Problem with fuse that becomes hot
 

Dear all,

I have a question the fuse number 16 (fuel pump for an 911SC 78) in the luggage compartiment becomes very hot (wire of the fuse), after several times when i drove the car the fuse becomes defective, i did a measurement of the current between pin 30 and 87a of the fuel pump relay (relay removed) and measure 10,29A. Is this current not to high and have i a defective fuel pump.

Regards,

Peter

same thing happened to me. its the actual fuse block in that specific location. the metal, over the years developes an amount of resisitance, hence the heat build up and eventual failure. what i did was move the fuel pump fuse to a location that is reserved for the sunroof, that i dont have, and everything is ok so far.

Clean up all the contacts first. Corrosion anywhere between the fuse's positive supply and the fuel pumps ground will cause inline resistance. In turn, causing the pump to pull more power across the circuit than intended which will generate heat. The relay contacts, fuse contacts, and fuse block wire contacts are the easiest to access so I suggest starting there.

After you clean it off, if it still gets hot, your fuel pump could be on its way out.

Unscrew the wires going to/from the fuse holder and look at the end of the wires. If they are green or black inside, not copper colored you will have increased resistance in those wires.

The resistance will make the wires heat up and sometimes even melt!

You can probably cut away 1/2" to 1" of the wires to get to good conductive wire and still reach the screw terminals.

I cut ALL my wires 4" back and soldered in new wires when I converted to flat style fuses. On some of them I found corrosion as far as 3" from the ends!

Use sand paper to clean the mounting points of the fuse.

Pull the relay and use a knife at the end of each pin to make it wider. This will ensure good contact in the relay socket.

Good luck :)

What a timely post! This "hot fuse" problem happened to me just last night on the way home from a date! Fuel pump fuse over-heated and melted the solder inside the fuse (glass tube type) at one end to break the electrical connection. I'll have to check all the ends of my wires. She was impressed that the problem was found and we were back on the road in about four minutes. :-)

Thanks!

The factory spec -- max allowable drain for a CIS fuel pump is 8.0 Amps ... so, that pump is definitely out of spec!

Did you hear about the guy who used a .22 bullet in place of a fuse that had blown?

http://www.snopes.com/autos/techno/fuse.asp

That's a funny story :D

More suggestions for fuse replacement here: http://www.landroverclub.net/Club/HTML/humour_electrics.htm

I actually saw on the Discovery Channel on the show Mythbusters, they actually reproduced that story of the .22 bullet for a fuse. It actually fired the bullet when they created a short across it. They had a test dummy sitting in the drivers seat and a few of the bullets they tried hit the dummy in the shins. Probably won't kill you, but might be enough to cause a crash if it distracted you enough. It was pretty crazy stuff.

Timothy

a comtender for the darwin awards.

Does a .38 have a higher current rating? I like to have a variety of fuse backups.

Sherwood

Sure, Sherwood - then you might be able to win a JBS Haldane award.

Sitting with the pump running without the engine started or blockage in the lines will cause excessive current draw. This tends to overheat the pump because they are gasoline cooled and require the fuel to flow to cool the pump.

" then you might be able to win a JBS Haldane award."

Randy,
Please enlighten me or lower that thought that just went over my head. What is the JBS Haldane award?

Sherwood