[OE812]

I have a 2001 Silverado5.3L automatic with approximately 225,000 miles. I recently noticed a large drop in mpg from 17 mpg in mixed driving to 12 mpg. It does not have any engine codes or engine light lit. I ran live data on the OBDII scanner and have the following. Are these numbers considered normal operating figures?

Air ECT STFTB1 LTFTB1 RPM IAT B1S1 STFTB1S1 OVB1S2 STFTB1S2 OVB2S1 STFTB2S1 OVB2S2 STFTB2S2

65 190 -7.8 0 2052 87 0.68 -14.8 0.1 N/A 0.82 -14.1 0.095 99.2
65 190 -5.5 -0.8 2038 87 0.065 -5.5 0.03 N/A 0.15 -2.3 0.075 99.2
65 190 -10.2 -1.6 2037 87 0.73 -3.1 0.08 N/A 0.825 -10.2 0.14 99.2
65 190 -3.9 -2.3 2068 87 0.59 -10.2 0.105 N/A 0.805 -9.4 0.14 99.2
65 190 -9.4 -3.9 2062 87 0.165 -3.9 0.045 N/A 0.65 -8.6 0.13 99.2
65 190 -8.6 -3.9 2068 87 0.155 -2.3 0.05 N/A 0.14 -2.3 0.075 99.2
65 190 -7 -4.7 2065 87 0.1 -1.6 0.035 N/A 0.055 0.8 0.065 99.2
65 190 -6.3 -4.7 1996 87 0.055 2.3 0.035 N/A 0.16 5.5 0.07 99.2
65 190 -6.3 -4.7 1996 87 0.055 2.3 0.035 N/A 0.16 5.5 0.07 99.2
65 190 -1.6 -4.7 2016 87 0.11 5.5 0.05 N/A 0.88 0 0.09 99.2
65 190 -0.8 -4.7 2042 87 0.845 0 0.13 N/A 0.62 0 0.38 99.2
65 190 -0.8 -4.7 2050 89 0.72 -1.6 0.18 N/A 0.145 6.3 0.115 99.2
65 190 6.3 -4.7 2045 87 0.605 -0.8 0.105 N/A 0.815 0 0.12 99.2
65 190 5.5 -4.7 2067 89 0.84 0 .12 N/A 0.835 0 0.245 99.2
65 190 -0.8 -4.7 2088 89 0.62 -1.6 0.275 N/A 0.44 3.9 0.655 99.2
65 190 -0.8 -4.7 2083 89 0.165 3.9 0.26 N/A 0.825 -3.1 0.795 99.2
65 190 -1.6 -4.7 2111 89 0.2 3.1 0.38 N/A 0.47 2.3 0.69 99.2
65 190 3.1 -4.7 2129 89 0.2 2.3 0.475 N/A 0.77 -3.1 0.5 99.2
65 190 3.1 -4.7 2112 89 0.77 -0.8 0.085 N/A 0.88 -0.8 0.11 99.2
65 190 4.7 -4.7 2149 89 0.83 0 0.165 N/A 0.315 3.9 0.215 99.2
65 190 0 -4.7 2171 89 0.815 -0.8 0.765 N/A 0.805 -1.6 0.715 99.2
65 190 3.9 -4.7 2192 89 0.845 -0.8 0.81 N/A 0.285 1.6 0.735 99.2
65 190 3.9 -4.7 2189 89 0.165 3.1 0.69 N/A 0.455 2.3 0.585 99.2
65 190 3.1 -4.7 2147 89 0.085 6.3 0.105 N/A 0.13 6.3 0.095 99.2
65 190 5.5 -4.7 2148 89 0.82 0.8 0.13 N/A 0.735 0.8 0.195 99.2
65 190 0.8 -3.9 2199 89 0.78 0 0.18 N/A 0.395 4.7 0.36 99.2
65 190 6.3 -3.9 2196 89 0.36 5.5 0.23 N/A 0.755 0 0.17 99.2
65 190 4.7 -3.9 2189 89 0.085 4.7 0.105 N/A 0.12 7.8 0.1 99.2
65 190 6.3 -3.9 2199 89 0.73 0 0.145 N/A 0.755 0 0.165 99.2
65 190 0 -3.9 2196 89 0.165 6.3 0.105 N/A 0.22 5.5 0.14 99.2
65 190 0 -3.9 2217 89 0.775 -0.8 0.215 N/A 0.87 0 0.735 99.2
65 190 -1.6 -3.9 2237 89 0.805 -2.3 0.77 N/A 0.745 -3.1 0.84 99.2
65 190 -3.1 -3.9 2227 89 0.1 2.3 0.64 N/A 0.065 3.9 0.535 99.2
65 190 -1.6 -3.9 2200 89 0.715 -1.6 0.735 N/A 0.855 -0.8 0.815 99.2
65 190 2.3 -3.9 2210 89 0.7 -3.1 0.77 N/A 0.77 -3.9 0.795 99.2
65 190 -3.9 -3.9 2178 89 0.075 3.1 0.15 N/A 0.68 6.3 0.12 99.2
65 190 3.9 -3.9 2205 89 0.83 -0.8 0.18 N/A 0.78 0 0.21 99.2
65 190 -2.3 -3.9 2228 89 0.58 -2.3 0.31 N/A 0.75 -1.6 0.75 99.2
65 190 -2.3 -3.9 2232 89 0.745 -3.1 0.75 N/A 0.425 -3.9 0.77 99.2
65 190 3.1 -3.9 2205 89 0.745 -1.6 0.36 N/A 0.175 3.9 0.13 99.2
65 190 -0.8 -3.9 2212 89 0.205 3.9 0.285 N/A 0.195 4.7 0.15 99.2

 

[Pikey]

The format that data is in or at least how it looks on my phone is impossible to read. Each one should tell us what data you are posting. When was the last time you changes spark plugs and wires? Fuel filter and at filter? O2. Sensors? You can show us the numbers all Lyon want for the O2 sensors, but the numbers don't tell us if they are switching as fast as they should be. Is the engine operating at the proper temp?

I looked at your data again. It is not impossible to read, just hard. There should be commas between each of the categories to separate them

 

[j cat]

with no DTC codes this could be from a restricted exhaust. also air filter restricted.

use some techron injector cleaner . the fuel regulator may be leaking so remove vacuum line to it see if it smells of fuel.
if ignition had problems the dtc will show.

replacing the upstream O2 sensors will help improve MPG when they have 125k miles or more on them as this is the end of life

 

[OE812]

Changed plugs wires at 150000 miles. Changed fuel pump, filter, and fuel regulator at 220000 miles. Changed o2 sensors upstream only at 215000 miles. Also changed coolant temp sensor at same mileage. Lastly I changed knock sensors and intake gaskets last week and engine vacuum is 21 (all ac delco or Delphi parts).

I have an excel document with the scan data but couldn't figure how to upload.

 

[silverado002]

Have you recently purchased fuel from a different station? Or has the fuel blend changed to additional ethanol perhaps?

 

[OE812]

Consistently fill from Shell and every 3rd tank from Chevron with Techron. Both oil companies are on winter blend with 10% Ethanol through Mid-March when the Reid Vapor Pressure (RVP) is adjusted to less oxygen levels. With confidence I can state that it is not the fuel.

 

[j cat]

Consistently fill from Shell and every 3rd tank from Chevron with Techron. Both oil companies are on winter blend with 10% Ethanol through Mid-March when the Reid Vapor Pressure (RVP) is adjusted to less oxygen levels. With confidence I can state that it is not the fuel.

what about the fuel regulator ? check the vacuum line to it for fuel smell............new sometimes is bad.

 

[OE812]

jcat:

Yes I changed the fuel regulator at 220,000 with SMP which didn't give me the 55psi needed as specified. I replaced with the Delphi OEM fuel regulator and now I am getting 55-57psi.

 

[j cat]

so this MPG drop is from after or before the work/parts replaced ?

the 12 MPG is not proper. MPG of 14 in city and 18 on hyway is normal. very cold weather does drop the MPG.
on these vehicles cold air intakes and Throttle Body spacers/coolant mods will drop MPG in cold weather even more.

 

[OE812]

The poor mpg started before the work was done.

 

[j cat]

with the mileage this can be the exhaust restricted. converters or the muffler. being down in a warm area your not in the very cold conditions so this can be the cause.

 

[OE812]

I changed muffler at 215000. What is best test !method for bad cats? Temperature before and after cats or back pressure at the upstream o2 bung?

 

[j cat]

measure the upstream pressure compare the 2 sides should be the same. back pressure should read low. hard so say the exact reading but under 10psi should be good as a very loose #.

another method which I have done is start up cold engine go under vehicle put a hand on each converter. both should get hot the same amount. if one is slow to get hot or not get hot then that one , the colder one , is the problem.