Ran When Parked

Michelle pokes her head out from underneath the train.
I think that's it.
She puts a large piece of leftover hose aside and crawls out.
That was quick – nice job.
Jack walks over to the compartment holding the batteries, takes the cables off the terminals, and hooks them up to the generator he had turned into a makeshift power supply. He starts it and climbs into the train. Michelle follows him and they go to the driver's cabin. Jack turns a key switch and part of the dashboard lights up. Then, he pushes the engine start button. The engine begins to turn over. While holding the button, Jack points to the fuel pressure gauge, slightly raising his voice to talk over the engine:
That's progress already.
The needle on the gauge slowly creeps to the right.
Too slow though, he adds after a moment.
He holds the button for a while, the engine keeps turning over, but it doesn't seem to fire even once.

Michelle suggests they take a look at the fuel injection. Jack turns the key switch off again and they go to the middle of the railcar. The floor panels above the engine bay are already missing, they had removed them earlier to replace the bits of rotting hose in the fuel line. Jack grabs the manual from one of the seats and starts flipping through the pages while Michelle jumps out and stops the generator. He begins to undo knowledge gap here: How does that work? What do you undo to fix a gunked-up fuel injection? Also, do/did diesel engines have a carb?

After cleaning out gunk and doing some makeshift fix, they try again. The engine attempts to start a few times but it still doesn't run. Michelle notices the fuel pressure is back down to zero so they pull the line out to see what's going on. Michelle waits next to the train, holding the end of the fuel line over a bucket while Jack returns to the driver's cabin. suggestions for improvements welcome

He presses the button for a few seconds, then he leans out of the window looking at Michelle and the bucket. She looks up at him and says:
Barely a few drips. But there's pressure on the other side of the fuel filter.
So we need a new one?

He walks over to the closest door and jumps out. Michelle begins undoing the clamps holding the fuel line to the filter while Jack starts searching all drawers and boxes in the vicinity for a replacement. One side of the filter comes loose and Michelle starts with the other side.

Not the right one but I found this.
Jack holds up a box he found in a drawer. He opens it while walking back to Michelle and pulls out a fuel filter that is significantly larger than the one pulled from the train. The fuel line fits inside it so they add a piece of larger hose over that and put multiple hose clamps around both.

Michelle climbs back inside, Jack starts the generator again and follows her.
Ready? She has her fingers on the engine start button.
Go for it.
It takes a while but the engine eventually sputters to life. Michelle lets go of the button and it keeps running.

A few hours pass as they fix up a bunch of other small things around the train and put the floor panels back in. While climbing around the storage shelves in the hall/hangar?, he finds a crate of dried-out lead-acid batteries. After adding some water and letting them sit for a while to dissolve the acid, he shoves them into the battery compartment and connects the cables.
Michelle, can you turn the switch?
Nothing.
I figured. Let's see if...
He connects the generator back to the train and starts it.
Start the engine, I'm wanna see if we can charge the batteries like this.
With the engine running, he wraps some loose wires around the battery terminals and connects them to the generator, causing quite a few sparks to fly. The generator's engine sounds like it's suddenly struggling under heavy load. He yanks the wires out but a few bits of them have already fused with the battery terminals. Okay, that was truly a room temperature IQ move.
He disconnects the train from the generator and waits for a moment to see if its engine will continue running without electricity. It does, so he forces the lugs onto the battery terminals which now have pieces of wire stuck to them.
Michelle leans out of the window and says: The gauge with the battery symbol just jumped to the red line.
If it's not past it, should be fine.
Well, slightly?
Jack climbs into the train and goes to the driver's cabin.
Nah this is fiiiine.

After giving the dashboard a once-over and leaning out of the window to check that the train is free to move, he attempts to disengage the brakes. Nothing happens. He flips a few switches and a compressor starts puttering away under the floor. The next attempt to disengage the brakes is met with a lot of hissing from underneath the train, but nothing else happens.