Someone tried to steal this car recently, breaking off the top-hat end of the ignition lock cylinder and then jimmying the lock cylinder core with a screwdriver. I posted about that at Won't start after ignition lock cylinder replacement and relearn

My solution was to buy a used lock cylinder and key, remove the core, and install that in the original lock cylinder housing. Since the housing has the electronics, this allowed me to start the car without paying the dealer to run a relearning procedure with the electronics in the new lock cylinder.

Then I recoded the lock cylinder core tumblers so I could use my original keys for both starting the car and doors/trunk. Since I destroyed the original tumblers with drilling operations to remove the damaged lock cylinder, I only had the tumblers from the replacement lock cylinder to work with, and I didn't have the needed tumblers for 2 of the slots. I left those slots empty, which shouldn't matter as far as I know.

I thought the problem was happily behind me at that point. But the car has become hard to start. I thought it was only hard to start when warm, but now it seems that it may be hard to start all the time (though I'll need some more testing to confirm that).

The car cranks but does not fire. It seems like the battery has plenty of cranking power. There is often some clicking noises behind the dash, reminiscent of solenoid/relay clicking, or else of an intermittent electrical connection -- though I'm not smelling ozone.

The behavior is much like what I was experiencing before I realized that if you try to use a new lock cylinder housing with new electronics, then a programming scan tool must be used to start a relearning procedure. Until then, the car will crank, but the computer controls are sending a do-not-start signal and fuel injection is blocked. (See the other thread linked above.) However, the dash Theft light is not on, so presumably that's not the problem.

Any ideas on how to proceed?

Further troubleshooting starting with the basics: fuel and spark.

I did the easiest test first, and found that when the car won't start, there is no spark.

It does also seem that the problem is worse when the engine is warm.

I have not yet tried to work out what all could cause the no-spark, but wanted to post this much now.

just a guess - how about the crank position sensor?

Is the CEL on?

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There are a lot of things that can cause a no spark issue. Spark plugs,Coils, coil module, crank,cam sensors oil pressure sensor, pcm, ignition, and faulty wiring. Start a module get a test light and check for power going to coils if no check connected going to module and work your way back. But first check relays I've had many cause odd vehicle problems. O and if any codes would help is diagnose issues.