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Thread: 2010 5.3 highway mileage and power loss troubleshooting

  1. #1
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    2010 5.3 highway mileage and power loss troubleshooting

    I could use some help reviewing my logs to diagnose drivability issue with low power and mpg cruising at 70mph . I have a 2010 Silverado CC 5.3 6-speed 3.42 with 33x12.5R20 tires and a leveling kit, muffler delete, Spectre CAI (dry filter) and 157k miles. Not expecting to win races or get 30mpg but I currently get 11-12 mpg cruising at 70 on flat Illinois highways. I average 13-14 mpg with 50/50 city/highway driving, so it seems city mpg is significantly better than highway. The truck also won't hold 6th gear in the slightest head wind or minor uphill climb. The truck had issues with oil consumption, to the point of fowling the #1 plug every 500-1000 miles. The TSB work to replace the valve cover, soak the pistons and add the oil diverter in the pan seems to have corrected those issues. I am suspecting skewed MAF or O2 sensors but don't want to just throw parts at it. I swapped the MAF with a 2013 truck but didn't notice a difference so I swapped back. Log and current tune are attached. I've done a lot of reading on this and other sites. I have some questions...

    1. Do the LTFT look normal? -10 to -16 at idle and -6 to -7 cruising at 70
    2. Fuel pressure starts at 58 but quickly drops to 43 and stays there, is that normal?
    3. Should commanded EVAP purge be 100% the entire time while driving?

    Thanks in advance.
    Attached Files Attached Files

  2. #2
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    The fuel trims aren't very good. You can easily modify the fuel tables to correct the issue. Or, even better, just reinstall your factory air tube and air box and it'll be much better.

    After you get the fuel trims in order, you might be able to add 1-2 degrees of timing to help with the engine efficiency.

    The 33" tires aren't help the MPG either. It's pretty typical to lose 2-3 MPG when stepping up to a taller/heavier tire like those. They will certainly have more rolling resistance as well. If you're going to run them, make sure you run the tire pressure on the higher side of the recommended specs.

  3. #3
    Tuning Addict 5FDP's Avatar
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    Don't forget about a much wider tread compared to stock, that hurts a lot. If he had 3.73's that would help with staying in 6th gear more.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

  4. #4
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    Thanks guys! I know the tires aren't ideal, and I'm trying to get the owner to switch to a lighter non-M/T tire to save 10-12 pounds per tire even though he wants to stick with the 33x12.5. I know he'll never get the ~20 mpg on the highway like a stock truck, but 11-12 seems really excessive. I should have mentioned these issue pre-date the install of the CAI. The owner of the truck wanted the CAI and an email tune because he liked the way his previous truck ran with those. The CAI and email tune seemed to make no difference in highway driving, maybe a little more seat of the pants feel around town. I went back to the stock tune in an effort to work backwards. I can pull the CAI out and see what happens. Right now, I am running through a tank of gas with the O2s unplugged to see if open loop is somehow better. So far I don't notice any difference. Would stuck piston rings from burning oil result in this kind of power and mileage reduction?

    Also, the speedo calibration still has the stock tire size, but the speedo is dead on with GPS and speed trap radar. Should I run through the gear/tire size wizard anyway and let it adjust the trans parameters?
    Last edited by guff; 05-10-2021 at 07:51 AM.

  5. #5
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    I'd say it's going to get worse gas mileage with the O2's disconnected. But you'll find out either way.

    No need to use the tire/gear wizard if the speedo is accurate.

  6. #6
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    Don't forget to disable virtual flex fuel in the tune. Any filter/air tract change will skew the algorithm and it will think it has like 37% ethanol and dump in fuel. Could be the reason for your fuel trims also.

  7. #7
    Advanced Tuner HawkZ28's Avatar
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    Tune your MAF and VVE. Tweak the trans tables to hold 6th longer up hills. I had issues with the virtual sensor and tuned it out/replaced with a physical kit from Dsteck. Also, check your fuel pressure. I had a fuel pump get weak and cause similar issues.

    My old Sierra CC 4x4 with 275/55/20 tires, cam, headers, MBRP, CAI, SLP UDP, etc etc would only average 14-15 on the interstate doing 75 with 91 octane, 10-12 with E85. Those numbers are with summer gas/temps.

    https://www.fuelly.com/car/gmc/sierr...hawkz28/648160
    Hawk

  8. #8
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    Thanks Hawk. I noticed in scans the fuel pressure starts around 58psi but quickly drops to 43psi when driving and never comes back up, even when idling. I've read various threads where people say 43 is normal, but I don't know what to think of it. Is the scanner pid for fuel pressure accurate?

  9. #9
    Advanced Tuner HawkZ28's Avatar
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    I can't say how accurate it is. I found out using a gauge.

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    Thanks for all the help everyone. I have spent the past few weeks reading this and other sites, watching videos on tuning, and a LOT of time driving, logging, editing and repeating. I spent all my time tuning part throttle VVE and MAF using the fuel trims of the narrow band O2 sensors. I think I have the fuel trims looking much better, but probably far from perfect. I started by disabling flex fuel and setting Stoich AFR to 14.13 for the E10 fuel I have locally. I attached a tune and corresponding log with that as the starting point. Side note, I tried to "split the difference" and use 14.3 but my trims went nuts so I went back to 14.13. The final tune and log are also attached.

    I would greatly appreciate some feedback on the results.

    I also have a concern about some random knock retard. You'll see at its worst around 12:36:30 in the final log. I didn't have KR logged in my early scans but I wanted to start adding timing as @kevin87turbot suggested. I thought the KR was due to a rattling exhaust, but I think I have that fixed and it seems the same. I don't hear or feel any knock when this happens.

    Thanks again, this site is awesome.
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  11. #11
    Tuning Addict 5FDP's Avatar
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    Forget timing if you ask me. It's a stock engine on a stock camshaft still, they only like to run around 20-23 degrees at full throttle and even at cruising speeds when I've added a few degrees I didn't see much change at all.

    In your tune I would disable burst knock. The base vs cyl air delta table set that to all zero's. That might stop some of your random KR jumps.

    Change up your PE settings too. Low the HOT pedal enable to 65%, lower the RPM delay to 1,500rpm, raise the MAP kpa enable to 80kpa. Then level out the EQ ratio so that it's 1.200 from 2,500rpm all the way to red line. The factory runs the calibration a little rich and it's safe enough to run a little leaner around low to mid 12's for commanded AFR at full throttle.

    A few changes to torque mngt and tuning that transmission would make a hell a difference in how it drives too.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

  12. #12
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    Quote Originally Posted by 5FDP View Post
    Forget timing if you ask me. It's a stock engine on a stock camshaft still, they only like to run around 20-23 degrees at full throttle and even at cruising speeds when I've added a few degrees I didn't see much change at all.

    In your tune I would disable burst knock. The base vs cyl air delta table set that to all zero's. That might stop some of your random KR jumps.

    Change up your PE settings too. Low the HOT pedal enable to 65%, lower the RPM delay to 1,500rpm, raise the MAP kpa enable to 80kpa. Then level out the EQ ratio so that it's 1.200 from 2,500rpm all the way to red line. The factory runs the calibration a little rich and it's safe enough to run a little leaner around low to mid 12's for commanded AFR at full throttle.

    A few changes to torque mngt and tuning that transmission would make a hell a difference in how it drives too.

    Thank you for the suggestions. Did you happen to take a look at my logs? Don't want to run this tune if I screwed something up. I will experiment with the changes you mentioned. I'll have to read up on torque mgmt and trans tuning. Any suggestions for a quick tutorial?