Mileage dropping steadily

[BigDaddy13440]

Had a crate GM engine from Jeg's put in back in April with some Pacesetter headers, was getting the same 12.5-13mpg I got before I blew the old engine, getting around 340miles on a tank before I refilled (30 gallon tank). Figured the new engine needed to break in before I saw any improvements.

About 5K later, I finally got around to installing the BlackBear ECM I'd ordered, programmed for the EGR delete, rear O2 sensor delete, plans for a CAI, and recalibrated for larger tires (which I don't yet have). Woke up the engine, snappier response, but no gain in mileage. Had codes for O2 sensors prior to the swap, had replaced the front sensors.

Have driven about 8K more on the BB PCM, and my mileage has dropped from the 12.5-13mpg down to barely 11mpg, and I haven't done anything else. What's odd is that my check engine light will be on for a couple days, then off for a few.... then on for a day, off for a week.... then on for an hour, off for an hour.... completely random.

Recently had the codes read, said I was getting codes 0173 and 0175, found this online:

P0173 Fuel Trim Error (bank2)
P0175 Sys too Rich (bank2)

Would it be caused by not having the CAI installed yet? Don't think I need to worry about cold air right now, it's a balmy 4* out right now in NY.

Could the replaced O2 sensors be bad already?

Any other thoughts?

 

[Kon99]

Telling the PCM that the engine has something it does not is a bad idea, so intall your CAI and if your mileage is still dropping come back on here. Let us know what happens, also your o2 sensos could not have gone bad yet unless the wiring is loose which would give an explanation for those codes happening randomly; the wires are bouncing around. Your wires might be the whole problem, who knows.

 

[BigDaddy13440]

Alright then.... CAI on the immediate to-do list, will check the wiring...

Recommendations on a CAI? Volant, Airaid or K&N, or another brand? Pros/cons of each?

 

[SunlitComet]

As stated above but reactivate the egg and two rear o2. Then scan your o2 for bad readings as well as other sensor data.

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