Fuel Pump

I guess its time to learn about the fuel system.

I was welding on the rear passenger side floor of my 1996 XJ (the fuel tank was still in, bad idea maybe?.) Now when I run it I seem to have a problem with my fuel pump. It all works fine but it makes an awful electrical buzzing sound. The buzzing comes from the component which runs for a second when you move the key from "on" to "run." Then it continues to buzz after I turn the engine over. I assume this is the fuel pump.

All the wires/tubes going to the bung on the front of the tank are fine. However there is a small tube going over the top of the tank in the vicinity where I was welding. Is this just a vent line, and is there anyway this could contribute to my problem?

Stupid question: After the sytem is presurized does the pump or whatever constantly run? Or is it intermitted and what I'm noticing is the fact that is always on, not necessarily louder then it was before?

Any insight would be appreciated.

Thanks,

Matt

First I hope you disconnected your negative terminal before you started welding. I hear you can damage the computer and other electrical components. What year is your XJ. My 90 has a resistor on the drivers side fire wall (a white block about 1 1/2 to 2" long, with a wire coming out each side of it). It allows full voltage through to the fuel pump when starting and then kicks back to quiet the pump down. I guess the resistor was added because of the noise from the fuel pump. It sounds like it is receiving full voltage constantly, could lead to premature failure. What year is your Jeep?

That buzzing sounds just like a worn-out fuel pump. Does the pitch or loudness change when your tank is full? A full tank of gas will sometimes muffle it a little. As far as when it runs - it runs for a few seconds before you crank, then shuts off, then once you're running it is continuous again. A noisy fuel pump can stay working for a long time, but it's probably a good idea to keep your eye on it and schedule a new one.

Remember that on a closed system like this one "just a vent line" should be leading somewhere, and not open to the outside world, so check carefully if you think one is damaged.

Thanks for the input. I did disconnect the negative terminal. Do you know what resistance that resistor should be? I'll do a search and try to find out.

The vent line does join up with the the other fuel lines. I'm thinking if I damaged the vent line while welding I probably would have noticed :explosion

As for the pitch changing, right now the tank is pretty full. I guess I'll take a trip to the stealership on Monday and see what a new one costs.

I found the resistor value, but is this resistor an "all makes all model" sort of thing? I've got a 96 with the MPI system not TPI, so far no resistor.

Matt