Greg, you might want to go back and re-read the OPs post, the hard/no start occurs under two conditions;
1) Low fuel level 2) Ambient above 70 degreesNeither one of these conditions is worth attributing to vapor lock. Hell, I just drove over 100 miles on Sunday in 100 degree heat in a carbureted car with an engine mounted mechanical fuel pump, the coolant was running at over 230 degrees, the gasoline is reformulated piss water and I experienced absolutely no evidence of vapor lock.
Sorry, at 72 degrees, he doesn't have vapor lock.
He has the classic pattern failure of a weak fuel pump.
Which means that the vapor lock is a symptom, not the cause of the problem to begin with, i.e., he has a failing fuel pump.
All well and good, except that it doesn't fit the OPs description of when the problem occurs. Wrong diagnosis.
I guess if you follow the TSB, you -might- stumble upon the root cause for the no start. Thing is; I have numerous customers who own 2.7 LH cars and they do not suffer wholesale vapor lock problems with their cars under
-any- ambient temperature conditions.
The OPs problem occurs at ambient temperature above 70 degrees with low fuel level. No mention of a "hot engine," so the TSB doesn't fit. A simple amp meter hook up to the fuel pump circuit will show lower than normal amperage draw for the fuel pump which means it's spinning faster than normal, it's spinning faster than normal because it's cavitating, it's cavitating because the pump is worn out and lacks sufficient volume to maintain an adequate level of fuel in the cup at the bottom of the fuel pump module (via the return line) so the pump is starving. If you guys had the slightest clue of how this system -actually- works, and had actually paid attention to the customers complaint, non of this back and forth crap would be necessary.
Sounds like a fuel pump failure, not vapor lock. Vapor lock occurs in spite of a properly functioning fuel supply. Frankly, I haven't seen a case of vapor lock in near 25 years, but then, I DO know to recognize the symptoms when they are presented (like the OPs mention of missfiring when the problem occurs).