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empty tank = no fuel pump worky?

bretto

NAXJA Forum User
Location
Orem,Utah
If your tank is bone dry does that cause the fuel pump to "shut off"? I got a ZJ I am looking at and the guage is on E. Normally you can hear the pump run momentarily to pressurize the system. We put in what gas we had in the tank which amounted to nothing but maybe .25 gallons. There is nothing I can hear and there is no fuel at the fuel rail schrader valve. I hoping it is just that there is not enough gas in the tank but it concerns me that I can't hear the pump.
Brett
 
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jayuu said:
i think ive heard if you run it bone dry you can damage the pump, but im not sure. add more gas and see what happens.

Yeah that is what we are doing tonight....I was just curious if someone might know b4 hand.
 
Your fuel pump is most likely dead. If you don't here it prime and don't have fuel pressure at the rail. Check the fuses and relays first though!

As for a automatic shut off if the tank is bone dry...I have never heard of that.
 
Gas cools the pump, it pumps from the time you turn it on till you turn it off, the constant cycling thru the return valve keeps it cool. You can run a tank dry once, maybe twice and get away with it, but each time you do you overheat it.
You will hear it prime then turn off but thats because it has pressure, once the engine starts and fuel starts being used the pump pretty much stays on.
 
i ran my tank dry once and it cost me the pump...
 
Gas also lubricates the pump rotors as well as cools it, so running a pump without the gas will burn up the pump. Gasoline is just very lightweight oil.

Don't rule out the PCM control of the Fuel Pump. The controls on the fuel pump are designed to prevent the electric pump from spraying gas everywhere after an accident.

*The pump will not run if there is no engine rpm, the PCM cuts off the fuel pump if it sense no engine rpm. To start the motor (since there is no RPM at first) the PCM will activate the fuel pump for 2 secounds right after turning the key on to build fuel pressure up in the system, but shut it off until the PCM senses engine RPM.

*Roll over valves and vents, there are controls on the fuel pump and gas tank to prevent fuel from spilling all over if the vehicle rolls over, there are vents and lines on the top of the tank for this. I'm not sure how the system works, but its possible that a bone dry tank could trigger something to kill the fuel pump, thinking its a roll over tank.

*Trapped fuel, the pump runs dry with a little bit of gas still in the tank, slosh, gap between the pick-up and the bottom of the tank, etc. When I changed out a fuel pump in my mini-van, I had to drop the tank, which I drained bone dry. It took 4 gallons of fuel poured in the tank before I got the motor to start, so your 1/4 of gallon is probably nowhere near whats needed to get gas pumping again.

*Noise, the pump probably makes a very different noise pumping air and gasoline. So just because you hear no noise, doesn't mean the pump is not working.

I'd check these all out before I spent a lot of money on a new fuel pump, it could be possible your pump is fine.

Get a voltmeter and check voltage at the plug from the car, if there is no voltage coming from the car, than most likely its one of those safety features above that is purposededly cutting off the fuel pump. If you do have voltage and you have 5 gallons or more of gas in the tank, but no fuel flow with the motor cranking, then I would suspect a bad fuel pump.
 
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