"You do know your manual is going to be just as useless after a CME or EMP, right? It's got all the same engine-control computers"
Uhh, my diesel greasecar has zero computer controls, zero electronics. Even the switchover from grease to diesel is manual, the tank heater is battery + potentiometer + heating coil + fuse. Not everybody is using modern garbage like you, and those of us not using it are more likely to be able to get our vehicles running.
Example. I've got hot trays from the 1950s. No electronics. They will work direct from AC or DC. EMP proof.
Hot trays today? Good fucking luck. Everyone and their mother insists on putting some sort of digital controller in there. Those won't work after an EMP, either.