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Old 04-14-2013, 05:06 AM   #1 (permalink)
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Eliminating Diesel Fuel Shut Off Solenoid Power Usage

Hi,
I have and Arosa (Lupo) 1.7SDI which I am considering making alternatorless.
As part of this I'm obviously trying to reduce electrical power usage as much as possible before I start.
There is a shut off solenoid in the injection pump which is normally closed. When the ignition is powered on, it's coil is energised opening the solenoid. Once the ignition is switched off it springs back and cuts off the diesel flow killing the engine.
The problem is that it draws 2A just keeping itself open which adds a significant amount of electrical load - especially in summer when there are almost no other loads without lights etc running.

Options would seem to be to remove it's plunger and remove it's wire so that it's always open and perhaps install a normally open solenoid on the fuel line just before the injection pump.
Was just concerned that there might be issues with cutting off the fuel flow before the pump instead of at the existing shut off solenoid location?

I'd value any opinion on the matter.


Last edited by Fionn; 04-14-2013 at 04:23 PM.. Reason: typo
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Old 04-14-2013, 09:48 AM   #2 (permalink)
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You might cause excessive wear to the pump and I'm guessing it will be very hard to restart after running the pump dry. Ideally you'd convert the existing shutoff to only draw those 2 amps to shut the engine down. Or convert it to a mechanical shutoff. Less ideal would be to cut off the air going into the engine to shut it down. Just be sure whatever you use can't get sucked into the engine!
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Old 04-14-2013, 02:29 PM   #3 (permalink)
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Cheers GF, yes, I was worried about lack of lubrication in the early stages of the pump which was why I asked the question.
As you say reversing the solenoid would be the simplest solution, unfortunately the solenoid only has a single wire positive connection and uses it's outer threads as ground which makes this difficult.
I might buy a replacement solenoid and try to modify it internally to reverse it's action.
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Old 04-14-2013, 04:22 PM   #4 (permalink)
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Of course, you understand why diesels have normally closed fuel cutting solenoids?

Having that out of the why, if you can find a normally open replacement then that would be cool. Either way, making an engine kill switch is easy
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Old 04-14-2013, 04:32 PM   #5 (permalink)
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Yes, I fully understand why they are normally closed, to guarantee powering off in the event of a failure and so no power is consumed when the engine is off.
However solenoid type valves use a lot of energy to hold their non resting position (22-24W) in this case and a servo actuated cut off would be a much better option.
Of course reversing the current on the solenoid won't reverse the direction of travel anyway so my point above about the 1 wire etc is moot.
The difficulty with a servo based alternative is the mechanical interface into what is a pressurised (albeit relatively low pressure) area.
How is shut off achieved on more modern diesels, via the electronic injectors?
I'd really like to eliminate this load as it's pretty pointless and will add (2Ah x my desired runtime) to my battery requirement.
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Old 04-14-2013, 05:00 PM   #6 (permalink)
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If you can find a way to change the solenoid valve to normally open, make sure that you have a backup method to shut the engine off. And test that method before you change the valve.
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Old 04-14-2013, 05:03 PM   #7 (permalink)
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I will try it without the plunger to see if it shuts off anyway (IP has some measure of electronic controls), I suspect it might in which case I can just run it that way.
I could add a normally open solenoid valve to the input of the pump for emergency shut off or even a manual valve perhaps as it would be unlikely to ever be needed.
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Old 04-14-2013, 05:25 PM   #8 (permalink)
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I think first of all you should check if that cut off valve is used only for shutting down the engine. It can be used for DFCO as well and then you can't mess with it. It can be done easily with any light bulb, LED or voltmeter. If it's constantly under +12V you may try to find a solution to make it opened without drawing any current. I think that can be hard though, because it operates under fuel pressure.
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Old 04-14-2013, 05:28 PM   #9 (permalink)
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Thanks, I'll wire a bulb in parallel with it and see if it stays on solid before I try removing the plunger.
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Old 04-15-2013, 10:33 AM   #10 (permalink)
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What about a manual choke cable? No electrics at all, just a mechanical ball valve immediately upstream of the injector pump. No worries about what might happen if a wire breaks that way.

Of course if a cable breaks you're just as screwed but nothing's perfect.

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