I have a 1990 F150, 302, manual 4x4 with missing and disconnected vacuum and/or EGR hoses. The truck runs fine, but gets terrible gas mileage. I am in the process of doing a deep tuneup and would like to get the hoses and connections back where they belong which will hopefully improve the MPG. Is there a clear diagram/drawing/pictures somewhere that clearly shows the vacuum and EGR lines for the truck? My haynes manual and web searches haven't been much help. Thanks.

 

The smog systems have little effect on gas milage one way or the other but there are a couple common problems that do.

Does the truck have stock sized tires on it?
Have you pulled the codes?
Does it have dual tanks and if so do they both work?

Fuel crossflow between tanks was common, there was a TSB issued to add external check valves to supplement the internal valves that began to fail or get dirty with age. Check milage on both tanks, if one is a lot worse than the other you have this problem.
If there is a major sensor problem that will put the computer in open loop and fuel milage will take a big hit, so fixing the problems that set these codes can help a lot.
Oversized tires also impact milage in a couple ways, if they're just slighter bigger than stock(29") it's not gonna be much to worry about but if you got 36" mud boggers on it then that's a major issue.

 

Conanski,
Thanks for the response. The truck does have stock sized tires. I have not done the codes, I planned to run them AFTER I complete the tuneup which I thought might be more helpful. It does have dual tanks, but they both seem to function normally. However, I do appreciate the info on the check valves and I will fix that potential problem before it happens. Good to hear that the hose issues should not be a major issue, but it does bug me to see open connectors where there was obviously ment to be a hose. Thanks again for your response and input.

Loy