STRANGE ENGINE KNOCK... What the hell is this???

[djerok]

I am the proud new owner of a 1997 Q45. The car has a decent amount of mileage (123K) but it looks and runs mint. I sunk a few bucks into the car when my check engine light came on. I replaced o2 sensors and got some exhaust work done (fixed leak). I noticed that when the car is in drive and I have my foot on the break, occassionally there is a strong knock that comes from underneath the hood. I happens once, maybe twice, and then it stops. It does not happen when the engine is moving over 500rpm. I mentioned this to infiniti when i got the car worked on and they checked it out and said it was fine. the car still runs mint even right after the knock. This is driving me crazy... anyone had any similar problems? I've changed all the fluids when i purchased the car.

[Q45tech]

ABS cycle test when you first crank and back up in reverse?

[texasoil]

potential cross fire caused detonation? Overheating ? too lean in one cylinder?

[VJ1]

If you feel a pulse on the brake pedal when you hear the knock, it will be the ABS self test, which is perfectly normal.

[djerok]

I also thought that it may be the ABS, however the knock also occurs occasionally when the car is in park. The knock is at times very powerful and can be felt throughout the front of the car. I feel a pulse on the brake when this happens, but i think the noise is way too loud to be just the brakes.. It really fells like the motor is knocking, but the car does not lose any power and still drives like a dream at all times.... service engine light isnt even on.... i'm puzzled... i wouldnt care but that knock bugs the hell outta me.... anyone experience anything similar?

[xerexabante]

try to get your timing checked out it might be too advanced, and that it maybe your knock sensor. it could be a miss fire is what i really think you have. maybe one of your coils are not functioning correctly and or a dirty injector. try to get some injector cleaner that you trust.

if you feel that it is an engine knock try to use a thicker oil, and or try some oil addetive and see if it will still knock. if symptoms presist you might a knocking cranck shaft bearing. best of luck to you sir.