Fuel pump not running

Joined
Jul 28, 2007
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3,118
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finger lakes ny
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1999 ST1100
STOC #
7959
Fuel pump isn't running on my 91. (via ignition, which is fine). Pump runs fine when jumped directly to the battery.
What and where to look ??
 
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Uncle Phil

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Dean - I would check that the relay is getting power, then 'jump' around it and see if the pump runs. If the relay is getting power and none is coming out, that pretty much points to the relay. A simple test light should help you sort it out.
 
Joined
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soCal
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687
Hey Dean, another guy was tracing out that problem over on the other ST forum a month or two ago, take a look for that thread for a reference. Bottom line is that relay is a Honda specific ($50 or so) part, so you can't just swap a simple automotive mechanical relay in its place. Its a solid-state relay (SCR) that's controlled by the ignition module so I'd pull it from the socket and jumper across the switched pins in the socket and see if your pump starts working. After I post this I'll look for the other thread and try to post a link.

Here's the link:

http://www.st-riders.net/index.php?topic=11716.0

BTW, in his case the problem was apparently a plugged breather in the gas cap, and not the relay, see the last post. May be something else to check while you're at it.

Also, because its a solid-state relay, don't bother trying to test it out of the socket, not sure how durable it is. The normal energizing signal is from the ignition module, which is likely a low current source. Not sure if putting 12v direct across the energizing pins would drive more current than it was designed to handle, so I'd avoid it for now.
 
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8901
I have the 90-95 wiring diagram. Fuse D powers the ignition, and the fuel pump. For power to reach the pump, after the fuse it it has to pass through the lean angle relay, which feeds to the kill switch and from there to the fuel cut relay.

As UP suggests, check for power at the fuel cut relay, and work back up the supply line. Of course the pump won't run with the kill switch off, and it will only run for a few seconds when you first turn the ignition on, and won't run continually until the engine is running.
 
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DeanR
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Jul 28, 2007
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finger lakes ny
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1999 ST1100
STOC #
7959
Thanks for that link Doug. I'll try what is suggested. (hopefully) . I do ok with mechanical stuff, but that electron stuff and lingo just completely goes through my head. I need basic how to's on what to connect to what.
 
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DeanR
Joined
Jul 28, 2007
Messages
3,118
Location
finger lakes ny
Bike
1999 ST1100
STOC #
7959
I have the 90-95 wiring diagram. Fuse D powers the ignition, and the fuel pump. For power to reach the pump, after the fuse it it has to pass through the lean angle relay, which feeds to the kill switch and from there to the fuel cut relay.

As UP suggests, check for power at the fuel cut relay, and work back up the supply line. Of course the pump won't run with the kill switch off, and it will only run for a few seconds when you first turn the ignition on, and won't run continually until the engine is running.
Thanks for deciphering the wiring diagram Terry.

Yea, I don't get that couple seconds of the fuel pump running as the ignition is turned on.
 
Joined
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soCal
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'97 ST1100
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687
Thanks for that link Doug. I'll try what is suggested. (hopefully) . I do ok with mechanical stuff, but that electron stuff and lingo just completely goes through my head. I need basic how to's on what to connect to what.
The wire colors are called out in the link provided. There's two wires/pins for energizing the relay, and two wires/pins to switch the power to the pump. If you jumper the two pins in the socket to effectively bypass the relay and power the pump directly, you should have 12v at the pump. First thing to check is that you have 12v at the socket before bothering to put the jumper wire in. As Terry mentioned, there's other things in the path that could be causing the failure. So either start at the pump and work your way backwards, or start at the fuse and work forward.

If not sure about the exact procedures, ask questions first, its not too difficult once you get access to the relays.
 
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Out of interest I worked through the entire map from battery to fuel pump which looks like:

Battery + ---30A fuse@starter relay ---red wire ---ignition switch ---red/black wire --- Fuse D ---black wire ---engine stop relay (switched) --- black/yellow wire ---engine stop switch --- black/white wire --- Fuel cut relay (switched) --- brown/red wire --- fuel pump --- green wire --- Battery -

and ....Fuse D --- black wire --- Engine stop sensor (tip switch) --- red/white wire ---Engine stop relay switching side --- green wire

and ...engine stop switch --- black/white wire --- ECM --- blue/yellow wire --- fuel cut relay switching side --- green wire

Time to get your multimeter out (or at least a test light).
 
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