3.8 motor cranks but won't start?

An engine needs three things to start: 1. fuel; the engine must have the proper amount of fuel delivered to the cylinders. 2. ignition; the engine must have an adequately strong spark at the spark plugs, delivered at the right time. 3. compression; an air/fuel mixture must be drawn into the cylinders then compressed as the piston rises to the top of the compression cycle. If all three conditions are met as the engine is turned (either by the starter or by "push start") the engine MUST run. To discover why the engine won't start, you need to find out which of the above is not taking place or not taking place properly. Insufficient or too much fuel can certainly cause an engine to not start. A non-existant weak or improperly timed ignition spark can certainly cause an engine to not start. Low on non-existant compression cancertainly cause an engine to not start. If you suspect that there is no or insufficient fuel, I always recommend that people try a little starting fluid. One common problem this time of year is "condensate" in the fuel line. If a few drops of water condensate builds up in a line, then the line freezes, no fuel will get past and your engine won't start. It's always a good idea to use a can of fuel line de-icer once or twice through the winter. Typically, if there is a problem with the ignition system, modern automobile computers will report a "fault" by flashing the "check engine" light. If that's going on, use a code scanner to find out what's wrong. All you can do is start to narrow down the problem, isolating different "sub-systems" to see what's keeping the engine from running.