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post #1 of Old 05-07-2012 Thread Starter
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another fuel lift pump question....

I have a Volvo MD17C.
For many years now, I have been running a pressurised fuel system, effectively presurising the fuel delivery from the tank to the Racor filter, then from there the fuel feed runs to the engine-mounted lift pump and engine-mounted fuel filter.
The system has been very reliable, and I have never drawn air, or had a problem. It draws about 2-3 amp, at nominal 12V.
One thing concerns me though : if the engine lift pump fails its diaphargm, then the electrical lift pump will fill the sump of the motor with diesel and I have no feedback until it is too late and my motor is full of diesel.
The electrical lift pump is intermittent, with a rub-dub-dub vibration every 2 or 3 seconds. If the engine lift pump diaphagm failed, the electrical lift pump would run continuously.
I had the idea of rigging a bulb in series with it and running the bulb to a wooden bulkhead in the footwell. That might work, but if I wire the bulb in series it will corrupt the 12 V voltage drop needed through the pump.
I had thought of a fibre-optic, but I don't know how to do that.
Effectively I need to light a bulb at the moment that the pump is running. And the bulb needs to go out when the pump stops.
Can I do that with a bulb in series? How would that work, unless the bulb was very low resistance.
An in-series ammeter would do, I suppose, and I just watch for the needle wavering. If it stays on, then I have a problem. That would work, I guess, but i will have to watch the ammeter all the time.
I really need something to warn me if the electrical lift pump stays running continuously, and stays quiet if it operates intermittently. That's a not an easy call for me to design.

What do you think folks?

Last edited by Rockter; 05-07-2012 at 09:46 AM.
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