and hit around 20 MPH it smooths out. reving it up dont help. Its ruining my battery and i wiil not go buy one till i fix it!!!!

Next question, The vent selector that changer heat to the vents, floor, and defrost. Mine will cut on and off but it always blows out the vent. Whats wrong with it?

Thanks in advance!!!!

 

A very common malady with our trucks as they age. In the ductwork there's a flap that diverts the air to the floor. Either that is screwed up or the vacuum "motor" that controls it is screwed up, probably the former.

 

Have you asked the computer what is wrong? It knows what it things the problem is and until you fix that the truck is probably going to run poorly. Go to the stickies and look up the procedure for pulling codes.

 

i Thought these trucks didn't have the ability to pull codes?

 

This is a sign of having a vacuum leak in the system. On the passenger side of the engine compartment, there is a black round plastic reservoir [sometimes is a metal can]. Check for cracks and follow all the vacuum hoses and look for vacuum leaks.

The HVAC system defaults to defrost when there is a loss of vacuum. This normally happens when you are accelerating or climbing a hill.

Listen for a hissing sound.

 

All the trucks with EFI have computers. Go find the procedure to pull codes and find out what the computer is mad about.

 

i know this post is old but if someone has a snapshot of this i would like to see how tis is connected cause my 84 is have the same issue with the vent not deflecting throughout the truck. how is the black ball to be hooked up!!

 

I've answered this question in the OP's own thread.