It would be more likely a cam sensor improperly aligned could cause a condition your speaking of since its job is to tell the PCM when the engine is on TDC #1 post on. The crank sensor will provide position for each cylinder vis the flex plate or flywheel position to provide the sequential fuel injection firing and the ignition timing firing order as well. Although you feel that spark is occurring early and both sensors alignment are essential it is still equally important to know that the valve timing is correct . Realizing that your trying to avoid excess disassembly but it may become necessary to confirm timing gears and chain still in alignment. The other thing on my mind is to confirm if the is no issue with the harmonic balancer that it still displays the correct position . If the rubber dampening material has slipped and allowed the outer ring to spin out its true position and fool us to believe that the zero TDC mark is still true of it isn't and the crankshaft is off some degrees that will create havoc with valve timing , cam and crank sensor alignment too. I know it wouldn't seem likely for a low milage engine to have trouble with its timing chain or harmonic balancer but we still haven't found the cause of the no start and the back firing and I feel that these are items that must be confirmed if in good working order and correct alignment. Before we can suspect a sensor , we should be sure that the engine is sound mechanically . It is also the reason I suggested the compression test . I say we take our cue from that test which will show all is well or not . Yes , back fire is likely caused by ignition timing but since there is no distributor it falls on valve timing and cam and crank sensor timing so yes , I follow your questioning. I do agree that cut to chase may bring luck but it's just my personal way to be certain by eliminating posibilities by checking components . I'm sure you know that if a chain , cam and crank sprocket are in correct valve time and a harmonic balancer is pointing to TDC then a cam sensor can be installed correct as well as a crank sensor reading the flex plate in correct position should get an engine started provided all components such as ignition coils for example are good as well. It still has me thinking about your observation of the #3 & 4 exhaust valves not fulling opening. The compression test will reveal more . Don't want to give scenarios like collapsed lifters , worn cam lobes as those are extreme and still not proven in this case. Just giving direction to test for . No,start and back fire , that is the focus. It ran shortly , back fired and stalled . Almost sounds like bad coil(s) but I still like to be thorough and check mechanically as I did once on a Buick 3800 V6 of all the items I posted here. We swapped the coils and module on to,another car and it ran but not on the car with the problem. Yes , these things throw us but is still like to be through . It's helpful. Sorry I'm such a stickler.
