Come on guys... No ideas? It doesn't want to start after it gets good and heat soaked. Someone must have been through this before with a 502?

as already said earlier,HALL EFFECT SWITCH INSIDE THE DIST,seen it go bad many times.

make sure you have full power going to the module for the ignotion,,what happens when you fire the engine the starter solenoid feeds power back to the ignition and it will fire when the key is in the start position. try this,,keep the key in the crank position a little longer after the engine fires,if it stays running with the key in the crank position then you lost power to your ignition (check the wires at the back of the key switch) or the module pass's power through the backside circuit in the ignition module and will let it fire when in the crank position..it will start cold then will die or wont start back up when its hot and needs to cool down thwn will start after a whyle..Change the ignition module after you make sure you have power at the wire harness.

MPI or carb????? It sounds like it could be vapor lock also.

I really don't understand how you have the ability to rebuild an engine and then not be able troubleshoot this problem.

I noticed your Baja is a 97, does it have a VST tank? It would be a tank on the rear port side between the intake and ECU, which the manual fuel pump fills with fuel, then the high pressure pump sedns fuel to the injectors. If it has one, then the next time you have a problem unscrew the plug off the top of it to relieve any vapor lock pressure. It just takes a crescent wrench. If it starts right up then, you have problems with the VST tank and vapor lock, but will get you going again. I wouldn't drive with the plug off, but at least you would know where your problem is at. There is a diaphram in it that is supposed to open with vacuum when the motor starts to relieve the pressure. Even if everything is working right it may still vapor lock, and I'm guessing one reason why they quit using that setup.

read ^^^ needs a ignition module...

Get the merc shop manual, #16 i think, and start down thru the flow chart and u will find the problem. Otherwise u are just guessing and wasting time and money trying this or that.

Its online.

The VST tank also has a screen in it. An old mechanic told me that the fuel apparently backflows after you kill it and can stop up around that screen if it's dirty. I think it is a 300 hour part and kind of pricey.

The ICM does funny stuff too. I'd replace it. My cap, rotor and ICM all look tired after 100 hours.

If a hammer or pliers won't fix it, you have an electrical problem. Right?

10-4 boss. A hammer should fix this one.