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    Thread: Does LXV Engine (2009-2011 Aveo) Intake Manifold have a PCV Valve? Plus P0171 Blues

    1. #1
      What's wrong with my car?
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      Does LXV Engine (2009-2011 Aveo) Intake Manifold have a PCV Valve? Plus P0171 Blues

      Hi everyone,

      I am Oscar, and this is my first post. I am a long time lurker, but now I find myself with a question that I cannot find any information about, and I am wondering if anyone here knows anything about it.

      I want to know if Chevrolet Aveos with LXV engines (2009-2011 models) have intake manifolds that contain a PCV valve inside of them, that when bad, can cause a vacuum leak and premature deterioration of the valve cover?

      https://www.youtube.com/watch?v=kqvBSK2tluk demonstrates how some Chevy Cruze models have a PCV valve INSIDE the intake manifold that when bad cause a vacuum leak and deterioration of the valve cover. Note how that model also has a PCV valve inside the valve cover, so it has 2 total. At first I thought this didn't apply to my car (2009 Chevrolet Aveo LT), but then I saw https://www.youtube.com/watch?v=_mQ6i4UUy-Q . It is a Chevy Cruze of the previous generation, relative to the one from the link above. That valve cover is IDENTICAL to the one on 2009 Aveo, and all other LXV engine Aveos. It has a PCV valve inside the valve cover, and now i want to know if there is a PCV valve inside the intake manifold too. Afterall, each of the previously mentioned vehicles has an "Eco-tec" engine (when we all know "Cheapo-tec" is more appropriate).

      BELOW EXPLAINS MY P0171 BLUES THAT CAUSED ME TO WONDER THIS ABOUT THE INTAKE MANIFOLD

      I have been fighting a P0171 that occasionally comes on.
      On a cold start, the LTFT stabilizes to a normal LTFT value (between -3 and 10) when parked and the transmission is first switched from Park to Drive (initial cold start stabilized LTFT value temperature dependent, closer to -3 when it is cold outside, closer to 10 when it is hot outside). Then the LTFT's increase as the engine temperature increases. When the car has been running for a good 30 minutes, the LTFT will maximize at 29.7, at idle, if it is hot outside and the P0171 code may get set. The LTFT does stabilize at lower values as the value of engine load and rpm increase for all engine temperatures. The last statement makes me think a vacuum leak, but I have smoke tested my car's air intake and valve cover and found no vacuum leaks, now I suspect the problem to be in the intake manifold, if it has that pcv valve, and want to see if anyone knows whether the Aveos with LXV engines have intake manifolds with PCV valves in them.

      To address the occasional P0171 I have changed:
      1) Air intake ducts connected to the MAF,
      2) the MAF (an AFTERMARKET ONE, maybe this could be it too),
      3) Valve Cover + gasket,
      4) Exhaust manifold Gasket (the maniverter and the flex pipe both looked good and had no holes),
      5) upstream and downstream O2 sensors,
      6) spark plugs and ignition coil boots, and
      7) Fuel pump.
      Changing 1) got rid of the constant P0171 my car initially had, but changing 2) - 7) has done little to nothing to address the issue of the LTFT increasing, for the same RPM and Load, when engine temperature increases.

      I'm wondering if my intake manifold has a bad PCV valve that is causing the LTFT to increase with engine temperature.

      Thanks everyone for reading, I hope to hear back from some of you. If I end up changing the Intake Manifold I'll post what effect, if any, it has on the fuel trims.



    2. #2
      What's wrong with my car?
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      Update:

      I replaced the Intake Manifold. No significant fuel trim change. On a side note there was a ton of blowby that came out with the intake manifold once I removed it.

      But, I was able to resolve the P0171. The problem was with the aftermarket MAF. Once I installed a brand new OEM MAF, the fuel trims are within +-5 at all times, engine hot or cold. It does tend to run between 0 to 5 when the engine is hot and between -5 to 0 when the engine is cold.

      Advice on diagnosing P0171: Take your car for a drive. At idle, if the fuel trims maximize (29.7 for 09 aveo), and at constant 2500 rpm your fuel trims stabilize at or below 10 (check link at bottom claiming a fuel trim above 10 is lean), then you likely have a vacuum leak. If your fuel trims at 2500 rpm are ever high, like mine were (20+ at 2500 rpm with the engine hot), and you have checked for vacuum leaks and find none, then there is likely some other problem, like a sensor problem. IMO the past sentence applies even if your fuel trims maximize at idle, just as mine did with the engine hot.

      Theory on what went wrong with aftermarket MAF: 09-11 aveo MAFs read both the MAF and IAT values. I think the IAT value was more representative of the temperature of the sensor itself rather than the intake air. On a hot, humid summer day in Houston (97 F, 100% humidity), the IAT reading was 42 C=107 f when I started the engine for the first time (it had been resting overnight and morning). The LTFT stabilized at 12 (Already lean! Just safely below the threshold of 29.7 to set off P0171) immediately upon the Fuel System entering into Closed Loop from Open Loop. After driving the car 8 miles, 5 on the highway, when my car was at idle, IAT 55 C=131 F. The LTFT at this point would stabilize at 25+. If I turned the car off in such a state, let it sit for 30 mins, and then started driving it again, the fuel LTFT at idle would first stabilize to 29.7, set of a P0171, and the IAT would be around 64 C= 147.2 F. Once I started driving the car again, and I increased the rpms, the IAT would decrease to around 55 C. I felt the MAF sensor a few times before starting up the engine while hot, and the MAF sure did feel like it was at around 150 F! However, on cloudy, or cold days, the LTFT would still be above 10 with the engine hot, but at idle LTFT would be at 14, and on the highway LTFT would be around 7. The IAT values would also be lower. Now that I changed it with an OEM one the IAT readings are definitely lower, they don't seem to go over 55 C. And the fuel trims are +-5 as I said! Good things never last.............

      Additionally the aftermarket MAF reading at idle would vary +-0.5 g/s at idle. I know that doesn't seem like a big deal but between live data frames the MAF reading would vary from say 3.42 g/s down to 3.01 g/s. I also noticed that the MAF reading would vary more if I had the AC on, which is important to note as cars intake more air when the AC is turned on. So maybe there was something more going on than just an IAT misreading. Now that I changed the part, at idle the MAF reading varies around +-.1 g/s.

      TBH I think that particular aftermarket MAF would be OK for colder environments (car would def run a little lean though), just not hot and humid Houston, TX. I would have to recommend getting an OEM MAF though; who knows how other aftermarket MAFs will behave.

      All that time and money wasted when it was the aftermarket MAF LOL. At least I learned a fair deal about car maintenance, replacing parts, and finally have a car that runs normal.


      https://www.aa1car.com/library/what_...unning%20LEAN.


      Last edited by OscUd; 07-25-2020 at 02:09 PM. Reason: Fixing typos

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