Fuel pump... relay?

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Joe A
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Fuel pump... relay?

Post by Joe A »

The fuel pump on one of my LCs started making that rattling noise that it makes at startup all the time, and acting like it was experiencing fuel starvation.

My first thought was a fuel pump. It was also suggested to me that it might be the fuel pump relay, but according to the wiring diagram, there is no relay: the fuel pump is connected directly to the ignitor.

I found a replacement pump on ebay that is supposed to be 100% compatible: http://goo.gl/FYLmGD

It dropped right in - even the connector was the same - and it makes the same, although slightly louder, noise on startup. But, it also makes a loud click every few seconds while running. At high throttle settings, the click speeds up. It seems to run fine, but it does concern me a bit.

Anyone have any thoughts on this?

NE_FL
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Re: Fuel pump... relay?

Post by NE_FL »

Can you define "acting like it was experiencing fuel starvation?" Was it coughing, hesitating, missing, or what? And does it still do that with the replacement pump? You said that now "It seems to run fine".

I wouldn't be too concerned with the "clicking", that is just the pump maintaining fuel pressure. And I would think that the "rattling" noise on startup is the same, but it shouldn't be much different from the "clicking" noise.

Joe A
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Re: Fuel pump... relay?

Post by Joe A »

It was hesitating and missing with the old pump. As for the new pump; I just ran it at idle for a couple of minutes - the rear brakes still need some attention before I ride it.

As I understand it, the pump is designed to run for a few seconds when current is first applied at start up - hence the typical rattling sound when you first tun the key on these bikes - and then continuously when starting or running. I realize I'm in uncharted territory with this aftermarket pump, but I didn't have the $75-100 for a used one (and who knows if it's about to fail too), let alone the $200 for a new one.

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WintrSol
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Re: Fuel pump... relay?

Post by WintrSol »

The power is applied to the fuel pump and injectors by the fuel pump relay, so should run all the time the key is on. The initial clicking is probably the pump trying to get the fuel pressure up to 43psi; when that pressure is approached, I would expect it to get quieter. After the pump is the pressure regulator, which dumps fuel back to the tank to maintain the pressure. You could have a failing fuel pump relay causing the clicking after the system is pressurized by dropping out intermittently. Does the click happen at a regular rate, or is it kind of random? If random, that would be a failing relay, which could be what caused your pump to fail. If it is regular, that may be just how that pump works. Since you say it speeds up with more throttle, it could be either the relay responding to the higher vibrations, or just the pump pushing more fuel. The FP relay is shown as just to the rear of the injectors in the service manual, at the right side of the ECM.
Florissant, MO
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Joe A
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Re: Fuel pump... relay?

Post by Joe A »

Thanks, but mines an old carbureted '99.

I got an email back from the seller that the clicking noise is normal, but that it shouldn't be too loud. They asked for a video file to look/listen too. Pretty impressed with their service, so far!

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WintrSol
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Re: Fuel pump... relay?

Post by WintrSol »

Oh, OK, then yours is like the VS800 and VS1400, which is turned on with the starter button, and then shuts off when the carbs are full (as indicated by a small pressure rise). The pump relay in this case gets a signal from one of the coils, which triggers it and, if the pressure drops, the pump starts again, as long as the engine is running. In older models, the pump relay was separate, but was moved into the pump in later models; I don't have the data for the LC as to when this change was made.
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Joe A
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Re: Fuel pump... relay?

Post by Joe A »

Thanks, that confirms my understanding.

It also jibes with what the seller said:
Our fuel pumps really exist some noise due to special structure. This type pump works through continuous striking point. But it is abnormal if it is very loud.
I think "continuous striking point" is Engrish for "internal relay".

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WintrSol
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Re: Fuel pump... relay?

Post by WintrSol »

Gotta love data that's been translated through three different languages! :lmao:
Florissant, MO
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