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Discussion Starter #1
I am still fighting this issue... lack of power, and no CEL, or even pending codes. and it is hit and miss too boot. sometimes it is fine, other times its not.

Here is what I have done.

1. pressure checked for air leaks...
2. tune up using OEM spark plugs about 15K miles ago
3. New turbo about 5K miles ago
4. New intake 9 Months ago
5. Checked the entire PCV system... all good

I think I am going to do a compression test this weekend...

Ready too just trade it off...

any ideas?
 

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What octane gas are you running? The gen 1 Cruze engines are actually built for 91 octane and it's the ECM software that allows them to safely run on 87 octane. The problem is the ECM throws away a significant amount of power to safely run on 87. Try 91 octane for a couple of tanks and see what happens.
 

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Discussion Starter #3 (Edited)
I have always ran 87 octane in the car and I purchased it new about 3 years ago. The engine has about 87K miles on it. (cracked ring lands in the original motor). It just started doing this about three weeks ago... Honestly, it is starting to act just like the original motor did before it went to complete crap... just not using any oil, yet.
 

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Discussion Starter #4
ok, just did a dry compression test...

Cylinder 1 - 140PSI
Cylinder 2 - 130PSI
Cylinder 3 - 120PSI
Cylinder 4 - 125PSI

Now cylinders 1 and 2 passed 100PSI on the second crank. 3 & 4 was more like the 4 crank out of a total of 5 cranks.

so I am going to say I have two week cylinders, AKA, a junk motor, again..... and only 87K miles on it...

thoughts?
 

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Assuming you're in North America, it's now summer. With the warmer weather, the ECM is going to have to retard spark to prevent knock. That's where having higher octane when under boost really helps. It was the earlier model years that really had problems, but a tank of 92 is a cheap to try.
 

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And you say you tuned it up using OEM plugs. I suggest you remove them, check the gap, ensure it is .028 and torque them to 18ft-lbs - no anti-seize and then make sure the resister springs are free and not caught up in the rubber boot. When you pull the coil pack, check the boots for tracking.
 

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ok, just did a dry compression test...

Cylinder 1 - 140PSI
Cylinder 2 - 130PSI
Cylinder 3 - 120PSI
Cylinder 4 - 125PSI

Now cylinders 1 and 2 passed 100PSI on the second crank. 3 & 4 was more like the 4 crank out of a total of 5 cranks.

so I am going to say I have two week cylinders, AKA, a junk motor, again..... and only 87K miles on it...

thoughts?
I'd agree with you. You've got a mechanical fault. I wouldn't waste anytime with different fuels, or spark plugs or anything.

You should have compression number far closer to 200psi. 165psi is about as low as you can really go and not notice a difference. The 20psi variance is also as you mentioned cause for concern.

You could in theory have a stretched or skipped chain causing low compression, but the cylinder to cylinder variance would still be a death knell. Sorry.
 

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Discussion Starter #8
and the motor only has 87K on it... I have always faithfully changed the oil every 5K. I never "hot rodded" the car either... This is the second motor..... something is not right.
 

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I'd question the gauge itself with those low numbers across all cylinders.

This is a Gen 1? Have you tried a WET compression test (little bit of oil) to see what the #'s look like?

As someone else said, these cars feel completely gutless in the summer on 87 octane. Try a tank or two of 93 and see if it perks up.
 

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Discussion Starter #11
Gen 1... I didnt have enough time to do a wet test last night. Just want wanted to know what they were.
 

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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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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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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
 

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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?
 

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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
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
 

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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
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.
 

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snowwy66 said:
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.
 

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snowwy66 said:
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.
 

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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.
 
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