I have a 2001 4.8 with 114,000 mi and for the past few yrs ive been getting like 14-17 mpg. I removed the maf screen, but i dont know if that was when it started. I was wondering, i have the stock 02s, do they gradually go bad, or do they just all at once quit. I know it prolly would be a good idea to get new ones, but thats a good bit of cash and i dont want to buy some if thats not the prob. By the way i do have a ses light, i went to a shop and they said it was the rear sensor, but he said the readings were right on it. Could it be a nicked wire? What do yall think?? Oh yea now i have rear 02 sims and i reset the computer, and i still get ses. Anyway somebody help me out here!!!

Thanks,
Derek

 

The rear O2 sensors wont affect fuel economy, but the descreened MAFS can. Your truck has the 85MM MAFS from the factory and is fine well beyond 500 hp, descreening isnt needed.
If this MAFS can support 350 rated hp in the LS1 Vette(360-380 real hp), or 405 rated hp in the 2004 ZO6 (425-445 real hp) it wont restrict airflow in the 4.8L engine.
The LT4 engine was also underrated at 330 net hp @ 5800 rpm., but was dynoing at 360-370 hp thru a 75mm screened MAFS which is 10 mm smaller than yours.
I will never mess with a MAFS again.


Your O2 sims are malfunctioning or a wire is off.
I'd rather tune out the rear O2's rather than use O2 sims IMO. Jesse can do that for $70 along with a full PCM tune. He is the cheapest, but any PCM tuner can do this.

I would get: a new Bank 1 sensor 1 and O2 sensor and a new Bank 1 Sensor 2 O2 sensor (just get new precat O2 sensors). You have enough miles on the originals. Just think of the total volume of exhaust gas that has passed overthose O2 sensors since the odometer read 0, a whole lot.

peace
Hog