I have a 99 Caravan 3.8l that won't start. It will turn but doesn't start. I've changed plugs, wires, crank shaft positioning sensor, coil pack, and tcm still won't start. Now I'm told it's the pcm and not the tcm. I've been reading alot on here to see if the pcm serial numbers have to match exactly. I've seen that it does on newer models with anti-theft systems which my caravan does not have. So if I go to the scrap yard and pick up a used unit will it have a negative effect on my Caravan?

It could be the fuel system.
It could either flooding or starving for fuel.
If injectors are fouled badly it will wet the plugs and not fire.
If plugs are pitted that makes it easier to flood. (check plug tip condition, check all plug wires and boots are good)

If it is starving -- fuel pump weak (going to fail).
Need to test fuel pump pressure.

Check your PCM fuse

Cranks shaft doesnt have a direct effect on ignition. Cam Sensor does.

Crank sensor wont have any effect on starting, Cam position sensor would. Also check all your fuses.

sorry turns over means ZERO
the crank shaft can spin or not
the starter can in fact spin and crankshaft not.
and some think turns over means, engine runs. now that fact makes turns over, a dead statement.

the word is cranks over, the engine cranks over robustlyl
and then the engine runs.
then runs for more that 3 seconds, and the ASD relay holds. (step by step his works like this ,93 to now)

wont crank ? (clear statement in fact)
cranks ok, (crank shaft spins fast) can be seen and heard.
runs for 3 seconds? and stalls (ASD relay drop out) can be seen.
runs for 5min and stalls. (complex)
runs for hours and stalls. (even more complex)
all are key facts to the solution.

tell more..... tell all it does good bad or ugly
for better suggestions!

the crank sensor is on the back side of the engine just above the oil pan there will be two sensors there one is the crank sensor and the other is oil presser sensor. All so check the wires from the crank sensor to the cam sensor. If you think it is the timing belt pull the cover and check it. hope this helps.

try checking the crank shaft sensor, i had that problem with a 95 cirrus

Have you tried the reset method? Turn key to the ON position and leave it there for 10 minutes, or until the security light goes off. Then turn key to off, and back to on and start-see if it starts after letting it sit for a few minutes like that with the key in the on position.

Hi, if an engine cranks but refuses to start, it lacks ignition, fuel or compression. When the engine cranks normally but won't start, you need to check ignition, fuel and compression. Ignition is easy enough to check with a spark tester or by positioning a plug wire near a good ground. No spark? The most likely causes would be a failed ignition module, distributor pickup or crankshaft position (CKP) sensor.

you said you repl dist cap that means you don't have a crank sensor you have electronic ing module. remove your elec ing module have it tested most auto parts stores could test your module, or check your coil at the neg terminal. should have power. if not you lost your primary volt from your batt.your secondary power is coming from your electronic ing module from the module to the pos terminal on the coil, when the eng cranks,from the coil to the dist cap , from the dist cap center to the rotor then out to the plugs,this all happen pervided the timing belt or timing chain is ok. the cumbustion chainber needs 3 things , thats fuel, air, and spark.