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Discussion Starter #1 (Edited)
I am still chasing the cause of very poor fuel economy. It's been around 10 MPG around town for a few lat years. Throwing parts at the problem (new O2 sensors, etc.) did not help. A crack on exhaust manifold seems to be a common problem causing among other things a poor fuel economy.

Where are the most common areas of such a crack on the passenger side exhaust manifold? Is the crack on the side facing the engine or on other other side? Any way to make a cut out on the shield to see if there is a crack behind. Taking everything apart just to see id there is a crack is too much for me at the moment.
 

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A length of heater hose to ear will reveal exhaust leaks(s) quickly and easily.
If it’s bad enough to cause that poor MPG should easily be able to hear it.

A laptop and scan software also invaluable.

Common for CTS to give bad temp data(too cold) to pcm, engine runs pig rich, mpg goes to hell.
 

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I agree with babywag and the heater hose for finding the exhaust leak.

I don't recall exactly where my original 9C1 manifold cracked, but it was behind the shield and not easily visible, but was easily detected with a piece of hose to the ear.

As an FYI, if you need a new one, I have some, as I bought a new replacement when I found the cracked one on my ride.
 

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Discussion Starter #4
I'll try the hose trick when I find a piece long enough. Thank you.
 
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