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Discussion Starter · #1 ·
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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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.

Sent from my SM-G950U using Tapatalk
 

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Discussion Starter · #8 ·
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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Discussion Starter · #9 ·
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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Discussion Starter · #10 ·
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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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!
Usually just the upstream. The downstream has a small impact, but if it's not swinging around wildly, I'd leave it.
@XtremeRevolution sells a boost leak tester he developed for these cars.
 

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Beyond my tire thoughts, the only other thing I've run across on various makes is a thermostat that is opening too soon at too low a temperature.
The engine, even though operating in closed loop, will tend to run rich in response to the coolant temperature.

Naturally, you are there, I am here, and there is no reader information. I would hesitate to just pitch the O2 without watching its responses, and you will require a reader for that.....or maybe one of these deals where you use your phone to scan.

Rob
 

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Discussion Starter · #13 ·
Beyond my tire thoughts, the only other thing I've run across on various makes is a thermostat that is opening too soon at too low a temperature.
The engine, even though operating in closed loop, will tend to run rich in response to the coolant temperature.

Naturally, you are there, I am here, and there is no reader information. I would hesitate to just pitch the O2 without watching its responses, and you will require a reader for that.....or maybe one of these deals where you use your phone to scan.

Rob
I have the Bluetooth OBDII module with the Torque app. It has the vehicle running what I consider to be very hot, but apparently within the normal range for these engines... 215-225*. I can check out the app to see about O2 readouts but I wouldn't really know what I'm looking at anyway.
 

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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?
Upstream is what controls air/fuel ratio.

Here is a link to one thread at Cruzetalk about the wastegate pivot pin and it has a link to a youtube video as well.
https://www.cruzetalk.com/forum/34-gen1-1-4l-turbo/113913-wastegate-pivot-pin-wear-clearance.html
 

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Discussion Starter · #15 ·
So after about a week of driving with a new upstream o2 and cleaned MAF, I have noticed no changes in gas mileage or performance. I am looking into the boost leak kits now. Does anyone have any perspective on how often these leaks are being found?
 

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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.

Sent from my SM-G950U using Tapatalk
The ECO MT never had the ECM update. It was limited to the automatics.
 

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I have the Bluetooth OBDII module with the Torque app. It has the vehicle running what I consider to be very hot, but apparently within the normal range for these engines... 215-225*. I can check out the app to see about O2 readouts but I wouldn't really know what I'm looking at anyway.
Temperatures are normal for this car.
 

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The ECO MT never had the ECM update. It was limited to the automatics.
Coulda sworn there was one for the later year manual transmission 1.4T's as well. Jerry Lewis mentioned something about it and his later Eco not getting the same gas mileage as an earlier one he had, but don't know if he has an account here.
 

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Discussion Starter · #19 ·
So I just used Xtreme's boost leak kit, which is awesome and dead simple btw. Immediately found a leak at the throttle body connection, which seems to be mostly if not entirely gone by increasing the torque on the hose clamp. However, I found another leak at what seems to be the valve cover. On the top / middle area of the valve cover between the two bolts there is a little bump out (see pics). If I place firm pressure with my hand right on that bump area it stops the hissing. I also see some oil residue down in the gasket area. Is this something I need to address? Can I try increasing the torque on the bolts, or do I need a new gasket, or valve cover?

Thank you!

View attachment 271029 20190506_140042.jpg
 

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Check or replace both o2 sensors ( up and downstream ) and clean
your MAF sensor + intake manifold if you really wanna do it right, if you still have a problem then it’s something deeper unfortunately keep me posted on this!
 
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