[Blasirl]

2012 1LT 1.4T Auto 223,000mi. Recently had the ECU disable the turbo because of sensor failures. Codes pointed to intake tract. Replaced MAF, MAP and IAT sensors and she came back to life. During the diagnostic processes, I broke down and got the code reader because troubleshooting without them is just silly now. A few long trips after replacing all those sensors, I noticed sluggish performance and fuel economy had taken a dip from around 33-34mpg Hwy to 28-30. I hooked up the code reader and watched the data. STFT and LTFT numbers were spot on, but I noticed that the engine was pushing boost even while going down hills. O2 sensor graphing showed the typical sinusoidal waveform during steady load. I've read that the sensor can behave lazily but appear to be functioning normally which can affect economy and performance. I fear that during the few long trips I took with the wastegate being open did damage to the cat. I suspect the fuel system was running more toward the rich side as a precautionary measure to prevent engine damage due to the sensors not functioning properly and this caused the cat to load up. Once engine performance returned, I wonder if the loaded cat got too hot and damaged the honeycomb mesh inside. Cat temps during moderate load across level ground is around 1200-1300ºF which seems a little hot to me. I have new O2 sensors but I am holding off on purchasing a new cat for now as it is a much more pricey part to just replace without knowing for sure. I feel like 223,000 miles out of the original sensors in the intake and exhaust streams was good life. As it stands at this point, I have put 1400 miles on since new intake tract sensors and engine is not throwing any powertrain codes.

This may sound out in left field, but with that many miles, have you checked the intake PCV valve. I only ask because you mention too much boost and sluggish performance.

2011-2016 Cruze 1.4 PCV Valve Cover/Intake Manifold Issues

 

[Blasirl]

So, I forgot to update this following my diagnostics and repairs I put in place.

I traced my throttle signals through range and during steady state driving and it showed that one of the throttle body channels was throwing bad data which led to increasing fuel consumption when combined with original O2 sensors having a quarter million miles on them. I also had boost leak on the connection to the intercooler which i was losing performance and likely economy to, also.

I replaced the boost hose between the turbo and the intercooler, the throttle body, O2 sensors #1 and #2, and inspected and tested flow through both the primary and secondary cats(hooked shopvac up to one end to see if flow restriction was present). while I was in the engine bay, I replaced the oil supply line to the turbo because the o-rings had gotten aged and started weeping also, although I know that was not affecting performance or economy, just a nuisance leak that was making a mess.

after repairs, I've put around 1,000miles on of my normal driving and I've lost stuttering and stumbling issues at mid-range, gained midrange boost and acceleration, improved fuel economy back to near 33-34mpg, throttle response improved and have no lights, warnings, codes or other indicators of performance issues.

All my data streams are reading favorable numbers and I anticipate many miles of trouble free driving with my batch of mods, repairs, and new sensors all over the engine systems.

This forum has been very helpful for me in diagnosing troubles based on feedback and reading about similar problems so I hope I am successful in paying it forward by providing my experiences with my recent troubles.

K

Thanks for coming back and closing the loop.