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Discussion Starter #1
Howdy everyone,
My friend's 2007 Cobalt A/T recently began making what she described as a loud growl from the engine while she was out for a drive. While attempting to limp the car home, it apparently would stall at idle.

I took a look at it in the hopes it was something simple like a bad serpentine belt or seizing accessory pulley, but that whole assembly appears fine, although the serp belt is a bit worn.

The noise is a loud knocking from the cylinder head area that increases in pitch/intensity with engine rpm, and appears to be coming from every cylinder.

To me, it sounds like the timing is REALLY off and the engine is knocking. Engine had oil, and no idiot lights on. Going to run codes tonight, but in the mean time I thought I would ask the experts here what they think it might be.

Thanks in advance
 

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How is the coolant level? Sounds like she spun a connecting rod bearing.
 

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Thanks for the response. Coolant level was fine, and not milky or oily. No obvious coolant or metal in the oil either.

Any other tests for bearing problems?

The noise was more of a rolling knock and seemed to be loudest at the spark plug, which made me suspect a timing issue.

I see no readily visible timing marks or obvious cam angle sensors - is there a way to check timing on this engine using a light? I think it's the 2.2.

Apologies, I'm used to working on older cars with distributor ignition. My wheelhouse is really 80's Volvo and Toyota 4 cylinders.
 

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To check timing you have to remove the valve cover and look at the marks on the chain and cam sprockets to make sure they align. The 07 came with a weak timing chain tensioner. Everybody I know with these I warn to upgrade to the "B" version tensioner, pay a bit now or pay much more later.

 

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Cool. That would be with the engine at TDC I'm guessing.

My fear is that the tensioner has failed and the chain has skipped just enough teeth that the engine will run, but detonate.

I will run error codes tonight to rule out a bad knock sensor. Thanks again.
 

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It can jump one tooth without damaging the valves and still run. But 2 is a disaster.
 

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Ran codes on the engine and got a P0326 - knock sensor.

Could a failed knock sensor cause the engine to retard timing enough to cause knocking, or is this code a symptom of a huge mechanical problem?

I'm hoping this is just a bad sensor. Where do I go from here?
 

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Update - replaced knock sensor, no joy.

Removed valve cover, inspected chain, no obvious damage, but some wear on the side of the chain. Removed and inspected the tensioner, cleaned it and replaced it.

Did a compression test to see if valves were bent, had good numbers (all above 190).

Engine still knock-y.

Anyone have ANY ideas on how to proceed? I don't want to just buy a used engine to drop in unless I have to.
 
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