I think I read some where that you cant do the 15-20 gal tank conversion on a TJ?
I did, took me longer than 20 minutes though
Drop the tank, pull the sending unit and cut the small tube.
Don't know how accurate this info is but could be nice if its true?
Here's how to "enlarge" your TJ gas tank, written by an anonymous contributor:
Take down the tank and gain access to the top. Unscrew the sending unit/pump/filter and pull it out. It holds about a litter of fuel inside to keep the pump cool, so lift it straight out and tilt it back into the tank.
The column is more like a telescoping unit. It can slide up or down. Tabs on the side allow it to click in two positions. 15g and 20g. Sliding it down lowers the intake of the whole assembly, where before it sat about 4.5 inches above the tank bottom. The float acutally drops because of this making the whole system fairly accurate now.
I don't know about yours, but my fuel gauge lied all the time. Empty ment I had 4 gallons left and it would always drop hard on the last quarter. Now it's consistant all the way through.