Electric fuel pump permanently running

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MagicWagon
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Electric fuel pump permanently running

Post by MagicWagon »

Gradually going through the list of issues I want to address on my "new" camper. (83 Aircooled devon)
A PO has replaced the mechanical fuel pump with an electric one, and it is very noisy.
As soon as I turn the key (before I start the engine) the pump runs and keeps running.
It also keeps running when I turn the engine off. This doesn't seem right to me.
Should it run before I start the engine, or only when the engine is running ? and should it stop when I turn the engine off ?
If so, is it likely a faulty pump, or more likely wired wrongly.
Thanks.
1983 2.0L Air Cooled Devon Moonraker

Da dan
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Re: Electric fuel pump permanently running

Post by Da dan »

My one turns on with the key so I can prime it before starting. Then goes off with the key. It’s supposed to be wired to the alternator I believe. Where have you wired it to? Also have you put the rubber plate/ washer behind the pump to stop it vibrating?


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MagicWagon
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Re: Electric fuel pump permanently running

Post by MagicWagon »

I haven't had a chance to trace the cabling yet. When you say "My one goes on with the key.... then goes off with the key", do you mean with the key turned to the first position but engine not running ?
If so, that's the same as mine, which is not ideal as it means it keeps running if you stop the engine but just want the ignition left on (so other ignition-linked things to work - e.g listen to radio). Not only is it noisy but I think would exhaust the battery quite quickly.
I wonder how this pump or circuitry differs from my Triumph stag ? On that when I turn the key to the first position, the pump clicks several times to fill the carb float chambers but then stops by itself until you start the engine.
Maybe I need to add a changeover relay as per this circuit diagram ? Wont be able to do that until I work out why my ignition light doesn't work though.
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937carrera
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Re: Electric fuel pump permanently running

Post by 937carrera »

Couple of things going on here I think

Firstly change the wiring so the fuel pump only runs when cranking (ignition switch) or the engine is running (alternator output). That's just a safety thing so the pump switches off if you have an accident and are unable to switch the engine off. Look in the wiki.
Secondly, change the wiring so that your accessories are permanent live, rather than switched live.

If you have a leisure battery, then there is an easy mod for later fuse boxes to provide power to fuse 3 from the leisure battery. The same can be done with the early fuse box, I think it's fuse 6 or 8 you need to use https://vwt25.blog/2016/05/19/rewiring- ... e-battery/ for the fuse 3 mod

Additional benefit of that is you are not providing power to the coil and potentially damaging that when you want to listen to the radio.
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ajsimmo
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Re: Electric fuel pump permanently running

Post by ajsimmo »

Just wire it through a safety relay with 1.5sec prime function HERE
(Although carbs shouldn't need the prime as they'll already be full of fuel - this is designed for LPG but works very well for this application)
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CJH
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Re: Electric fuel pump permanently running

Post by CJH »

ajsimmo wrote:Just wire it through a safety relay with 1.5sec prime function HERE

Assuming that the 'pulsed signal' referred to in that link is from the coil, is this what's known as a 'tachometric' relay? I fitted a similar relay (thread here), as it seemed like the safest way to kill the pump in the event of an accident, e.g. if I was incapacitated and unable to turn the key, the pump would stop as soon as the engine stopped.

The relay I fitted runs for about half a second to a second when I turn the key, so if the van's stood for a long time I just turn the key a couple of times before attempting to start, just to make sure the carb is full.
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MagicWagon
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Re: Electric fuel pump permanently running

Post by MagicWagon »

Thanks for that ajsimmo
I'm having a job finding a circuit diagram or instructions of how I would wire up such a relay - i.e what connects to each connector.
Are you able to shed any light on it ?
Many thanks.
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Re: Electric fuel pump permanently running

Post by ajsimmo »

MagicWagon wrote:Thanks for that ajsimmo
I'm having a job finding a circuit diagram or instructions of how I would wire up such a relay - i.e what connects to each connector.
Are you able to shed any light on it ?
Many thanks.
Image
Ignition live (black wire on coil) connects to +
Earth (earth point under coil is best, brown wires go to it) connect to the one with the earth symbol
Green wire terminal on coil connects to the square wave or "top hat" symbol,
Then the other two terminal will both now become +12V when engine runs (marked V, the two on the left of the diagram, back pair at right angle to the others). You only need to use (either) one to provide 12V feed to your fuel pump, and use the existing pump earth.
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MagicWagon
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Re: Electric fuel pump permanently running

Post by MagicWagon »

Awesome. Thanks everyone. I'll get one ordered !

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Re: Electric fuel pump permanently running

Post by MagicWagon »

Just an update. Ordered that relay and have fitted it. Works a treat. Thanks for such clear instructions. Even I couldn't manage to mess it up.
Cheers.
1983 2.0L Air Cooled Devon Moonraker

MagicWagon
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Re: Electric fuel pump permanently running

Post by MagicWagon »

Just realised, I ought to fit an in-line fuse to the fuel pump to as the PO has fitted it without one.
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