Cranks but will not start

Idle speed is going to be too low until you do the "minimum throttle" relearn procedure. Until then, you might need to hold the accelerator pedal down 1/4" to get the engine to run, and to not stall at stop signs. You also will not have diagnostic fault codes if the battery or engine computer were disconnected.

First, check for steady spark during cranking. If that is missing, check if the automatic shutdown, (ASD) relay is turning on during cranking. The easiest way to do that is to check for twelve volts on the wire that is the same color at every injector and ignition coil. Most commonly that is a dark green/orange wire.

Do not be confused by the terminology. The engine computer turns the ASD relay on for one second when you turn on the ignition switch. That relay sends voltage to the ignition coil(s), injectors, alternator field, oxygen sensor heaters, and fuel pump or pump relay. If you hear the hum of the fuel pump for one second when you turn the ignition switch on, the ASD relay is working, and the computer has control of it.

During cranking, the crankshaft position sensor and camshaft position sensor send signals to the computer. That is how the computer knows the engine is rotating, and in response, turns the ASD relay on again. The purpose is if a fuel line is ruptured in a crash, the engine cannot run without fuel pressure. The engine stalls, then the signals stop arriving from the two sensors. The computer turns the relay off, and that stops the fuel pump from dumping raw fuel onto the ground. This system is very effective and trouble-free. Almost all problems are caused by those two sensors.

Where most people get lost in this circuit is they find no spark or no injector pulses, and they stop there and try to diagnose those systems. About ninety five percent of crank/no-starts are caused by one of those sensors, resulting in loss of injector pulses and spark. You have to check for both so you do not waste time in the wrong system.

To add to the misery, it is common to not set a fault code for a missing sensor signal when simply cranking the engine. Typically those codes only have time to set while a stalled engine is coasting to a stop. I have a Chrysler DRB3 scanner for all of my vehicles. On the live data screens, it shows those sensors with a "no" or "present" to tell if the sensors' signals are being received during cranking. You are determining the same thing when you check for twelve volts at an injector or ignition coil.