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The DeLorean has recycle fuel and it's flying in 1985 when Doc is sent to 1885.

So why doesn't the DeLorean have recycle fuel and couldn't fly in 1885?

still of the DeLorean in the mine

SQB
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user54273
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    Are you asking why they couldn't just put trash in the back of the DeLorean, like they did at the end of Back to the Future 1? – Jason Baker Oct 13 '15 at 01:21
  • Also, this is arguably a dupe of http://scifi.stackexchange.com/questions/95747/does-the-bttf-time-travel-require-fuel-power or http://scifi.stackexchange.com/questions/72570/how-is-the-delorean-powered-in-the-final-trip-back-in-time-in-back-to-the-future – Jason Baker Oct 13 '15 at 01:29
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    @Jason Baker - Neither of those questions are asking about why the DeLorean couldn't fly in 1885, so I don't think it's a duplicate of those. – Hypnosifl Oct 13 '15 at 02:05

2 Answers2

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The letter that Doc sent Marty after being struck by lightning and sent back to 1885, which Marty received in 1955 at the end of part II, said:

The lightning bolt that hit the DeLorean caused a gigawatt overload which scrambled the time circuits, activated the flux capacitor, and sent me back to 1885. The overload shorted out the time circuits and destroyed the flying circuits. Unfortunately, the car will never fly again.

So, the damage caused by the lightning explains why they can't fly. As for why they can't just put garbage into Mr. Fusion (which I think is what you mean by 'recycle fuel') so it can power the DeLorean to drive, it's explained that the engine which powers the wheels wasn't replaced during the hover-conversion, and it still runs on gas:

Doc: Alright then. Let's get the DeLorean and get ourselves back to the future!

Marty: Oh Doc, I tore a hole in the gas tank. We'll have to patch it up and get gas.

Doc: You mean we're out of gas?

Marty: Yeah, no big deal, we got Mr. Fusion, right?

Doc: Mr. Fusion powers the time circuits and the flux capacitor. But the internal combustion engine runs on ordinary gasoline; it always has. There's not going to be a gas station around here until some time in the next century. Without gasoline, we can't get the DeLorean up to 88 miles per hour.

Hypnosifl
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    I never liked the "no gas" explanation. Sure there were no gas stations but distilling oil should not be such a big deal for a freaking scientist that built a time machine. And there was plenty of OIL during that time. – Jakob Oct 13 '15 at 06:58
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    @Jakob - But Marty arrived on Sep. 2, and told Doc he was due to be shot only three days later on Sep. 5--only when Marty told him that did Doc begin to make plans to use the DeLorean, before that he had been content to live out the rest of his life as a blacksmith. Three days probably wasn't enough to figure out how to obtain enough oil and distill it into gas, even for Doc. – Hypnosifl Oct 13 '15 at 14:35
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Even though it's happened several times, the thing isn't really designed to be struck by lightning. Before Doc is sent back to 1885, we see the onboard computers are a little touchy to begin with. Frankly, he's lucky he survived the crash on arrival in the Old West.

Argyle
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