My own guess is the GP's are OK but do check them first. I say this because at 100F ambient that car should start without GPs working though you might have to crank it for 5-10 seconds or so to get it to start. If it were GPs it still should start.

When was the last time you adjusted the valves? You might have a combination of poor compression due to tight valve clearance and bad GPs that is causing the problem (it might have been masked by the GPs but now you are seeing both issues crop up).

So, in short you might have a GP problem but if it were the only problem you should still be able to start the car with a bit of cranking...if it would not start then I would say you might have more than one problem.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz