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Fuel Pump voltage? New guy.

Posted: Tue Feb 22, 2011 9:36 pm
by UberWagen
I thought I posted this question, but I guess it didn't go through? Anyway, I'm assisting an older couple in the neighborhood with their '81 528i. No start situation. I pulled the CSV, grounded it out, no fuel. I misdiagnosed the problem as being a combo relay at first. I then proceeded to doing the AFM door propped open, turn on the ignition switch and see if you get a fuel pump buzz deal. I checked voltage back at the pump to see what I was getting. I got 8 volts to the connectors on the fuel pump. No noise in the pump at all. I would assume the pump runs off of 12V. But wouldn't 8V carry enough current to at least make it hum a little? Any input is highly appreciated!

Posted: Tue Feb 22, 2011 10:33 pm
by Mike W.
I think 9V is usually considered the cutoff number for things working. But still, I would expect it to at least try to run on 8 being a DC motor and all. But unless the battery is really, really low, I would look first to why it's only 8V? Unless, now this is a long shot and the fuse should blow I would think, unless the pump is seized and drawing so much current that you are getting voltage drop. Remove a lead and see what voltage you get.