Hey guys I'm hoping someone can help me out here. I've got a 2006 hyundai elantra that died on me while downshifting into first from third at a stop sign. Slowed down, downshifted and as soon as I gave it gas to speed back up it sputtered and died. Doesn't seem to be electrical since it turns, it just won't start. The only code that was on it both before and after this happened was like p0420 or whatever, meant my cat was running lean, maybe bc of a **** o2 sensor which I swapped. I've charged the battery, tried jumping it, replaced the alternator, spark plugs, crankshaft, checked the starter, and tried starting it with starter fluid. There's spark going to the plugs though if they are sparking idk for sure. It just turns and turns and just doesn't start. If anyone has any idea what could've happened or even just another troubleshooting method to get some more information, that'd be great. Absolutely nothing I or my mechanic friends have tried have gotten the situation to move at all, as long as this isn't irreparable seeing I'm not exactly in a position to buy another car.