98 Tahoe 5.7 OBD II STFT/LTFT

So I'm using way more fuel than I should be in my Tahoe. I went from 15-17 mpg/hwy down to 9 almost instantly.

I did a RT data with my Innova 3160 D which has the OBDII, SRS, ABS abilities, so it not a harbor freight cheapie.

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These are my numbers. What I want to know is, what are normal STFT and LTFT numbers for a 5.7 vortec with less than 70K on the motor.

It has a rough idle, I tried the IAC valve and it didn't make a difference.

I am showing both bank sensor 2s at 99%, but can't figure out why it is so high with all my other numbers looking ok.

I have changed out the CC twice (now it has a complete flowmaster system from the manifolds to the exhaust tips), the O2's twice, Distributor twice, Fuel pump (it needed it anyway), MAP, MAF, plugs, wires, coil, ECM, injectors, I have no SES light on, and compression test is all cyl are within a couple of lbs, all being above 100psi. the engine doesn't knock, and it recently started to use a little bit of oil, maybe 1 qt every 5k miles. I only use Mobil 1 5/30 synthetic and WIX filters.

I am at the point that if I don't figure it out soon, I am going to invest in a gallon of kerosene and a book of matches!!!

Can anyone see what I'm not? It's frustrating because I really love my Tahoe, but cant justify spending anymore money on it.

I am learning here as are most of us are but I see bank 1STFT is 99.2 vs. bank 2 STFT is at -1.6. Not experienced with your scanner but at a glance, this looks suspect. Can you confirm these readings?

I can't see the pics you have on Photobucket, sorry....

Those trim numbers sound weird, I've never encountered a fuel trim of 90% on a 98 Chevy. (I think the highest I've seen is 25%-30% correction. This is usually well within the threshold of code set criteria, so I would expect a CEL).
Typically, we add the LTFT to the STFT to get an idea of total trim. If this number is +/- 10%, it's considered to be in the "normal" range. Fuel trim will vary with engine load and rpm as well. It's useful to check at idle, 2500 rpm and at cruise (if safe to do so).

If the o2 sensors are pegged at over 0.9v, they're telling the PCM that the mixture is rich, and I would expect negative trims to counter this.
Maybe try uploading the pics to the forum so we can get a better idea what you're dealing with .

Those b(1-2)s2 numbers are a default for no input on cheaper scan tools they don't mean anything and you can ignore them . I assume all your readings are at idle that's likely not where your consuming to much fuel have an assistant road test while you monitor live readings at a steady throttle and post back the results

Ben wrote: Those b(1-2)s2 numbers are a default for no input on cheaper scan tools they don't mean anything and you can ignore them . I assume all your readings are at idle that's likely not where your consuming to much fuel have an assistant road test while you monitor live readings at a steady throttle and post back the results

that makes sense, thanks Ben!

I will do that this weekend. And yes, my high fuel use isn't at idle that I can tell.

Not familiar with how to add photos direct, but I'll try again.

Might also check to make sure the brakes are all nice and free it doesn't take much drag to kill fuel mileage you should be able to rotate the wheels freely and they should continue to rotate after you stop turning them(the rear is a little more work because your turning the gears )

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i dont have any wheel issues, and that wouldn't explain my rough idle in park at 700 rpm.

thats the part that is driving me nuts is there is no code, no vacuum leaks, or any other common symptoms of misfire.

I bought new plugs and wires last night, I am going to install them today and see if my idle cleans up.