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Thread: modded 2008 Solstice 2.0 Turbo running lean at part throttle

  1. #1
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    modded 2008 Solstice 2.0 Turbo running lean at part throttle

    Last year I had a local gentleman show up with a 2008 Solstice 2.0 Turbo and he wanted me to check the state of his tune. He had installed a K&N filter, cat-back exhaust, and had GM flash the Performance Parts 290hp calibration to his ECM. We went on a test drive and everything the scan data showed looked great - no problems.

    This winter he installed a bigger turbo, bigger intercooler, phenolic spacers on the intake manifold, and a high-flow cat. Now his car is hesitating (running lean) during moderate part throttle acceleration (no boost), and the STFT is maxing out at +30% during these periods to try to compensate. At full throttle, there is no problem. At light throttle, fuel trims aren't maxing out but sometimes we are seeing them also drop to -30% during some throttle positions (usually while decelerating).

    When the car showed up here today, it had a P0300 misfire code as well as a slow response code for B1S1 o2 sensor stored in memory. The way the car is running, I can see why these codes would set. But with only having 14k miles on it, I don't see how the o2 sensor could have gone bad already.

    Anyway, HP Tuners does support this calibration but only gives us limited parameters to adjust. I can adjust the MAF calibration table but I don't see anything in there that would allow me to adjust VE. Does anyone know if these ECMs use dynamic airflow calculations and/or VE tables? Basically what I'm asking is will adjusting only the MAF calibration table allow me to fix this fuel issue?

    Has anyone else run into a similar problem before? If so, what did you do to correct the issue?

  2. #2
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    Yes adjusting the MAF table is what you want to recalibrate for the upgrades. The o2 sensor could be bad, but most not likely. If the fuel trims are being maxed out then that is why you are getting a code. Dial the fuel trims in using the MAF Calibration table and see if the codes continue to come back. It is still possible to have a bad o2 sensor.

  3. #3
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    If it has been running rich for a while now, I would recommend to go ahead and install new o2 sensor and new plugs.

  4. #4
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    Something didn't add up in all this. And then I just thought of a possible cause. The owner mentioned something about a spacer that he got with the hi-flow cat that installs between the o2 sensor and the bung. They sent him this spacer with the cat because the company that sells the cat says if you don't install the spacer between the post-cat o2 and the pipe, you can get cat/post cat o2 diagnostic codes that set.

    I asked him where he installed this spacer and he said the instructions didn't say where exactly to so he just put it on the o2 sensor that was the easiest to get to, which sounds like he installed it in the B1S1/pre-cat spot. If he did indeed install a spacer between the pre-cat o2 and the pipe, this would explain the slow response DTC and could also explain this fuel trim / hesitation issue. I'm having him verify where he installed that spacer and told him to remove it if he indeed installed it between the pre-cat sensor and the bung in the pipe. I'll post back when I find out what is going on.

  5. #5
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    Very good thinking on your end. That would be your issue.

  6. #6
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    Just a thought here, but before tuning the MAF you might want to consider a boost leak test. A fixed (small) orifice somewhere in the plumbing may mess with your MAF reading / fuel trims just as much as poorly tuned MAF. All im trying to say is i'd look for a mechanical problem to fix before jumping to blaming everything on the MAF tuning. you did not mention the new hardware updates including a new cold air intake or a MAF relocation, so a new turbo should not affect your MAF that much, at part load. The previously mentioned O2 "spacer" is still a valid concern and first thing to check.

    Someone please correct me if i'm wrong here.

  7. #7
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    Quote Originally Posted by TurboCobalt View Post
    Just a thought here, but before tuning the MAF you might want to consider a boost leak test. A fixed (small) orifice somewhere in the plumbing may mess with your MAF reading / fuel trims just as much as poorly tuned MAF. All im trying to say is i'd look for a mechanical problem to fix before jumping to blaming everything on the MAF tuning. you did not mention the new hardware updates including a new cold air intake or a MAF relocation, so a new turbo should not affect your MAF that much, at part load. The previously mentioned O2 "spacer" is still a valid concern and first thing to check.

    Someone please correct me if i'm wrong here.
    Since he did install a different turbo and intercooler, as well as had the intake manifold off, I am having him check for leaks in the induction and charge air system. You are correct - if there is a leak anywhere between the MAF and the engine, this could certainly throw off the MAF tune - especially since it is a turbo application.

  8. #8
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    The Solstice returned today after the owner moved the o2 spacer from the B1S1 position to the correct location = the B1S2 location. Scan data was much improved (overall fuel trims staying within +/- 7% of zero).

  9. #9
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    Glad you found that. Previous owner installed the same spacer on my front sensor and I had the same issues.

  10. #10
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    I was just reading this...and I have a question. Did he keep the GMPP tune after he installed all these items in hopes that it would adjust itself?

  11. #11
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    Quote Originally Posted by The_Ghost View Post
    I was just reading this...and I have a question. Did he keep the GMPP tune after he installed all these items in hopes that it would adjust itself?
    Not sure what you are asking, but below is a list - in chronological order - of the mods the customer installed as far as I understand it...

    Last year:
    1) High-flow air filter
    2) Cat-back exhaust system
    3) GMPP performance ECM tune

    This year:
    4) Bigger turbo
    5) Bigger intercooler
    6) Phenolic spacers on the intake manifold
    7) High-flow cat
    8) Car was then brought to me to have the ECM tune checked and tweaked

    I don't think there was ever an expectation by the customer that the GMPP tune would be a perfect match for all these mods. I advised him to have the mods installed first, then bring the car to me for a re-tune so we could get the GMPP ECM tune dialed in to work with the new mods.