Looking for ranges on Fuel Trims and Ignition timing

[2001ZR2]

Have Wifi OBDII BAFX 327ELM scanner I use with my iPad. Using the DashCommand software

Trying to figure out what is going on in my 1997 Suburban with a 5.7L Vortec, 3.73 gears, 4L60E and LT265/75/R16 rig.

My mileage is horrible in the range of 10-12 mpg so I am looking at the fuel trims and timing to find a clue on where to look next.

The STFT (short term Fuel trim) will vary from -7 to +7 but at a stable speed settles in around -3 to +3 the LTFT (long term fuel trim) will peg at 9.4 and will vary downward as the engine load varies.

Things I wonder about is the Original Ignition coil but the secondary resistance is about 6.5 kOhms. I will check the primary resistance again as I had it on the wrong scale. The ignition control module is also original. The truck has 309k miles.

I also wonder about the fuel spider which is why I checking the fuel trims.

Things I have done without really changing the mileage...New Magnaflow cats and y pipe, Mangaflow muffler and cat back, new spark plugs ACDelco Iridiums (old ones had gray from fuel additive but not bad) and new ACDelco. Replaced the PCV and tubing. Yesterday replaced the air inlet hat at the throttle body as the clip had disappeared.

Also cleaned the throttle body and EGR Valve with a new gasket.

Checked the vacuum and have just under 20 inches at idle.

Cap and Rotor are not that old at less than 2 years. Fuel pump is also less the 20k mileage usage.

Trying not to use the parts cannon but are those fuel trims reasonable?
and I see +33 timing on the highway.

Almost forgot the coolant temp goes up to 194 F and stays there.

 

[RawbDidIt]

That's not too bad. I get the same fuel mileage depending on how liberally i use the happy pedal. Fuel trim at steady rpms should be between positive and negative 5%. Long term is indicative of long term problems, shouldn't be seeing changes while testing for a few minutes at a time. Short term is only indicative once the o2 sensors are at the proper temperature, so wait until you see readings from the o2 sensors before recording stft. Preferably, you'd wait until the engine is at full operating temp. Between positive and negative 7% is could be indicative of a few things, if ltft and stft isn't giving a steady reading positive or negative, it's more or less correct. The ECM constantly adjusts fuel trim based on performance and the task you're performing. If you're fluctuating with 0 in the middle, it's likely not vacuum, fuel, or exhaust related. I'd check compression, see if that checks out.

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[1998crewcab]

a lean air fuel ratio?
long term is concerning ,when replacing those parts if you had a tear/damaged gasket/seal , would had begun to lower you LTFT ( correcting for extra air that was bypassing MAF)

I cant answer the spider question...I have a 7.4L
any oil leaks around intake manifold, valve covers, oil fill seal ? oil leaks are vacuum leaks. might want to pay and have you system smoked.they can check your MAF at the same time to make sure its reporting correct data vs the mismatch the ecm is adding fuel to LTFT to achieve stoichi.
..you have no check engine light on yet....
dont waste your money throwing parts at it, do the simple stuff first. my truck is also aging and I dont drive it a bunch is real hard on seals...
feel free to chime in and correct me if I am wrong please...