[Porsche-O-Phile]

I'm going to take a guess and guess excessive hydrostatic pressure on the wall causing a localized stress failure. If there's rebar in the CMU foundation (as there SHOULD be, but given how lousy residential construction practices are sometimes, I make this assumption carefully. . .) then the rebar should help hold things together on the tension side of the wall. Concrete is notoriously weak in tension but very strong in compression, which is why steel is typically added to concrete to increase its ability to resist failure in bending under load. Anyway, my point is that you probably don't have to worry about a structural failure with a crack like that, but you could have issues with moisture infiltration depending on (again) what kind of construction practices were used. If there's a moisture barrier on the outside of the CMU (as there should be), you should be fine. If there's not, or if it has failed/ruptured/torn you'll see evidence of staining and moisture infiltration around the crack. I don't see that in the photo so you're probably okay.

I'd say grouting is only going to fail again in the same way. You're probably better using some sort of epoxy or elastomeric filler that has some "stretch" to it. Just my $0.02 though - one of the concrete experts on here can probably advise a bit better.