I have a 95 t-bird with an 3.8 motor the trouble that I am having is when its hot out you can here the motor knock when you are accelerating for a stop.It just does this when its hot out 80 plus out.
Anyone have an idea?

Thanks

 

Sounds like spark knock, more accurately called "preignition".

Causes can be:

Low Octane gas

Build up of carbon in the combustion chamber causing an increase in compression ratio (which leads to the need for higher octane gas).

Build up of carbon in the combustion chamber causing hot spots which serve to ignite the fuel/air mixture before the spark plugs are told to ignite it.

Incorrect ignition timing

Engine running hotter than normal

Spark plugs (wrong heat range or need repalcing)


Those are just the common causes, with little to no explaination as to how and why.


I'm guessing your car is a high mileage vehicle. About the simplest thing you can do is insure proper operating conditions (plugs, air filter, etc) and run a bottle of STP Superconcentrated fuel system cleaner, Chevron Techron, or similar product through a tank of gas. Buy a bottle of the good stuff (about $6 per bottle) and see if that helps. It might help reduce combustion chamber deposits that could be leading to preignition.

Other than that, live with it if it isn't severe, or switch to higher octane gas.

Keep us posted and please post back if you have more questions or comments.

Thanks!

 

Thanks Brian it does have 130k on it but I have put in two bottles of winn's fuel system cleaner and it didnt help so im going to do a tune up with air filter this week end.