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OnlineHelp, Mechanic
Category: Car
Satisfied Customers: 3423
Experience:  Mechanic
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what could cause a loud knocking noise on a 2004 mazda rx8..

Resolved Question:

what could cause a loud knocking noise on a 2004 mazda rx8.. it makes the knocking noise when its idiling and as i drive u can faitly hear it
Submitted: 7 years ago.
Category: Car
Expert:  OnlineHelp replied 7 years ago.

Hello and thank you for choosing Just Answer.


Is it a constant knocking sound?


Does the car shake ?


Do you have power loss?


Did the check engine light come on?



Customer: replied 7 years ago.
yes its a constant knocking noise and yea the car shakes only when its in drive and im stoped umm it dont seem to have any power loss and yes the check engine light actually came on today
Expert:  OnlineHelp replied 7 years ago.

Thank you.


You need to put the car on a scanner and find out why the light came on. Take the car in to a parts store and ask for an OBDII scan. They will run the scan free, which will tell you why the light came on.


Most of the time this is caused by a bad spark plug wire. The wire will slip off the plu and make a knocking noise.


I would make sure all the spark plugs wires are on good. Pull them off and put them back on. Then turn the car on (when it's dark) and open the hood, look for any blue electric arc shooting out. This would indicate that the wire is broken.


Finally, if the light is on for a misfire (the code will be P030#, last number depends on the cylinder) the it's most likely a bad wire or spark plug.



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Customer: replied 7 years ago.

that actually migh be the problem because i just changed the spark plugs a wires myself so they might not be on good... thank you for your help

Expert:  OnlineHelp replied 7 years ago.

Hope that solves your problem.


Good luck!

Customer: replied 7 years ago.
could anything else possible cause the knocing if its not the spark plug or wires
Expert:  OnlineHelp replied 7 years ago.

That scan will be your friend. The fact that the light is on indicates that the car has already found a fault in the system and stored it in the system. Once you do the OBDII scan it will reveal what the problem is. I have a feeling that it's going to be your spark plug wires, however it could also be the knock sensor going off due to low octane fuel.



Customer: replied 7 years ago.
oh ok yea it shouldnt be becasue of low octane fule i only put premium fule in 93 octane... but i will deff do the OBDII scan thank you