fried fuel pump relay

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Posts: 6
Joined: Fri Jul 24, 2009 10:49 am
Location: Tonganoxie, Kansas
Motorcycle: 1984 Gl1200 Aspencade

fried fuel pump relay

Postby tongy66086 » Thu May 09, 2013 5:12 am

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Join Date: May 2009
Location: Tonganoxie, Kansas, USA
Posts: 20

fried fuel pump relay
Hello all,

This past winter, I pulled the engine out of my 84 Aspencade to put new clutches, replace a couple of gaskets and a clean up of the engine.
I finally got the engine back in, all wires, hoses, etc. hooked back up.
Last night, I thought I'd fire the engine up even though I still have the saddle bags, etc. to put back on.
I had been cranking on the starter for maybe 45 seconds when I heard a pop come from somewhere up front, and then a plume of horrible smelling smoke came rolling up from the coil area.
I was mad, to say the least, so I just walked away. Went out tonight and turned the ignition on, and just a few seconds later I got the column of smoke again. This time I could tell it wasn't coils, but from underneath.
I pulled the fuel pump relay off, and it nearly had a hole burned through the casing.
I have a donor bike, so I have another relay, but following the schematic in the book, I see the wiring for the relay goes to the coils, and another wire goes to the CDI, and after that, I quit following the diagram and thought I'd come post here, seeing as how I'm getting into some expensive parts to replace if I burn them up.
Anyway, does it seem like maybe the relay just went bad on it's own, or could something else be the culprit that burned the relay out?
Other than removing the fuel pump to pull the engine, I didn't remove anything else.
Has anyone else experienced this, and if so, what did you have to do to fix it?
Thank you so much for your help on this.

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Re: fried fuel pump relay

Postby virgilmobile » Thu May 09, 2013 9:37 am

I'll go from memory....
the 'relay' is a electronic switch....
it has 12 volts applied to it and has a 'sense' wire that monitors the ignition coil for a pulse.
at the moment it sees a coil pulse,the circuit ALLOWS current to flow to the awaiting pump.
this wire does not switch on 12 volts to the pump so when the pump is unhooked it will not show any volts on it.
It will only pass the 12 volts IF the pump needs it and at the moment there is a spark.

Now to your problem....It burnt up from 2 possibilities...
1..catastrophic component failure inside the module..Not likely
2..more likely...the wire that goes to the fuel pump is shorted to ground,or the pump is seized in the cycle position and drawing constant power

At this point the test procedures need to be specific...
1..unplug the pump "relay"..identify the wire that feeds the pump..
2..unhook or unplug the pump.
3.. measure for a short to ground on that wire....fix as needed.
4..if no short is found..suspect the pump is not cycling.
The pump is a pulse type...When 12 volts is applied,the coil draws a huge amount of power for a fraction of a second to operate it's plunger...If the pump is locked up,it can draw that huge amount of power and smoke the relay just as a shorted wire can.
Removing the rear cover off the pump reveals the switch and plunger can be manually operated....I did find a rubber dampening bumper inside one that could deteriorate and jam the pump.

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