Japanese Army runs out of Oil by the summer of 1942 at the very latest.
Kwantung Army gets utterly destroyed by the Red Army Far Eastern Front (which, as is noted here regularly, was NEVER weakened at any point in the war) with it's 3,000 light tanks and 430,000 combat troops fighting from prepared defensive positions.
Lacking oil the Japanese forces in China lose both the advantage in mobility and air supremacy while the Nationalist Chinese retain access to Western, primarily American, aid coming over the Burma Road. With massive logistical difficulties the IJA is unable to hold many of its advanced position and has to fall back with nothing better than air parity as the IJN also runs through its oil reserves (or has them transferred to the Army by the Imperial General Staff) and is largely imobilized reducing the IJN's capacity to provide support for the Japanese Army. Sometime in the second half of 1942 the Chinese clear a section of the coast, likely somewhere northeast of Hong Kong or the mainland region near Hong Hong itself, and the flow of U.S. aid into China goes from a trickle to a torrent as the deliver method goes from truck over a relative goat path to cargo ship unload 10,000 tons of materiel at a time.
Sometime in 1943 the Japanese do something idiotic (like attack a U.S. flagged Liberty ship sailing into Hong Kong) and find themselves in a War with the United States. This is, of course the post 1940 Two-Oceans Navy Act version of the U.S. military with at least 10 fleet carriers, Hellcats and Avengers, with 8 fast battleships and 30 or so new cruisers and 100+ new destroyers. Japanese bases on Formosa fall under air attack by B-24G bombers with P-38 escorts (the Lightening have been found to be less useful as a bomber escort than its single engine P-47 and early P-51 rivals) with IJN air assets, especially fighters having been victimized by lack of fuel for training, being qualatively as well as quantitatively inferior to the newer, much more rugged U.S. designs.
Much the same fate befalls Saipan as the recently completed and fully updated U.S. facilities on Guam are used to stage crippling air attacks against the Japanese Mandates. Again , lack of fuel, not just for aircraft, but for the logistical needs of the IJA/IJN forces on the Island means the U.S. rapidly gains complete air supremacy over the Island.
By mid-1944 the Japanese have been pushed out of China, are fighting to maintain what is left of their position in Manchukuo and the Korean Peninsula against a combined Chinese/U.S. ground force coming from the West while a Red Army advance comes from the East.. Japan is under nearly daily heavy air bombardment from American bases in China, on the recently captured Formosa, and likely Okinawa, where the 15,000 poorly equipped defenders were obliterated in three weeks of hard fighting,
The U.S. establishes a air-tight naval, submarine, and air blockade of Japan while Russian aircraft pummel Hokkaido, occupy the Kuriles, and Sakhalin before the end of 1944.
tl;dr: The Japanese get fed their lungs.
