lack of power and no check engine light - Page 2
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Thread: lack of power and no check engine light

  1. #11
    madmader is offline [OP]
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    Gen 1... I didnt have enough time to do a wet test last night. Just want wanted to know what they were.
    2016 Cruze LT - needed a motor @ 69K Miles (broken piston ring lands) Currently @ 133K
    2008 Grand Cherokee - 170K and still going strong
    2002 S10 4.3 - 143K and going good as good as new
    1985 Harley Sportster 1000 - 17K and an awesome ride....

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  3. #12
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    Quote Originally Posted by snowwy66 View Post
    170 is what people are posting.

    The engine needs a 11.5 piston to hit close to 200.
    I mentioned that most people don't notice a difference till below 165psi.

    You don't need an 11.5:1 piston to to hit 200psi compression. The 9.5:1 supercharged LSJ 2.0 ECO routinely hit 200psi cranking on healthy engines. Compression readings are affected mostly by temperature,stroke, rod length, and valve timing.

    GM spec for the 1.4 is 174psi minimum. (174-203psi nominal is what they specify for a good test.)

  4. #13
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    Quote Originally Posted by snowwy66 View Post
    170 is what people are posting.

    The engine needs a 11.5 piston to hit close to 200.
    I mentioned that most people don't notice a difference till below 165psi.

    You don't need an 11.5:1 piston to to hit 200psi compression. The 9.5:1 supercharged LSJ 2.0 ECO routinely hit 200psi cranking on healthy engines. Compression readings are affected mostly by temperature,stroke, rod length, and valve timing.

    GM spec for the 1.4 is 174psi minimum. (174-203psi nominal is what they specify for a good test.)

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  6. #14
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    The engine isn't running. Therefore no active turbo to increase compression. Nor any of the other stuff.



    Compression ratio X atmospheric pressure + atmospheric pressure + atmospheric pressure = compression pressure

    You need 11.5 at sea level to get close to 200

  7. #15
    Learning about my Cruze Champagne Jam's Avatar
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    Mechanical issues, ie. Chain jumped or stretched. Plugs. Compression down or uneven. Those issues don't just come and go. No cel light so I am not thinking sensor issues. I'm leaning toward fuel problems. Pump, filter, regulator, any screens clogged. Have you done a pressure check?

  8. #16
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    Quote Originally Posted by snowwy66 View Post
    The engine isn't running. Therefore no active turbo to increase compression. Nor any of the other stuff.



    Compression ratio X atmospheric pressure + atmospheric pressure + atmospheric pressure = compression pressure

    You need 11.5 at sea level to get close to 200
    Nope

    Youre forgetting that air is a gas, and when you compress gas it increases it's temperature. The increased temperature makes a gas expand, which further increases it pressure. The rate at which this occurs varies, but a factor of 1.4 is typically accepted.
    (10.5x14.7) x 1.4 = 216
    Then factor in valve timing and any losses through ring and valve sealing gets you down to GMs 174-203psi

  9. #17
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    Quote Originally Posted by Ma v e n View Post
    Quote Originally Posted by snowwy66 View Post
    The engine isn't running. Therefore no active turbo to increase compression. Nor any of the other stuff.



    Compression ratio X atmospheric pressure + atmospheric pressure + atmospheric pressure = compression pressure

    You need 11.5 at sea level to get close to 200
    Nope

    Youre forgetting that air is a gas, and when you compress gas it increases it's temperature. The increased temperature makes a gas expand, which further increases it pressure. The rate at which this occurs varies, but a factor of 1.4 is typically accepted.
    (10.5x14.7) x 1.4 = 216
    Then factor in valve timing and any losses through ring and valve sealing gets you down to GMs 174-203psi
    10.5 14.7 + 14.7 + 14.7 = 183.75 is the mathematical equation. And I believe we have 9.5. Which puts it more inline with the 170 people have posted.

    The actual math taught in class is

    CR X AP + AP = CP. But the actual number always comes out with an extra +AP.

    Increased temp wasn't even discussed.

  10. #18
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    Quote Originally Posted by snowwy66
    10.5 14.7 + 14.7 + 14.7 = 183.75 is the mathematical equation. And I believe we have 9.5. Which puts it more inline with the 170 people have posted.

    The actual math taught in class is

    CR X AP + AP = CP. But the actual number always comes out with an extra +AP.

    Increased temp wasn't even discussed.
    I don't know what class this was taught in, but it's not the actual equation. It's somewhat close guesstimate, but it's not right. The fact that the number just "always comes out with an extra +AP" for some reason is the first clue it's inaccurate, the second is that the instructor never discussed additional heat. The additional heat is kind of a big deal...**** it's the only reason diesel engines work, and it makes a notable difference in the output.
    Where do these "extra" APs come from? This isnt magic.
    plano-doug likes this.

  11. #19
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    Quote Originally Posted by Ma v e n View Post
    Quote Originally Posted by snowwy66
    10.5 14.7 + 14.7 + 14.7 = 183.75 is the mathematical equation. And I believe we have 9.5. Which puts it more inline with the 170 people have posted.

    The actual math taught in class is

    CR X AP + AP = CP. But the actual number always comes out with an extra +AP.

    Increased temp wasn't even discussed.
    I don't know what class this was taught in, but it's not the actual equation. It's somewhat close guesstimate, but it's not right. The fact that the number just "always comes out with an extra +AP" for some reason is the first clue it's inaccurate, the second is that the instructor never discussed additional heat. The additional heat is kind of a big deal...**** it's the only reason diesel engines work, and it makes a notable difference in the output.
    Where do these "extra" APs come from? This isnt magic.
    Let's stop and think about this.

    We all know atmospheric pressure and what air weighs.

    Now figure out your compression ration. TDC to BDC. The amount of volume area from the top. Increases 9.5 times to the bottom. In our engines.

    9.5 x 14.7. There's no other way to look at it.

    Even though the actual results are always higher.

    And the classes were college, Ford, gm.
    Last edited by snowwy66; 06-13-2019 at 10:10 AM.

  12. #20
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    There's absolutely other ways to look at it...And you have to look at it that way....

    The reason it's always higher than just static compression ratio x atmospheric pressure is because heat is generated.

    If heat wasn't generated by compression diesel engines wouldn't exist.

    Take a tire...With 35psi in it...Drive down the road. The pressure goes up. Heat.

    Put a kettle on stove. It build pressure and whistles..Heat.

    Pressure cooker...Builds pressure, heat.

    Put a balloon in the freezer, it shrinks...It lost heat to the freezer and it's pressure went down.

    You apply heat to a sealed system with air in it and it's pressure will rise.
    You compress the air in a sealed system and it's pressure goes up. Pressure goes up, heat goes up.

    That class did you a disservice by not going any further into the physics of how/why an engine works

    Your equation is basically a version of Boyle's law, with some fudge factor built with those two "extra APs" from out of nowhere. You need to know that Boyles law alone isn't how this is figured out, you need to take into account Charles's, and Gay-Lussacs to be able to actually calculate what's happening. All three of these equations come together to for the Combined gas law. Look at the equation and youll that there's 2 volumes, 2 pressures and 2 temperatures involved. And they are all related to each other. You cant just forget about one or add in extra of another.
    Last edited by Ma v e n; 06-13-2019 at 11:33 AM.
    plano-doug likes this.

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