93 Explorer codes

[Papercut]

I just bought a 93 xlt that runs great and recently passed emissions and evap but apparently the cel was burned out so it failed. After replacing the bulb the cel came on on my way to do the retest. The OBD game me a 543 code. The manual says its a fuel pump circuit open to the ECM. I heard there is a sensor that trips if you get rear ended that disables hte fuel pump? The rear bumper looks like it took a hit of some sort but nothing major, any ideas?

[shorod]

There is an inertia fuel pump switch that will turn off the fuel pump in the event of a significant impact. As you might expect, if this switch opens, the fuel pump stops working and therefore so does the engine. I guess you could verify a previous owner didn't install an inline "booster" fuel pump that is masking a failed stock fuel pump.

Did you buy this vehicle from a car lot or a private party?

-Rod

[Papercut]

I bought it used from a senior man with 146k who maintained it regularly till it failed smog 2 years ago. I doubt if he did any mods to the fuel system. He was told it needed a new catalytic and he did not want to spend 1000 on it. Another code I got was a 172 lean cond o2 sensor. I replaced the upstream o2 sensor but the code didnt clear. I'm hoping its the downstream sensor so I will replace that also. The car runs great but I just can clear these codes.

[shorod]

Is this really a 1993? If so, I doubt it has a downstream sensor. This is where people often make mistakes, a code stating that an O2 sensor is reporting a lean condition does not indicate the problem is with the O2 sensor. Rather, the sensor is reporting a lean condition on the related cylinder bank. Sure, this could be due to a faulty oxygen sensor, but more likely there is probably some thing causing a lean condition. Maybe you have a vacuum leak (intake manifold, maybe) or a fuel injector that is not opening.

-Rod