the fuel pump whirrrrr is backwards!

[brentandlorie]

I've tried replacing the fuel relay and fuse to no avail. The fuel pump is constantly getting juice? I only hear the fuel pump whirrrr when I shut the truck off? Truck starts and runs fine, but of course the battery is being slowly drained because of this?

any electrical engineers out there have any clue?

 

[Tbars4]

...this would be useful info in your other thread as those who read it could follow the progress of this problem...
http://www.explorerforum.com/forums/showthread.php?t=205821

 

[MrShorty]

Does the pump stop if you pull the fuse? relay? unplug inertia switch? The fuel pump circuit is a pretty basic DC circuit, shouldn't require an EE degree to diagnose it. You just need to figure out why the relay is sticking closed, or where the short to power is.

 

[brentandlorie]

see, thats the thing. The pump only runs ( whirrrs) when i shut her off. It only lasts a few seconds.....

 

[DeRocha]

see, thats the thing. The pump only runs ( whirrrs) when i shut her off. It only lasts a few seconds.....

You only hear the fuel pump for a few seconds after the engine is shut off? To confirm the pump is no longer getting power check the fuel pump inertial switch located below the glove box. Pull back the carpet behind the glove box and find the fuel pump inertia switch (pictured below). Use a meter (or test light if thats all you have) and connect either wire of the switch to HOT, and then ground the meter to a suitable ground. The meter should read 12v when the fuel pump is running and ~7v when its not.

As you may already know the fuel pump will only run when given 12v... When you turn the key from run to start the inertia switch (pictured below) will see 12v for only 2 secs or while the tac registers > 0 RPM. After 2 secs of zero RPM the computer will shut off the fuel pump relay and you'll only see ~7v at the inertia switch and fuel pump. Seeing 7v is weird but that is what you'll get if you check the wiring.

 

[brentandlorie]

Thanks DeRoche. I'll check it out tonight after work.

btw..battery dead this am, cgarging back up now! AARRGGHHHH!

 

[brentandlorie]

All the electrical testing advice i received was great and all signs pointed back to a bad relay after all! Bought another one from autozone and bingo......relay activates the pump when i turn the key on, and not when i shut her off. The one I replaced a month or so back was bought at schucks auto parts. I guess that's what i get for "assuming" a new part would work.

That isn't the first bad elecrtical part I got from schucks, but it will be the last!

Thanks to everyone.

 

[DeRocha]

Glad to hear you solved the mystery