Mileage

[1994xlt]

Find out what code it's throwing. In my experience the check engine light going on and off usually indicates a misfire. That could be a bad plug/wire/coil pack, cracked head leaking a little coolant in and fouling the plug, carbon fouling on the piston, insufficient/too much fuel pressure, other things probably.

Coolant temp sensors going bad used to be a problem, it would tell the computer a wildly inaccurate temperature and they would run really rich or really lean

Back in the day fuel pressure regulator failures were really common too and that would cause noticeable changes in fuel mileage

Not telling you to replace any parts, just do some testing.

Okay well got my truck plugged in today and it doesent have a memory so it showed no codes there gonna do a key on engine running test at work tomarrow to see if this code pops up, hopefully it does, my dad and me tried to fix this vacuum leak again because it broke off again but I’m going to get some hose at work tomarrow, I turned the truck on and this hose does nothing at all so im not sure if it’s really creating a vaccume or not or if it only does it at certain times. Anyways we pulled the plugs and noticed there old so I’m gonna get new plugs and throw them in just for peace of mind since I’m here what plugs do yall run in these older 4.0 engines? From what I’ve found there’s a few different kinds of plugs from motorcraft for them