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Unread 10-09-2009, 02:47 PM   #1
bandanaboyz
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5.9L Grand Cherokee Fuel Pump Issue

Here is my situation:

I own a 1998 5.9L GC. I have noticed that duirng the past month when I fill up my tank I am short by 6 gallons. Now, my inside guage reads full but my gas tank is not. I have no problem starting the car or driving it. Is this a sending unit issue or is the fuel pump the likely problem? The sending unit part is $55 and an aftermarket fuel pump is about $300.

What should I do? If need be, which fuel pump would you purchase, dealer or aftermarket? Which aftermarket?

TJS

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Unread 10-09-2009, 06:32 PM   #2
Kolak
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Are you saying that the gas pump shuts off before the tank is full? And that you can't top it off because the nozzle keeps shutting off? If that's the case I would suspect a problem with the tank venting/evap system.

Quote:
Originally Posted by bandanaboyz View Post
Here is my situation:

I own a 1998 5.9L GC. I have noticed that duirng the past month when I fill up my tank I am short by 6 gallons. Now, my inside guage reads full but my gas tank is not. I have no problem starting the car or driving it. Is this a sending unit issue or is the fuel pump the likely problem? The sending unit part is $55 and an aftermarket fuel pump is about $300.

What should I do? If need be, which fuel pump would you purchase, dealer or aftermarket? Which aftermarket?

TJS
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Unread 10-10-2009, 09:53 AM   #3
bandanaboyz
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Kolak, yes that is correct. However, the fuel guage on the instrument cluster reads full. Normally the Jeep takes between 80 & 88 litres of gas. Now it only takes 60 to 65 litres of gas from empty. When I say empty, I mean when the empty light comes on and I am down to my last 20km of travel on my computer.

How do I test the tank venting/evap system?
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Unread 10-10-2009, 01:38 PM   #4
CULate
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Quote:
Originally Posted by bandanaboyz View Post
Kolak, yes that is correct. However, the fuel guage on the instrument cluster reads full. Normally the Jeep takes between 80 & 88 litres of gas. Now it only takes 60 to 65 litres of gas from empty. When I say empty, I mean when the empty light comes on and I am down to my last 20km of travel on my computer.

How do I test the tank venting/evap system?
My question is how do you know the tank isn't FULL? Because it doesn't take what it use too. The vent should be a closed circuit vent system for smog reasons. I believe there is a small hose that goes up to the filler neck. Getting to anything tank wise is a bear. But you could disconnect it & see. I helped put a fuel pump in a WJ & things are really hard to get to without dropping the tank down. If they have a receiver hitch it is even worse. Good Luck.
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Unread 10-10-2009, 01:57 PM   #5
MiniTubbedNova
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the pumps shut off because of the back flow of gas not air... let it fill to stop, wait about 20 seconds and try it agian if it pops immedatily then its full. sometimes with faster puming stations the anti syphon valve causes the pump to stop. or your sender could be bent. how long does it stay on full for.
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Unread 10-10-2009, 04:31 PM   #6
bandanaboyz
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It does not stay on full very long. I have waited the 20+seconds and the tank only wants to hold about 65L of gas when it normally takes 85L to fill.

How would the sending unit bend?
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Unread 10-10-2009, 04:43 PM   #7
MiniTubbedNova
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i dont know how the sending units look in a grand, but older cars have basicly a coat hanger with a float on the end, so in essance you could have more gas than you think. but that would be unlikely.
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Unread 10-10-2009, 04:54 PM   #8
Kolak
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Now that I think about it, if the gauge reads "full" when the tank is not, it's probably reading empty when it's not quite empty either. So when you go to fill up, you're not able to add as much fuel as per usual because the tank isn't really empty.

As you mentioned in your earlier post, you can just replace the sending unit. That involves dropping the tank and removing the pump. So given all that, it may be wise just to replace the complete pump module given that you probably have a lot of miles on your Jeep and it's a fairly big job to do.

A complete pump module comes with the pump, filter assembly, and the sending/level assembly, all integrated together.

PM me if you'd like pricing - I sell genuine Mopar replacement parts to JeepForum members at 25% off what you'd pay at the dealership.
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