Poor gas mileage!
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Thread: Poor gas mileage!

  1. #1
    caddy96sts is offline [OP]
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    Poor gas mileage!

    I need some advice from the community. 2014 Cruze Eco 6M/T. Bought new and babied to 92k. The whole reason we bought this vehicle is for the gas mileage. I hypermiled with it and routinely got high 40's and even low 50's MPG averaged for the first few years of ownership. No problem. We were happy. Then things changed. The last maybe 1.5 years and 20k the mileage has dropped like a rock. I am talking an average of 36mpg indicated, ~34 calculated. That is still hypermiling, with 90% highway driving, cruise locked in at 65. Driving conditions are mostly identical. Tires overinflated. Synthetic oil and trans fluid. Techron every oil change. Premium fuel only since the beginning. New air filter. No check engine lights. No obvious issues. I thought maybe it was the PCV issue, and found that the orange valve was gone. Intake manifold replaced...no change in mileage. In the past year I have done the ignition coil, plugs, intake manifold, and battery terminal.

    It is really frustrating because we bought this car new to keep it for at least 10 years and 200k+ but with such a gas mileage drop we are struggling to justify it. I don't really want to bring it to the dealer and pay just to have them tell me "no problem found".

    Is it worth doing a MAF cleaning? Any other things to check out?

    Thanks in advance!

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  3. #2
    Handbrake Released froyofanatic's Avatar
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    MAF cleaning is easy & cheap and can make a big difference.

  4. #3
    caddy96sts is offline [OP]
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    Quote Originally Posted by froyofanatic View Post
    MAF cleaning is easy & cheap and can make a big difference.

    I will try this tomorrow. I didn't know if there was any point since I figured a dirty MAF sensor would have triggered a CEL?

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  6. #4
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    Do a compression check. Weak compression would cause loss of mileage.

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    What brand, size, and type (meaning low rolling resistance...ie LRR) tires are on the car?

    This, and tire pressure (remember, LLR tires can operate at 51psi) are the most common, non mechanical cause for a mileage loss.

    The analogy I like to use is how easy it is to pedal a bicycle when the tires are correctly inflated......all will admit that rolling resistance changes are amazing.

    Rob

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    After the tires are reviewed, the other thing that could contribute to poor fuel economy is an 02 sensor starting to fail. It is directly used to calculate air/fuel ratio once the vehicle is warmed up. With the tolerances built into the cal for one that is "properly functioning" it may not be triggering the CEL yet, but has deteriorated over time and its response time for lean/rich readings has slowed down. A common item on this vehicle is boost pressure, I would check your linkage on the turbo and make sure the pin hole is not worn out and sloppy. This is a quick and free check to see the condition of it. Many users have commented there hole has been worn out but not setting a CEL due to the ECM calibration GM uses as "acceptable".
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    Clean sensors, maybe replace O2 sensors (relatively cheap on these), and check for BOOST LEAKS - these are becoming pretty common as these things age. Especially around the throttle body hose.

    Did this car ever have the emissions ECM update performed? That caused a fairly significant drop in mileage.

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  10. #8
    caddy96sts is offline [OP]
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    Quote Originally Posted by Robby View Post
    What brand, size, and type (meaning low rolling resistance...ie LRR) tires are on the car?

    This, and tire pressure (remember, LLR tires can operate at 51psi) are the most common, non mechanical cause for a mileage loss.

    The analogy I like to use is how easy it is to pedal a bicycle when the tires are correctly inflated......all will admit that rolling resistance changes are amazing.

    Rob
    So I very recently got new tires Bridgestone RE980AS. I know these are FAR from efficient, especially compared to the LRR options. However, it seemed like the better choice at the time. Regardless, my MPG numbers have been down far longer than I've had these tires. The tires are at 51psi. I would expect at most a 6mpg drop vs the stock LRR. Unless the literature I've read on the topic is inaccurate.

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    caddy96sts is offline [OP]
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    Quote Originally Posted by lonewolf04 View Post
    After the tires are reviewed, the other thing that could contribute to poor fuel economy is an 02 sensor starting to fail. It is directly used to calculate air/fuel ratio once the vehicle is warmed up. With the tolerances built into the cal for one that is "properly functioning" it may not be triggering the CEL yet, but has deteriorated over time and its response time for lean/rich readings has slowed down. A common item on this vehicle is boost pressure, I would check your linkage on the turbo and make sure the pin hole is not worn out and sloppy. This is a quick and free check to see the condition of it. Many users have commented there hole has been worn out but not setting a CEL due to the ECM calibration GM uses as "acceptable".
    I ordered a new upstream sensor. Would it be ok to just do that one for now to see if it helps? Or would I need to do the downstream as well? I understand the relationship between the two.

    The second item you mention regarding the pin hole... I have no idea what you are referring to... is there a tutorial on this somewhere?

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    caddy96sts is offline [OP]
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    Quote Originally Posted by jblackburn View Post
    Clean sensors, maybe replace O2 sensors (relatively cheap on these), and check for BOOST LEAKS - these are becoming pretty common as these things age. Especially around the throttle body hose.

    Did this car ever have the emissions ECM update performed? That caused a fairly significant drop in mileage.

    Sent from my SM-G950U using Tapatalk
    To the best of my knowledge it never received any sort of emissions update. Unless it was done during another service and not noted. I am cleaning the MAF. I ordered the upstream 02 sensor. Do you think they both would need to be done or is the upstream sensor the only one relevant to gas mileage (assuming no CEL)?

    Is there a easy way to check for boost leaks? This is my first turbocharged vehicle.

    Thank you!

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