Fuel tank filler tube mod to convert 15 gallon tank to 19 gallon

I believe what makes this happen is that the pressure differential in the tank is changed. When the gasoline level approaches the vent tube, the pressure is changed inside the tank, which then creates backpressure to the gasoline pump handle and shuts it off. By shortening the tube it allows more fuel in before the pressure builds and shuts the flow off. I maybe wrong, but I think this is how it works. Maybe someone more knowledgeable will pipe in.
 
  • Like
Reactions: Paparock1
I believe what makes this happen is that the pressure differential in the tank is changed. When the gasoline level approaches the vent tube, the pressure is changed inside the tank, which then creates backpressure to the gasoline pump handle and shuts it off. By shortening the tube it allows more fuel in before the pressure builds and shuts the flow off. I maybe wrong, but I think this is how it works. Maybe someone more knowledgeable will pipe in.
This explanation makes sense to me. There were quite a few posts on this modification several years ago. I did not notice any clear explanation like this one. But several different people clearly reported cutting off only the vent tube, and then getting 19 gallons of gas into their former 15-gallon tanks. So it works.
 
Does using the 19 gallon level sending unit require any changes to the dash gauge to work correctly????
Of all the earlier posts on this, on the Wrangler forum before this Wrangler TJ forum came into existence, and on the Jeep forum before the Wrangler forum came into existence, no one that I read reported needing any change to the dash gauge to work correctly.
 
I think my sending unit is messed up because when my gauge get close to the red area at the bottom, it just drops to E. I see this tank mod in my future now. Thanks DER52
 
Ive been having trouble with my fuel gauge showing 3/4 when i fill up. I'll also go 75+ miles after the gas light comes on. I was thinking that i possibly had a 19 gal fuel pump in my 15 gal tank. My pump went out this week and i saw it as an opportunity to fix the wacky gauge issue. After putting in a 15 gal pump in my 15 gal tank and running to the station it still only showed 3/4 full after a fill up. After seeing this thread its good to know that the tanks are the same size. Seeing this mod im thinking it may fix the gauge. It still doesnt explain why my new 15 gal pump doesnt show full with 15 gals in the tank but regardless an extra few gals in the tank would be nice. Ill try out the mod this weekend and give you all an update.
 
Now that I have seen the inside of a stock 19-gallon tank, thanks to my wife taking a picture of it for me (posted here above), I would not cut off the vent tube of the so-called 15-gallon tank nearly flush with the inside of the tank, like pictured in my first post here. Since the vent tube in the stock 19-gallon tank extends in about an inch, I would leave about an inch when doing the modification to the so-called 15-gallon tank. I do not know if this makes any difference, but what is in the stock 19-gallon tank at least gives us something to go by.
 
  • Like
Reactions: KCsTJ
Ive been having trouble with my fuel gauge showing 3/4 when i fill up. I'll also go 75+ miles after the gas light comes on. I was thinking that i possibly had a 19 gal fuel pump in my 15 gal tank. My pump went out this week and i saw it as an opportunity to fix the wacky gauge issue. After putting in a 15 gal pump in my 15 gal tank and running to the station it still only showed 3/4 full after a fill up. After seeing this thread its good to know that the tanks are the same size. Seeing this mod im thinking it may fix the gauge. It still doesnt explain why my new 15 gal pump doesnt show full with 15 gals in the tank but regardless an extra few gals in the tank would be nice. Ill try out the mod this weekend and give you all an update.
Adam, my gas gauge did the same thing that you describe. I have not put mine back together yet, so I do not know if it is fixed. Possibly it is a different issue, though.

But your profile says that you have a 1999 Sport 4.0. These all came with the 19-gallon tank standard. So you do not need to do any modification. The issue you describe must be due to something else.
 
As a point of reference. I received the build sheet of my mid 1999 TJ build. It shows a reasonable optioned Sport, automatic, 4.0 6 cylinder, A/C, am/fm cassette, with driver and passenger flip seats and back seat. The build sheet shows 15.3 gallon fuel tank. I can never get over 10.8 gallon in the tank down when the empty light comes on. Which I now understand is just the built in "reserve" if you think of it that way. I am going to do the filler tube modification next weekend. I'll post how it goes, but I think this post has been beat to death, but I did want to comment on the comment that only 4 cylinder SE jeeps after 1998 had 15.3 gallon tanks.
 
Der52 has done some great work here. But we aren’t done. I watched the video on converting the 15 gal to 19 gal on a YJ. But in looking at my 1999 TJ, it is like DER52 pictures and has the 15 gal tank part number, even though 1999 with air, radio cassette and others options, but on to the issue. I took off the vent hose on MT tank and I am sure there is not a hose within a hose like videos show on the YJ conversion. I messed mine up pretty good and it is just one tube that is part of that molded piece that has filler tube and vent tube. Have I missed a post, or is the only way to cut the vent tube is to drop the tank, remove the pump and go in through that hole to cut the tube from the inside? Any help appreciated. Has anyone shortened the vent tube from the outside on a TJ? Has anyone seen a tank on a tJ that has a tube inside the molded Tube that the vent hose clamps too? My tank is an 8687AB part number.
 
Adam, my gas gauge did the same thing that you describe. I have not put mine back together yet, so I do not know if it is fixed. Possibly it is a different issue, though.

But your profile says that you have a 1999 Sport 4.0. These all came with the 19-gallon tank standard. So you do not need to do any modification. The issue you describe must be due to something else.


Hmmm, I have a 99 Sport 4.0 and when I first got it, I did an "instavin" check on it. This is what it say's about the Jeep.

Jeep screenshot.jpg



I don't have the owners manual or the window sticker, so I can't say if the "instavin" search is right, but it's the only thing I can go by. I can say that I have gone down to almost the E before and it once took a little over 14 gals. One other time it took 15 and some change gallons, but can't remember exactly how much over the 15 it was. So either the vin check is wrong and I have a 19 gal tank, or there is a couple gals, before it actually runs out of gas, once you get close to the E!
 
Let’s put this to bed once and for all. Not all 1999 4.0L sports have 19 gallon fuel tanks! Mine has a build sheet that says it is a 15 gallon and the part number on the tank has been confirmed by Jeep as a 15 gallon. My Jeep came with upgraded stereo, sound bar, air conditioning and a couple other options I don’t know. There are 1999 4.0L Sports with 15 gallon tanks straight from the factory. Jeff
 
All these debates are easy to solve. If the last 6 digits on the tank part number are 8687AB, it is a 15 gallon tank. (Well 19 with a long vent tube so it only holds 15). The Part number is easy to read and I verified it with Jeep. I believe DER52 also confirmed it. Part number is on the Drivers side on the side of the tank. Just look under the fender on drivers side. It is right there.
 
  • Like
Reactions: Jerry Bransford
I suspect the factory just kept installing the 15 gallon tanks until they ran out in 99 as there are quite a few out there including mine. I highly doubt the last 98 off the assembly line used the last 15 gallon tank on the pile.
 
  • Like
Reactions: KCsTJ
KCsTJ seems to have cut the tube. But you say you dropped the tank. Did you cut it from the inside KCsTJ? If not please share!
Yes, I dropped the tank after running it low. I used a common utility knife and reached thru the fuel pump opening and carefully cut the plastic tube.
You really need to empty the tank for safety and weight reasons before cutting the tube.
Cut as close as you can, use a new knife blade and remove 3" or so. Reinstall everything and done.👍
 
  • Like
Reactions: JLANEF