15 to 19 Gallon Gas Tank Conversion for the TJ

Congratulations! You have bought a 97-99 Wrangler SE, complete with a 15-gallon gas tank... Capacity like that is nothing to write home about when you have a vehicle that only gets 19mpg tops stock, going downhill with a tailwind. I was lucky to squeeze 220 miles out of one tank. After the conversion that number jumped to about 280. The pre-91 YJ's had two separate 15 & 19-gallon tanks for the different models produced. After 91 Chrysler cut costs by just producing the 19-gallon tank, but installed longer fill tubes in some so they would only fill to 15 gallons. It has been debated if they carried this trick over to the TJ's. There are some that believe the fuel gauge or sending unit is calibrated so the 15-gallon tank will show empty when you have 4 gallons left. Do not believe this unless you have some comfortable walking shoes and a gas can! I have found that Chrysler indeed carried over the same cost cutting trick on the TJ with the longer filler tube, and when the gauge says you're empty, you better believe it. I'm going to guide you through the steps needed to convert that 15-gallon tank to the elusive 19-gallon tank. If you were planning to install an aftermarket gas tank skid (which you really should), this would be a great time to do it also, as you will only need to drop the tank once. I performed this conversion on my TJ at the same time I installed a Kilby gas tank skid. I have a detailed write-up of that also in the Tech stuff section.

Installation Instructions

First things first. Make sure you can get the tank empty as possible as you will be literally armpit deep into the tank, not to mention make removing and re-installing the tank a bit easier. You should also install a new fuel pump seal when putting things back together. They're only ten bucks at the dealer. Okay, now it's time for me to nag. Please use common sense when performing this conversion. No smoking or open flames in the area. Try to perform work in a well-ventilated area. Use jackstands to support the vehicle (not just jacks!) Keep all small children and pets away from the supported vehicle and work area. Use safety glasses, and I also recommend nitrile gloves if your skin is sensitive to gasoline or solvents. Now let's get to work!

First things first, make sure you have a level solid surface to work on. Disconnect the negative battery cable for safety, and chok the front tires. I found it makes the job much easier if you jack up the rear end, place jackstands under the axle and remove both rear tires first, otherwise they'll just get in the way.

Next step is to remove the eight screws holding the filler ring, cut the zip-tie holding the axle breather tube, and disconnect the ground strap.

Now it's time to disconnect the electrical connections, fuel and vent lines. There will be a small red plastic piece (pictured below) that holds to connectors together. The tab will have to be pushed to the left with a small screwdriver as the whole piece is pulled down. Remove the EVAP hose (the smaller one) by pulling and twisting (be careful not to bend the metal tube). Disconnect the fuel line by pinching the gray tabs together with your fingers and pulling the hose from the metal line. Watch for dripping fuel!

Next place a jack under the gas tank and remove the 7 nuts holding the tank on the frame. Slowly lower it down while guiding the filler tubes around the frame.

You're going to need a wide flat-tipped screwdriver and a hammer to remove the large ring holding the pump in place. Place the screwdriver against one of the tabs & use the hammer to tap the ring loose COUNTER clockwise (opposite the direction the picture shows).

Once the ring is out of the way, carefully pull the pump upward from the tank. Make a mental note of the orientation of the seal, this will make installing the new one a little easier.
Now for the fun part. If you reach inside the tank you will feel two filler tubes, one will be larger than the other. Take a razor blade on a scraper handle (pictured right), and rock it back and forth with firm pressure against each tube about one inch from the top of the tank. This will allow you to cut the filler tubes without having to worry about plastic pieces in the bottom of the tank. Take your time, as reaching into the tank may be awkward.
Let's get that thing back together! Once the tubes are removed, install a new seal on the fuel pump (you did remember to get one before you started, right?) and carefully place the pump back into the tank. As you compress the pump assembly, make sure the seal is seating properly and not binding. Once in place, re-tighten the large ring by turning clockwise by hand. You should be able to tighten the ring without it wanting to "pop" off. If not, check the pump. It may not be seated properly, OR if you had installed an aftermarket tank skid, the straps may be too tight. Once the ring is on as tight as you can get by hand, use a same flat tipped screwdriver and hammer to turn it one quarter more turn.

Time to re-install the tank. At this point I recommend using at least two jacks (I used 3!) to raise the skid & tank back onto the Jeep. The reasoning behind this is that I've found the front bracket tends to hang up on the trackbar unless the skid is brought up at an angle. Before raising back up make sure all your hoses and electrical connector are where they need to be when it's time to connect them back up.

Guide the filler tubes back through the frame as you raise the skid/tank back into place, raising the front of the skid up first to clear the track bar. Once the lip of the skid has cleared, raise the rear. Frequently check that none of the hoses or wires are catching on the frame. Once the skid is in place, re-install the 7 mounting nuts. Reconnect all fittings and re-install the filler ring.

Re-install your rear tires and lower the Jeep back to the ground. Be sure to tighten the lug nuts to specs (95ft lbs). Reconnect the negative cable, start up and check for leaks. Head to the gas station and fill up to your tanks true capacity for the first time!

Now, I'm sure you're wondering about the little ball valve on the end of the larger filler tube that you just cut off. As far as I know it's only purpose is to float up & cause enough back pressure to make the pump at the service station kick off after filling the tank to 15 gallons. IT IS NOT THE ROLLOVER VALVE, as some may believe. In the photo to the right, My Jeep was almost completely on it's side. I had a full tank, and not one drop spilled.

First things first, make sure you have a level solid surface to work on. Disconnect the negative battery cable for safety, and chok the front tires. I found it makes the job much easier if you jack up the rear end, place jackstands under the axle and remove both rear tires first, otherwise they'll just get in the way.
	Next step is to remove the eight screws holding the filler ring, cut the zip-tie holding the axle breather tube, and disconnect the ground strap.
Now it's time to disconnect the electrical connections, fuel and vent lines. There will be a small red plastic piece (pictured below) that holds to connectors together. The tab will have to be pushed to the left with a small screwdriver as the whole piece is pulled down. Remove the EVAP hose (the smaller one) by pulling and twisting (be careful not to bend the metal tube). Disconnect the fuel line by pinching the gray tabs together with your fingers and pulling the hose from the metal line. Watch for dripping fuel!
	Next place a jack under the gas tank and remove the 7 nuts holding the tank on the frame. Slowly lower it down while guiding the filler tubes around the frame.
You're going to need a wide flat-tipped screwdriver and a hammer to remove the large ring holding the pump in place. Place the screwdriver against one of the tabs & use the hammer to tap the ring loose COUNTER clockwise (opposite the direction the picture shows).
	Once the ring is out of the way, carefully pull the pump upward from the tank. Make a mental note of the orientation of the seal, this will make installing the new one a little easier.
Now for the fun part. If you reach inside the tank you will feel two filler tubes, one will be larger than the other. Take a razor blade on a scraper handle (pictured right), and rock it back and forth with firm pressure against each tube about one inch from the top of the tank. This will allow you to cut the filler tubes without having to worry about plastic pieces in the bottom of the tank. Take your time, as reaching into the tank may be awkward.
	Let's get that thing back together! Once the tubes are removed, install a new seal on the fuel pump (you did remember to get one before you started, right?) and carefully place the pump back into the tank. As you compress the pump assembly, make sure the seal is seating properly and not binding. Once in place, re-tighten the large ring by turning clockwise by hand. You should be able to tighten the ring without it wanting to "pop" off. If not, check the pump. It may not be seated properly, OR if you had installed an aftermarket tank skid, the straps may be too tight. Once the ring is on as tight as you can get by hand, use a same flat tipped screwdriver and hammer to turn it one quarter more turn.
Time to re-install the tank. At this point I recommend using at least two jacks (I used 3!) to raise the skid & tank back onto the Jeep. The reasoning behind this is that I've found the front bracket tends to hang up on the trackbar unless the skid is brought up at an angle. Before raising back up make sure all your hoses and electrical connector are where they need to be when it's time to connect them back up.
	Guide the filler tubes back through the frame as you raise the skid/tank back into place, raising the front of the skid up first to clear the track bar. Once the lip of the skid has cleared, raise the rear. Frequently check that none of the hoses or wires are catching on the frame. Once the skid is in place, re-install the 7 mounting nuts. Reconnect all fittings and re-install the filler ring.
Re-install your rear tires and lower the Jeep back to the ground. Be sure to tighten the lug nuts to specs (95ft lbs). Reconnect the negative cable, start up and check for leaks. Head to the gas station and fill up to your tanks true capacity for the first time!
	Now, I'm sure you're wondering about the little ball valve on the end of the larger filler tube that you just cut off. As far as I know it's only purpose is to float up & cause enough back pressure to make the pump at the service station kick off after filling the tank to 15 gallons. IT IS NOT THE ROLLOVER VALVE, as some may believe. In the photo to the right, My Jeep was almost completely on it's side. I had a full tank, and not one drop spilled.