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Where to check fuel pump amperage? 700

posted by alschnertz on Thu Sep 27 16:45 CST 2012
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last visit: Fri Oct 24 10:32 CST 2014

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1986 745T, 157,000 miles.

I found that the fuel pump fuse was getting very hot. Almost to the point of not being able to touch it. (I did have to change the fuse panel a few years back due to meltage).

The FAQ says that the main fuel pump should draw 6.5 amps.
Where would I check that? I connected my amp meter across the fuse and found it was drawing between 10.5 and 12.1 amps. Maybe that's a combination of the pre-pump + the main pump?

Seeing that high amperage, I elected to replace the main pump. So I put the new pump in and am still drawing 11.5 amps at idle.

Is it likely that the original pump was fine?
--
"Differences of opinions should be tolerated, but not if they're too different' - Sharon Craig

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Where to check fuel pump amperage? 700

posted by Art Benstein on Thu Sep 27 16:57 CST 2012
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last visit: Fri Oct 17 20:10 CST 2014

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That's where to check it, but I suppose you are getting both pumps in the reading. In any event, that sort of increase in current over spec is not, I repeat _not_ the reason you have burns and meltage. The increased resistance of oxidized and loosened crimps and spade lug contacts are what cause the 700 ash tray fuse panels to take up smoking.

Lucid gave me this idea -- made dealing with a fuse panel on a 940 easier. The ammeter was easy to insert using this extender cable.

One possible reason for slightly elevated pump current is a clogged fuel filter.
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Art Benstein near Baltimore

Growing old is mandatory; growing up is optional.

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Where to check fuel pump amperage? 700

posted by alschnertz on Thu Sep 27 17:14 CST 2012
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last visit: Fri Oct 24 10:32 CST 2014

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When I replaced the fuse panel a few years ago, I was very careful to clean and solder all the crimp connections. All were very clean to begin with. At that time, I also replaced the fuel pump relay and drilled cooling holes in the relay body too.

Additionally, at that time I also removed the fuel pump wires from the fuse panel and replaced them with a separate 30 amp fuse holder (though I only use a 20 amp fuse).

Fuel filter was changed 7K ago.

Thanks, but any other ideas?
--
"Differences of opinions should be tolerated, but not if they're too different' - Sharon Craig

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Where to check fuel pump amperage? 700

posted by Art Benstein on Thu Sep 27 17:54 CST 2012
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last visit: Fri Oct 17 20:10 CST 2014

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Well, looks like you may have to do it again, if you have heat rise within the fuse panel. There's no other explanation for it. Ohm's law isn't on the docket at the new supreme court.

The drilling of holes in the relay is another myth promulgated on the forums. The myth arises from the surprise at what temperatures can be achieved by continuously dissipating two watts confined in a couple cubic inches. Seems like a lot, but the materials are OK with it sans DIY ventilation. The heat comes from the coil.

--
Art Benstein near Baltimore

Forget the health food. I need all the preservatives I can get.

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