Dear mid-60s Buick caregivers who are constantly learning more about their vehicles,
Alas, my trusty wagon is still being dogged by some sort of electrical problem. I went back to my first hunch that the electronic fuel injection system was somehow to blame and so decided to log an extended drive to catch the system goofing off. I spotted a problem as soon as I started the engine:
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You can click on the image for a nice big graph. I poured over the remainder of the drive and the EFI system is working as it should. So I'm back to the hypothesis that the alternator has some sort of intermittent voltage regulation problem.
I was able to confirm something else that I has suspected for a long time. I also have a personal weather station and make graphs of the conditions. Here is the outside air temperature during the time of my drive:
It was an unusually cool day with the air temperatures not exceeding 74? F the entire drive.
However, Biquette's throttle body has a sensor measuring the temperature entering from the air filter. That shows something
very different!
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As with the previous EFI graph, you can click on it to get a larger image. What you can see is as the drive continued the temperature at the throttle body climbed well above the ambient air temperature. This isn't a big surprise. Biquette has one of those open style air filter holders:

These are very popular, but they force the engine to pull air that has been already pulled past the radiator and over the heads. As a result, the air entering the engine was over 30? warmer than the ambient air. That's fine on a cool day like this, but imagine touring Route-66 with the air temperatures closer 100? F. Asking your engine to ingest air at 130? is definitely increasing the risk of premature detonation. Since I'm still hoping to haul a heavy vintage travel trailer with Biquette, I think I have no choice but to come up with some sort of cold air intake one of these days.
Alas, I don't have any easy way to replicate this run using a stock-style snorkel air cleaner. However, I would bet the air temperatures are significantly less than with these open-style air filter holders. So that is a pragmatic reason to stick with the factory air cleaner assembly.
Cheers, Edouard