Hi,

B.B. has a point about relays but didn’t come out and say why he didn’t trust junkyard pulls.
I suspect he thinks that they are used to some unknown degree. Well yeah that has some truths, unless that previous owner or his mechanic just put in a new one.

New ones are untested over a great amount of time so there is one dilemma right there. Or the quality of new as we have to remember, that lots of parts houses try not to provide very long warranties on electrical item for a reason. Coils of all types can be just like headlight bulbs.
What do you want to trust more?
Guess I’m a little facetious on this thought. (:-)

The point is B.B. is saying that is possible that the coil inside the relay is getting too warm and in six minutes it fails to continue to magnetize.
I had a system relay fail that way or it can be a bad terminal connection onto that relay.
Especially if it goes to a large current user like a fuel pump.
Same thing goes for the trace soldering of circuit boards as we know on the 240s.

This intermittent needs some cross diagnostics and that is why I suggested the starting fluid to help point out fuel over drop of ignition sparks.
One or the other is turning off and a signal light from the ignition would be helpful.
A timing light on the secondary side of the coil or a test light on the negative side of the ignition coil might help.
That side of the coil gets turned on and then off to fire the plugs. The bulb goes out it fires. During cranking it is slow and should blink.

So it dies when it get hot, is a clue that fits above, but what about the other times, if its not?

Ya gotta find out what’s not happening and back up through the system that provides that missing component of combustion.

Hope this helps you think this out.

Phil