I pulled over at a scenic overlook, and the car wouldn't fire back up. AAA were called, and arrived in 40 minutes. The car was trailered back to my apartment where I figured I'd give myself until Sunday to see if I could fix it myself. This happened on a Tuesday.
Let the investigations begin!
Quickly discovered my new shiny fuel pump was working OK, gas was getting to the fuel rail. Air filter was old, but removing it made no difference. Hooked a timing light up to #1 spark plug and bingo - no spark.
The previous owner had pointed out the electronic ignition kit he'd retro fitted, to make getting parts for it slightly easier. It replaces the 1970s transistor ignition circuit, which is hard to get hold of and unreliable.
I figured I'd replace the cheapest bit first, which was the HEI unit that he'd fitted. It looked like a cheap one, but they were heavily used by GM through the 90s so even the most expensive AC Delco ones are still $30.
You can see the heatsink that was fitted at the same time - 4 pieces of thin aluminium. The thermal paste on the HEI was also bone dry and probably not doing anything.
Temporarily fitted the new HEI on the old heatsink, and huzzah! Car fired right up.
So new thermal paste applied:
I figured whilst I was there, I'd upgrade the ignition coil as I didn't know anything about how old it was. It was still using the original ballast resistor by the looks of it. So replaced with a MSD Blaster 2, which was another $45:
I can't really tell if that made a difference, but I think a little of the stumble at high revolutions has gone.
I'm also fully aware this is a 40 year old car, and I should be grateful that I've only had one breakdown across the whole summer (which was ironically because of something that had been upgraded). To make diagnosing anything in the future a little easier, I also added an in-line 100PSI fuel pressure gauge.
Drove the car to work and back today, and everything seems right back to normal. Celebrated with a car wash.