Replaced bad coil van cranks but wont start?

You must mean coil pack? It's very unlikely that the whole pack of coils suddenly go bad. The proper test procedure is to first determine if the coil pack is getting a primary signal (battery voltage) with the key in on, not start. Then one can opt to test each individual coil with an ohmmeter. This usually spots a bad coil. But again if it just suddenly wont start and run, the odds of a bad coil are low.
What usually happens is the Ignition Control Module (ICM) may be the problem or the crank position sensor could be the problem. Find videos on YouTube how to test the ignition system-there are almost surely videos for mercury vans.

The ECU module controls the spark. If you have a bad crank sensor. no spark even with a good ECU.

I would suggest changing the pickup in the bottom of the distributor. Also crank the engine with the cap off of the distributor and make sure that the rotor bug is turning and make sure there is 12v at the coil with the key on.

Are the plugs firing if not check the coil need to know exactly what's happening

The parts you replaced don't typically fail due to heat/cold cycles.You need to see if it might be the ignition coil.Make the coil easily accessable(take of the engine cover).Have a 12v test light and some sort of spark tester handy.Start the engine,let it run until it quits.See if you have spark at the coil.If not, unplug the low voltage connector on the coil,and put the test light across the connector,and crank the engine.The light should flash on and off.If it does,replace the ignition coil. If it doesn't flash,you may have a bad crank sensor,but this usually won't make it shut off,instead,it will cause it not to restart after heat soaking for a couple minutes.(I'm betting on the igniton coil).

A test light connected across the coil primary leads should flash on + off when engine cranks(coil sparks when 12v turned OFF due to collapse of magnetic field).If you get pulsed 12 volts,and no spark from the coil,the coil is bad.If you don't get the pulsed 12 volts,trace back to find out why(the PCM turns the coil ground on and off,12 volts comes from switched IGN source)

I'm not familiar with dodge but I know Ford's and GM's have ignition modules that go out and you lose spark.

Well you hit all the major ones, could be crank position sensor, ignition module, a bad coil pack (it should have 3), you need to check that you have spark to each plug while the engine is turning over (!!!be careful as this will hurt if you get shocked!!!), this will rule out coil packs. if you have no spark to any plug your looking at a bad ingnition module (which is what the coil packs bolt to). Hope this gets you on the right track!

we get remans bad out of the box......... good luck

I know this may sound simple and dumb, but have you checked your ground wire?