This is topic What causes knock? in forum Tech Talk at Northern California Ford Owners  .


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Posted by x2kstangx (Member # 1251) on :
 
For some reason, my car was knocking pretty bad at low rpm when the weather was hot(90-100 degrees). What could be the cause of this? Knocking never happens during normal weather conditions.
 
Posted by QwikStang (Member # 2933) on :
 
I was getting the same thing. A really loud pinging, especially going uphill. I was thinking that my timing was off.

anyone know why it does this?
 
Posted by Blown GR40 Mystic (Member # 476) on :
 
cheap gas or timing is off. also may need a tune-up
 
Posted by x2kstangx (Member # 1251) on :
 
i heard and felt it going to the car show up that damn hill! could it be anything else that causes this?
 
Posted by Sean90GT (Member # 33) on :
 
It's a combination of the heat we've been having, your timing setting and the grade of gas that you are using.

Your car is pinging, which is also known as detonation. Your car is running hotter than normal because of the weather. Lower grades of gas (87 octane) are more volatile and will ignite at lower temperatures. So, when you are running hotter your gas is pre-igniting and this causes the knock (which is BAD for your motor). Basically the air/gas mixture is combusting before the piston has reached the top of its compression stroke. The combustion is pushing down on the piston while the crank is still trying to push up on the piston. You noticed it on the hill because the motor was under a heavy load lugging up the hill.

In the hotter weather either back your timing off a couple of degrees or run one grade higher fuel. Some people also suggest running a little cooler thermostat but I'm not a fan of that.
 
Posted by x2kstangx (Member # 1251) on :
 
I only run 91 octane so i will bring the timing down a bit. Thanks!
 
Posted by 1 FLy5O (Member # 2425) on :
 
a bad ass exhaust leak...i got one right now..goin to rip it apart 2morrow when i get my new gaskets
 
Posted by x2kstangx (Member # 1251) on :
 
i noticed that the inside of my car has been smelling bad lately... and i have tailpipes! shit, i guess i have to go through my whole car with a fine toothed comb.
 




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