My son let his brother's 2006 g-35 roll backward in first gear trying to park on an incline, now sounds like its misfiring. we think the timing chain/belt is off. My fear is that we will have to pull the engine out to fix. Any input?

 

Will it go into gear and drive forward? Are there any diagnostic trouble codes? Usually a bigisfire will tell you which cylinder is causing the problem or a P0300 random misfire code.

Need more info, maybe a video too. Post the YouTube link here.