cwarren38

I just bought a 1990 f150 custom. Its a 302 efi 5 speed 4 wheel drive. After filling the tank 3 times, I am getting 6.6 mpg. I know it should get way more than that. Also the guy that had it before me, apparently did a number to the vacuum lines. There are 2 vacuum lines blocked off, one on the throttle body between the 2 black rubber hoses from the air filter, and one on top of the plenum. there's another line coming off the black box on the frame rail beside the radiator (assuming something for emission) that is also not connected to anything. Also there is a small vacuum line by the coffee can that is not connected to anything. The two red lines are on the can, but the one that is not connected looks to be off white, or possibly a faded pink. What do these lines go to? Can anyone provide a pic or schematic of the vacuum lines. I know this probably has something to do with the gas mileage. Also, the check engine light is not on. Should I still check to see if there is any codes?

Marc D

Broken or disconnected vacuum lines almost always relate to poor fuel economy. Most of what you are describing as "plugged, disconnected or missing are fuel emission systems. The can is a vapor recovery tank from the gas tank. The hoses from the air cleaner are engine emissions gases being returned from the motor to the air intake. The black box may be the ABS controller.
Yes, I would check for codes but it may require taking it to a shop since OBD2 testors don't always read stored codes. Make sure the check engine light is operational as well. Look in the owners manual at which fuse is for the cig. lighter. It is the same one as the CEL is connected to.
Vacuum line diagrams can be found in most shop manuals or as a Google image specific to your year and motor. Good luck