When ever i put my foot down more than half way and the revs go up around 3k rpm, the engine gives me a kind of thud repeatily until i stop accelerating or pass 4k rpm. Also, when i downshift and pass by this rpm range it does the same. This does not happen when i am idling and it does it once in a while in first but the higher the gears i go, the easier it happens and the louder it is. The sound is pretty loud. I can have the radio volume anywhere under 20 and still hear it. Many have said that it is the engine knocking due to bad gas but how long does it take for it to go away if it is due to bad gas? I've already ran it through almost a whole nother tank of gas. My car is an '03 g35c 5at w/68k mi and all I've put into this car is a z-tube, mid chassis brace and rear tie brace. Oh and i've just recently done an oil change w/ mobil1 5w30 synth and mobil1 oil filter if that changes anything. Thanks for any help and suggestions.

 

does the CEL flash?

 

Whats CEL? visually, there is nothing wrong. No check engine light, no nothing. Everything looks fine under the hood.

 

You need to have dealer examine especially since 6 year/70k drive train warranty is still in effect. Get a file going prior to expiration just in case they don't find the problem until after warranty.

 

Thanks, but i would like to pinpoint the problem and see if i can solve it easily before i have to take it into the dealer.

 

Where do you live? There are lots of performance/underground Nissan type shops around.

Rick