Fuel pump replacement and tank mod

Five

Five

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Jan 21, 2019
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North Carolina
I am about to replace my fuel pump (loses pressure and requires two tries of the switch before starting) and plan on trimming the vent line to allow the tank to fill to capacity. My question is, what is the difference between the fuel pump for 15 gallon tanks and 19 gallon tanks. My understanding is that they are the same tank with different vent lines. So, is the difference the sending unit for the fuel gauge?
 
What leads you to believe you have the 15 gallon tank? Most TJs came with the 19 gallon tank, only very stripped down models came with 15 gallon tanks. Going solely by the gas gauge can lead some to believe they have a 15 gallon tank when they really have the 19 gallon tank, the gas gauge is notoriously pessimistic. Even when my gauge indicates my tank is near empty I can still have 4-5 gallons remaining.
 
Yes the only difference is the fuel gauge itself, otherwise both assemblies are identical. The tank rated to 15 gallons can be easily modified by shortening the vent line.
 
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TJ4Jim said:
Yes the only difference is the fuel gauge itself, otherwise both assemblies are identical. The tank rated to 15 gallons can be easily modified by shortening the vent line.
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I guess I'm still unclear as to what this actually does if the tank still takes 19 gallons. Does it somehow allow the gauge to read a little bit more accurately or?
 
Vasq said:
I guess I'm still unclear as to what this actually does if the tank still takes 19 gallons. Does it somehow allow the gauge to read a little bit more accurately or?
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By shortening the vent line, It allows the tank to fill completely before kicking off the gas pump handle.
 
Vasq said:
so even though I have a 19 gal tank, I'm never actually fitting 19 gallons in it?
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You may be, but I am not. The 15 and 19 are the same tank with a different length vent line extending into the tank. This causes the gas pump to sense pressure at ~15 gallons and shut off rather then filling to the 19 gallon capacity.
 
interesting. is there any downside to snipping it? or potential of overfilling or something like that?
 
No
Vasq said:
interesting. is there any downside to snipping it? or potential of overfilling or something like that?
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Not that I can find. There are threads about this mod all over. My Ford diesel truck is the same. On Fords, it’s called the “harpoon mod”
 
jeepins said:
So the 15 and 19 gal tanks are exactly the same size? What in the hell is the rationale behind that exactly?
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I imagine the rationale was that some bean counter at Chrysler decided that they could charge more for the "bigger" tank.

My question is this: Is there any mod out there to make the gauge more accurate? I regularly run mine past E and still never put more than 17 gal. in it. One of these times I'm going to push it too far though. Then again, I guess that's what jerry cans are for.
 
I would do a say 3-tank average and see what you can run it to.. maybe even have a can with you and run it empty just to see what normal driving will get you. Then reset your trip meter everytime you fill up.
 
Yeah that's what I do. I'm comfortable taking her to about 235 miles on a tank. But one of these times I will forget that I was idling for a long time or something else has negatively impacted my fuel economy (lol) and I'll end up out.

I was just looking to see if there was an updated sending unit or something that improved accuracy of the gauge.
 
Jeep made much more money on the premium packages like the 4.0 Sahara and Sport. On the showroom floor crippling the tank on the SE leveled the playing field a bit with respect to range and gave people one less reason to buy the cheap Jeep. You don't want your base model to have too many things better than your premium package. If people were worried about the mileage when deciding it was easy just to fall back on the larger tank making up for the mileage difference.

Adam Johnson said:
I regularly run mine past E and still never put more than 17 gal. in it.
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What does "run past E" mean to you exactly on the gauge?
 
pagrey said:
Jeep made much more money on the premium packages like the 4.0 Sahara and Sport. On the showroom floor crippling the tank on the SE leveled the playing field a bit with respect to range and gave people one less reason to buy the cheap Jeep. You don't want your base model to have too many things better than your premium package. If people were worried about the mileage when deciding it was easy just to fall back on the larger tank making up for the mileage difference.


What does "run past E" mean to you exactly on the gauge?
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To the point where the needle is fully to the left of the letter E on the gauge. Not quite to the place where it rests when the ignition is off.
 
Be careful running it completely empty. I wouldn't as it's not good for the pump, and you can sometimes pick up crud that is laying in the very bottom of the tank.
 
Here's a quick photo of mine at rest with the ignition off. The needle will move to the left of this position and no longer touch the white on the letter E when it is bone dry. It moves under power left of the at rest position. Does your needle rest off the E with the ignition off? When I perform the self test my gauge stops just at the left end of the red where it is supposed to so I don't think it's off. I have replaced my sending unit and it reads exactly the same. You might try that. Just curious, I know it's just a gas gauge and not a big deal, just entertaining to me.

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Your pump draws from the bottom of the tank. If there is crud in your tank you are constantly sucking on it with those screens no matter what the fuel level is. No fuel also means the engine stops and when the engine stops the pump stops. Not any real risk running it dry as far as I see it but obviously do what you feel safe doing.
 
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