[imjrk]

Having a problem that we think may be fuel pump. Am finding that there are two different fuel pumps, brass fitting and plastic fitting. Are they interchangable? If not, any way to know which one I have before I pull it out of the tank? Problem we are having is a stumble at idle and low speeds. The engine will stumble, alt guage will jump down then back up, and fuel pump whine will change pitch momentarily.
Have changed fuel filter, plugs, wires, etc. Thanks

[Blade10]

Most problems with the fuel pump show themselves at WOT or while driving where the pump is not able to deliver the fuel. Based on your description it almost sounds like you have a power problem.

What is the fuel pressure when having the problem? When not having the problem? Do you have UPs installed? (If so temporarily ditch them for stock pullies and see if the problem goes away - if so you might have an alternator that is starting to crap out.)

Blade

[imjrk]

I have UDP's on it, but the problem just began within the last month and they have been on since spring. I cannot go back to stock pulleys, the crank pulley is bent. I swapped the alt. with the one in my six, problem persists in 5.0, no problem in the six. I have not checked the pressure, any advice on how I would do this?