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tjdrury

Causes of Spark Knock?

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Hey all,

I've been experiencing spark knock almost all of the time while driving my car lately. The car has no excessive load in it, the temp outside has been in the 80's, good (91 oct) or bad (85 oct) gas doesn't affect it. I've noticed it before, but only on steep grades or loaded down with cargo. Any ideas:confused: ? Thanks,

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check your timing. I dont know what the timing is supposed to be for sure, but i think its somewhere between 8 ans 12 deg btdc on the N/A subarus. Also try running a higher octane fuel and see what happens.

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First of all, make *sure* your car isn't running hot.

Knock is too much advance on the ignition timing, or an overheating engine.

Carbon build-up in the cylinders can also cause pinging.

Other things can sound like knock or ping also. For instance, a small pinhole exhaust leak, mis-adjusted valves, or loose connecting rods.

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yeah... checking exhaust is a good thing to do. also, might want to check the O2 sensor... if it's bad, things run funny.

 

I replaced cap and rotor, spark plugs, and wires (spent $20 on wires, $10 on plugs, and $12 on cap and rotor) replaced exhaust gaskets, cleaned the EGR valve, and replaced the PCV valve. it's quieter, the muffler sounds more, and way better performance/gas mileage.

 

It might be too much to do, but it might be the best bet. replace EVERYTHING that might do it outside of internal engine work.

 

~jon

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I've also heard that if you put about 2 quarts of diesel fuel in your tank, it helps clean out the carbon buildup on the valves and on the tops of the pistons. Your "knock" or also known as pinging can be caused from: carbon buildup inside the combustion chambers, the timing might need to be adjusted, or like Jon said, your O2 sensor, cap, rotor, wires or plugs might be bad but thats all tune up stuff and its good to replace them all at once.

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