Volvo 940 choking, then stalling in hot weather

So, my 94 Volvo 940 has about 315k miles on it and everything works great except during the intense heat of the summer. It drives fine for about an hour or two, but anything north of two hours with temps in the high 80s will cause the car to eventually stall - usually the engine just sounds like it’s misfiring for a few seconds, then I lay on the gas to find that there’s no acceleration and pull over where it will eventually shut down.

I let it cool down for about 15 minutes, then it will start fine and drive for a little while before stalling again. It seems that the longer I let it cool down, the more time I get out of it.

I’ve tried replacing the fuel relay and noise suppression relay. I always just guessed it was the noise suppression relay because it is located right next to the engine, and I just thought the soldering would melt when it gets too hot, then come back together after cooling. But, maybe this is totally off. I also replaced the mass air flow sensor before, but it had slightly different symptoms, and those have not come back. My problem now only happens on longer drives in the summer.

Any suggestions would be great!

Sounds like vapor lock or a bad fuel pump. With 315k miles, a bad fuel pump is likely. When it won’t start, see if you can hear the in-tank fuel pump running. If not, try the “fuel pump reanimation” method shown below. If banging on the tank gets the fuel pump going, you need a new pump.