i have a 2004 montecarlo 3.4 i just bought, it was not running so ichecked it and the fuel pressure regulator and the injector #2 were bad so i replaced them but the engine cranks but dont start it has about 50 psi of fuel, good injector pulse, good spark, good compression, no codes im thinking it coul be the timming chain jumped because is like it wants to start but you can hear little explosions some times and the firing order is good too, how can i check for timming marks without removing the timming cover??,