Start with the basics, and work your way up, Last tune up was? Wires plugs ALL filters? If all that is ok, check for a stuck EGR, then test fuel pump pressure, If it won't restart, determine what's missing, the engine needs three things to run, Spark at all plugs, gas to all cylinders, and compression in all cylinders, tho an engine may run lacking one in one cylinder, it won't run very well!
http://www.2carpros.com/car_repair_video/test_fuel_injection_pressure.htm
Go here and checkout our video.
http://www.2carpros.com/car_repair_video/test_engine_ignition_system.htm
and this one!
http://www.2carpros.com/first_things/car_cranks_but_wont_start.htm
http://www.2carpros.com/dia/how_to_check_compression.htm
http://www.2carpros.com/dia/index.htm
If you smell gas, check your oil level too, gas can be washing the cylider walls and filling up the crankcase...not good, this can and will damage the engine!

Answered by merlin2021 (expert)
18,145 answers provided