1997 Ram won't start when hot.
 

I have a 97 ram, 5.9. I have an issue with starting. Starts fine when cold. Will not start until it cools off. I replaced the coil and coil wire. Still wouldn't start, just cranks. Had to have it towed home yesterday, about 15 miles. Got it off the wrecker and it started right up. Went out this morning, started right up. Let it warm up 20/30 minutes. Pulled it into the garage, won't start. I let it cool off about an hour, started right up.

Does it quit while driving? Or just won't restart?

Replaced the crankshaft position sensor, spark plugs, plug wires, dist. cap, and rotor. Just will not restart when warmed up

Find out what's missing when it won't start. Spark, or fuel.

I can hear the fuel pump prime up. I've tried to put a spark plug in the coil wire while grounding to the engine block. NO spark until cools off ( approx. 45 minutes). The only OBD codes on the list are PO 135 sensor heater circuit malfunction (bank one sensor one) and PO 456 Evap leak. Would an O2 sensor cause the non start

Nope. PCM ignores O2 sensors during start up. No spark means either bad coil, bad crank position sensor, or bad PCM. More often than not, its the crank sensor.

replaced crank sensor and the coil with the tune up hoping that was it. IF it's the PCM, is it just a "plug and play" ?

looking at PCM's from O'reilly's, they have both kinds, Preset from the factory and units that say " this is a flash unit". What does that mean and which do I get

you would wanna get the preset from the factory and make sure its for the same year. but before i did that i would look into the spark issue more. get the engine hot and check for spark. no spark? ok lets check the connector at the coil and see what its reading, if its not getting a single to the coil then we know where to run to from there. i had a bad coil once and it would run but when it got hot it would just shut off, but your issue is it just wont restart, so it sound like its in the connection not the coil itself.

Yep, being its a 97, I think getting the Preset PCM would indeed be plug and play. (prug and pray?) I suspect the 'flash unit' is blank, and you need to load a tune on it. I don't *think* the 97 would have to be flashed to your VIN, but, I am not 100% sure on that.

Could try an experiment..... grab a blow dryer, or, if you are careful..... a heat gun. Start the engine, point weapon of choice at PCM, get it warm, see if the engine quits.

Sounds like a heat soak problem....... something is getting hot, expanding, and breaking a circuit...... As ryan suggests, fairly easy to test, when the truck won't start, just put a test light across the terminals for the coil electrical connector. See if its flashing. If it is, probably bad coil. (yeah, I know..... its "new"..... don't mean squat. :) ) If it doesn't, that more than likely means the coil is fine. Given the crank sensor is also new..... I am leaning pretty hard toward the PCM. But, before spending the money, what brand crank sensor did you get?