The car, a 92 Accord EX Coupe automatic, is throwing Codes 13 and 16:

Code 13 - Atmosphric Pressure Sensor
The PA sensor should read close to the MAP sensor of 2.75v, this may very small amounts due to current weather conditions and elevation. Due to it's location, it is probably easier to check the voltage at the ECU. This sensor vary seldom, or never at all should fail. Flooding may have damaged it, at one time or another.

Code 16 - Fuel Injector
Code 16 is probably the Main Relay, however it could still mean a bad Injector, Resistor Box tho.
Most failures occur, when the weather starts heating-up for the summer...

WHERE would you start if you had to fix these problems?

 

You are on the right track with the code 16. That code will set if there is a break in the electrical circuit for the injectors which includes the Main Relay and injector coils. Your comment about the weather heating up would strongly suggest the main relay as the culprit. The solder joints expand with heat and any hairline fractures may open up enough to break the circuit.

I would start with the main relay first. You can try to resolder the circuit board contacts first if you know how to solder electronic stuff. It's not too difficult. Otherwise I think it's about $40 from the dealer for a new one.