Question about Energon in the films

So we're told that the Allspark is what powers Cybertron, that it is an Energon source, and that it is needed to rebuild the Transformers home.
Apparently the Allspark contains a tremendous, yet finite amount of Energon. When it is depleted, it must be re-filled using a solar harvester.
If the Fallen was on Earth 17,000 years ago to build a solar harvester, that must mean that the Allspark was getting close to empty. The harvester is never activated, thanks to the intervention of the Primes. Thousands of years pass, war rages between the Autobots and Decepticons, and presumably more Energon is drained from the Allspark. Megatron wants all the Energon for himself, so Optimus launches the Allspark into space so that Megatron can't get his hands on it. In a huge coincidence, the Allspark just happens to land on the exact same planet on which the harvester was constructed.
So now the Transformers have no Energon supply whatsoever. Despite this, they follow the Allspark and continue their fight on Earth, as we saw in the two films. Despite the Allspark's Energon levels being low, it still is capable of repairing Frenzy's body, fueling certain devices at the Sector 7 base, incapacitating Megatron with its "raw power," and later reviving the Decepticon leader using a mere shard.
So if during the events of the two movies, the Transformers don't have an Energon supply, how are they able to function? Jetfire is rusting and falling apart from Energon starvation, yet the other Transformers seem perfectly fine. I mean...maybe just before the Cube was launched into space, they all had Energon reserves stockpiled and were surviving on that. But after the destruction of the Allspark, the Autobots don't seem concerned in the slightest. What exactly were they planning on doing for Energon? Are they running on diesel now? If they can run on fossil fuels, then why do they need Energon?
Apparently the Allspark contains a tremendous, yet finite amount of Energon. When it is depleted, it must be re-filled using a solar harvester.
If the Fallen was on Earth 17,000 years ago to build a solar harvester, that must mean that the Allspark was getting close to empty. The harvester is never activated, thanks to the intervention of the Primes. Thousands of years pass, war rages between the Autobots and Decepticons, and presumably more Energon is drained from the Allspark. Megatron wants all the Energon for himself, so Optimus launches the Allspark into space so that Megatron can't get his hands on it. In a huge coincidence, the Allspark just happens to land on the exact same planet on which the harvester was constructed.
So now the Transformers have no Energon supply whatsoever. Despite this, they follow the Allspark and continue their fight on Earth, as we saw in the two films. Despite the Allspark's Energon levels being low, it still is capable of repairing Frenzy's body, fueling certain devices at the Sector 7 base, incapacitating Megatron with its "raw power," and later reviving the Decepticon leader using a mere shard.
So if during the events of the two movies, the Transformers don't have an Energon supply, how are they able to function? Jetfire is rusting and falling apart from Energon starvation, yet the other Transformers seem perfectly fine. I mean...maybe just before the Cube was launched into space, they all had Energon reserves stockpiled and were surviving on that. But after the destruction of the Allspark, the Autobots don't seem concerned in the slightest. What exactly were they planning on doing for Energon? Are they running on diesel now? If they can run on fossil fuels, then why do they need Energon?