Why is the gasoline gage moving up and down

Greetings Jorge,

This typically happens when there is a loose float unit, bad connections, or faulty sending unit on the fuel system. This is also a symptom in these years of a gauge cluster going bad. When you say moving up and down do you mean with motion or it is at a standstill just randomly changing the amount of gas that it registers?

There are a number of parts that can create this effect They are listed here as well as a link to a forum with a wealth of knowledge on these issues from ford.

Ford Forum of Fuel pump issues

I would start with checking connections and then moving through the rest of the parts.

Answer excerpt from ford forum " This issue has been known by Ford for at least 6 years. The purge valve gets stuck open. The resultant vacuum pulls in hard enough to buckle and collapse the plastic fuel tank, which also causes damage to the fuel pump (which is inside the tank, under the bed.). This condition can also result in fuel being drawn into the canister and soaking it in fuel. All of this can result in wacky fuel gauge readings, rich/lean O2 sensor codes (P2196-P2198) P017x and P045x codes, vacuum leak codes, etc. If the evap canister incidentally ends up getting soaked with fuel, one can also have hard starts (dieseling/run-on starts) or cut-outs after refilling. (on a side note, it's the same thing that happens to the evap canister if one regularly over-fills their gas tank) "

I hope this helps you out!!

Cheers!

Monte