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DO NOT FEED THE TROLLS!
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So, there's that TV series "Revolution" where, for whatever reason, electricity doesn't work properly with machines anymore. I haven't watched the show particularly, but from what I gather, the only vehicles that work are ones where the occupants have some kind of MacGuffin that lets the electricity work in a small area.

I've been considering a Cummins swap into my '82 Dodge, and most people recommend the 12V for the ease of conversion. I looked a bit into the differences between the 12V and 24V, and the first things I found were all related to the fuel injection system, specifically the introduction of electronic stuff. That got me thinking about this TV show...

Would a 12V Cummins engine run, once started, without any electrical system whatsoever? If so, if such an engine were mated to either a manual transmission or to a fully-hydraulic automatic, the truck should theoretically move under its own power, even if things like lights and electric-draw power accessories don't function. Obviously starting such a truck would be a challenge and would probably require some kind of mechanical interface out the front or from a PTO to let a different machine initially spin the engine to start it.

It just got me thinking that between the diesel engine and the steam engine, the universe of that TV show left out rather important sources of mechanical power that would have let society fall no further than a nineteen-teens tech level as far as the ability to operate factories and otherwise continue production on some kinds of things. There wouldn't be a need to resort to the bow and arrow when more sophisticated weapons could be produced mechanically. Even many of our more sophisticated inventions like air conditioning are still mechanical in nature, and could be adapted to run in some fashion without electric current flowing through wires...
 

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It will run without the electricity, given no electronic sensors these days to make the thing operate, but in olden days, once the glow plug has had time to have the heat source working, no electricty is needed to stay running. The one and only problem is, a heat source to have that initial explosion start the engine rotating. If that can be done in a neanderathal means of a torch to heat up the glow plug and the vehicle then push started, or going down hill to get it to turn over, it may actually work. Now, if you had a dynamo you could hand crank in order to get the glow plugs to heat up that way, hand cranking is going to be real difficult with a diesel what with the compression, so a starter would be nice, or making sure you can park on a really steep hill every time would be nice.
 

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Fuel injectors were mostly mechanical (cam-driven) once, but are now almost all electronic. So it would require a step back, and, as dana says, no sensors and no electrical accessories of any kind. If you've ever had vacuum-operated windshield wipers, as we did on our fire trucks, you would not want to do this.
 

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A few interesting facts,

Cummins uses a "grid heater" in the intake to warm the air on cold days, not glow plugs.

No throttle plate, thus no manifold vacuum. The engine speed is controlled by a valve in the injector pump that moves more or less fuel. Brake vacuum is supplied by an external pump.

Yes, a diesel engine requires no electricity to run.

As far as the swap, the advantage of 24v is the ability to use smaller gauge wire to conduct equal wattage. Not a game changer in your SHTF scenario, however living at the top of the hill...
 
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