What are these codes really telling me?

[Bill O'Rights]

My CEL comes on, on my '94 XL, when the engine is under load. Meaning, at highway speed, or when pulling a hill. I purchased a EEC-IV code reader ('cause Auto Zone won't test vehicles that old) and came up with the following codes;

543 O,C Fuel pump secondary circuit fault
186 C Fault in injector pulse width circuit / high

Now...my stupid question is...what's broken? What is it, exactly, that these codes are telling me to fix?

 

[MrShorty]

Which set of codes was the 543 from, KOEO (1st set output during the KOEO test) or CM (2nd set of codes)?

Codes by themselves don't, "tell you what to fix." SOP when diagnosing codes is to start with KOEO codes (hence why I asked if the 543 is KOEO or CM or both)? KOEO codes represent faults that exist at the time of the test and are almost always electrical.

A 543 indicates a fault in the fuel pump circuit. A KOEO indicates that the fault is present right now. A CM 543 without a KOEO 543 indicates an old fault or intermittent fault. Diagnosis would involve inspecting the fuel pump circuit (relay and inertia switch make good starting points) for breaks/loose connections..

CM 186 is related to fuel control. It suggests that the O2 sensor was reading too lean. I would probably focus on the fuel pump codes, as a problem in the fuel pump circuit could easily effect fuel control.