Alright, I'm at my wit's end with this. Slowly getting ready to add boost, but this has been one of the last issues I'm chasing. I've tried asking on another forum....but figured it'd be a better idea to ask on here. Car runs great otherwise, aside from an occasional idle dip.

2002 NB ~45k miles. Stock aside from a few preventative maintenance items.
Coolant Reroute
Standalone Fuel Pump Relay (direct to battery)
Within the last 10k miles: spark plugs, timing belt, marathon battery

It will start when it is cold without issue, but will only crank with no start when it is fully warmed up. A push start will get it started...somehow throwing a jump pack on it will make the trunk lights brighter, it will crank faster and it will start up.

I've just been doing round trips to avoid the issue for a while. It's driven 3-4 times a week, but otherwise the battery is always put on a trickle charger.)

Alternator is reading 14v at idle. I've tried swapping a main relay and/or cam position sensor while hot and still no luck. Recently I wired my fuel pump to it's own separate relay just in case I was actually killing main relays, but still the same issue.

Not sure what else I should try diagnosing. I saw somewhere someone made a comment that the Marathon/Westco/EastPenn battery could be a culprit. Anyone else have a similiar issue?

 

This may sound like long shot, but have you checked the battery terminals for corrosion/tightness?
I know a battery post problem manifests itself mostly in cold conditions, but it's worth a look.

Same goes for the B+ connections on the starter and the M6 bolt in the underhood fuse box.
I would check the grounds at the back of the PPF, and the grounding strap next to the oil dipstick, too.

Also, I have seen starters act up when hot. They take a ton of amps and crank slowly when that happens.
If you have a voltmeter, please record the voltage while cranking - cold and hot.


Since I have no way of getting my hands - and my eyes and ears - on the car, I have resort to guessing based on the info in your post.

 

Double checked the battery terminals a few days ago when I brought the battery over to get tested (took it out of the car and then put it back in). I'll go through those grounds and check the voltage today. The starter does not noticeably crank any differently between cold or hot...just much faster when I have the jump pack on it.

 

Could you please define "hot" and "cold"?
I mean, is cold anything below, say 50F, or, is it whatever your heated garage temp stays at?

Come to think of it, have you checked your CTS?
A bad CTS, as well as frayed / corroded / open wiring of the sensor will report very cold temps to the ECU and it will command a very rich starting injector pulse width.
This may be OK in cold conditions where more fuel is needed to start, but it will inevitably flood the engine when it is hot.
A quick way to test this scenario - albeit not definitive - would be to floor the gas pedal while cranking in hot conditions.
Full throttle while cranking is "clear flood" mode, so the injectors do not spray while cranking.
Worth a try.

 

The issue has been happening regardless of ambient temperature. Hot being anything 60 to 100. Cold being 30-60. It will basically start at any temperature without a problem. Hot start issue is always consistent. For an NB...checked the coolant temperature sensor with multimeter, obd2 reading and making sure the AC turns on both fans. Is that a correct diagnosis?

Haven't had the chance to go under the car just yet to check the ppf ground yet.

 

CTS and fan switch are two different things.
(sorry, I'm in a rush)

 

Update. Got the coolant temperature sensor in...still no change unfortunately. Still cranking and no start only when hot. Time to work through the grounds and check the voltage of the starter.