Still messing around with this miss at cruise..

[blowby]

Ok,
If any of you remember, this all started witha 3 month storage issue.
Car would stumble only during cruise conditions. Start,idle, and Accel. were fine.
Was getting 16mpg at best.
Replaced fuel pump, checked regulator.
1yr old Bosch O2's.
Cleaned MAF=major help.
Problem came back.
Replaced MAF with another used unit (cleaned it first).
Now car runs better now, getting 25mpg hwy. at 80mph.
However now I am getting another code and the engine is hesitating again during cruise.

The code is...543
"Fuel pump monitor circuit shows no power - Power / Fuel Pump Circuits"

This is accompanied by both rich and lean codes on both o2's.

Any idea what this code is suggesting?
I can hear the pump running before starting and while car is running.
Idle fuel pressure is good.

Bryan

 

[sdpatt]

With both rich and lean codes on both O2 sensors, your engine is not able to properly meter the fuel. The much higher mileage tells me that the mixture may be unnaturally lean due to that 80mm MAF sensor. You should check for vacuum leaks from cracked hoses and loose intake manifold hose clamps.

If you have a misfire without a CHECK ENGINE light, 99% of the time the causes will be the spark plugs and/or plug wires.

 

[etc1006]

But nobody seems to know the 542, 543 code reasons? My car runs fine with those codes...