Sudden drop in mpg, 2007 Silverado 1500 2wd classic extended cab WT, V

[rkcharles]

Hi,

The MAF G/s is too high and your STFT and LTFT is all over the place going negative and high positive. Commanding lean and rich. There's your problem. But you also need to check your cat. Your HEGO #2 is not very flatlined. It looks too variable. Check pre-cat vacuum/pressure- no more than +3psi. Is this a flex fuel? Check ethanol content. Rich exhaust will fry your cat.

[Robur]

Hi RkCharles,
Thank you for your reply, I really appreciate it. Could you please clarify a bit for me, in layman terms? How do I check pre-cat vacuum/pressure? The truck is not flex-fuel. I have been putting gas with Octane 87 since 2007( I am in Florida), and the drop in fuel economy was sudden, not gradual. Is there any part that I should replace?

Thank you again.