There is alot of info on this forum about putting a 20 gallon tank into an older yj but I was unable to find a good write up on it so I figured I would take a stab at a write up. I am no expert so if any info needs to be corrected, please feel free to do so!
Finally got some good weather yesterday to get some work done. I picked up a 20 gallon poly tank to replace my steel 15 gallon tank. The fuel pump in my 15 gallon tank was shot and the poly tank had the fuel pump, sending unit, skid plate and filler hoses included. Plus I wanted the extra 5 gallons.
Started pulling out the old tank:
Steel tank is out:
Side by side comparison:
The sending unit on the poly tank is rectangular while the sending unit on the steel tank is round:
The connectors on the two sending units are different. Here is the connector on the steel tank sending unit:
And here is the connector on the poly tank sending unit:
The way to fix this is issue is to cut the connector off both sending units and solder the old connector to the new sending unit:
Old connector on new poly 20 gallon sending unit:
Now while i have no tank underneath the jeep, I want to cut an access plate in the tub. The reason for doing this is to make the sending unit accessible from the top so that I don't have to drop the tank ever again for repairs such as fuel pump, sending unit, gauge readings etc.
Access plate with new 20 poly tank installed. I was off on the cut by about half an inch but no biggie, I can still pull the sending unit out easily:
Put some foam weatherstripping around the cutout to keep exhaust fumes from entering the cabin area:
Cut a piece of steel with the angle grinder to cover the cutout. Used 4 self tappers to secure it to the tub. It was cold when I was finishing up so I didn't paint the plate but I will shoot it with some spray on bedliner to match and prevent any rust issues:
Now after getting everything hooked up and ready, I tried starting the jeep but it wouldn't fire and the gauge was reading 3/4 of a tank with no gas in the tank. I had a bad ground. After talking with Que, I learned that the ground for the gauge and the sending unit are the same and that I can relocate it to the frame chassis. I cut the ground at the connector and ground it to the chassis by the back drivers side body mount. The gas gauge now read empty, put a gallon in it, started the jeep and it fired right up! Thanks Que!
New 20 gallon poly tank and skid installed:
Driver's side shackle clearance:
Passenger side exhaust clearance:
There is one thing I would do differently if I were to do it again:
I would have cut the old connector off the frame harness and used the new connector instead of cutting the new connector off the sending unit and using the old connector. the reason for this is the newer connector is smaller and easier to fish through the access plate.
Some good info:
The sending unit and fuel pump of a 91-95 2.5 will fit the older yj's. No need to swap the sending units. There is a different pressure rating on the fuel pump, but the regulator will ensure the right amount of pressure is sent through the throttle body.
There is a white baffle in the bottom of the tank that will become warped and cause the float arm to read inaccurate. Just pull it out.
I wanted true empty so I used an ohm meter to test the sending unit. The ohms on the gauge are 0-90 with 0 being empty and 90 being full. I bent the float arm to sit in the bottom of the tank reading 0 ohms. This gives me a true empty. Full will be off by about 5 gallons but that's no big deal!