I am working on an 90' Accord and the CEL came on and I checked it and it flashes a 43 - fuel system supply. I changed the fuel filter, spark plugs, and the O2 sensor figuring that's normally what goes wrong. I put in the Denso O2 sensor seeing as the bosch ones are inferior on imports. The CEL came back on a week later after resetting via negative battery terminal. Same code. The Car runs really sluggish randomly at about 2500 rpm but becomes fine once you depress the throttle a bit more. The fuel economy Is absolutely horrible about 23L/100k. I blew threw the fuel pressure regulator and the diaphragm seems fine. I am thinking either fuel pump or fuel pump relay next :/ Any info would be greatly appreciated! Thanks in advance

 

I got the same code a few weeks ago but it went away on its own.

 

Normally this is oxygen sensor gone bad. If you replace be sure to get Denso not Bosch.

 

I indeed put in a Denso O2 sensor.

 

Although the diaphragm may be fine, the spring may be failing. Check your fuel pressure, and verify the pressure appropriately changes with vacuum change.