Hey guys,

I have this weird slapping kind of knock noise when my car is idling. It is especially noticable at start up. It sounds like it is coming from the driver's side part of the engine somewhere. I thought, and still do think, it might be an exhaust leak at the y-pipe to manifold flange because I had my exhaust guy try putting an aftermarket y-pipe on to no avail, so he put back on the stocker. The noise is like a slap, slap, slap, or puff, puff, puff...my dad said it sounded like a slapping piston, but its not extremely loud, only at idle is it really noticable. I know its not the injector or valve tick, its totally different. Help!

 

when you rev it up does the noise go away or get louder and advance with the engines revs ??

its possible especially since you had your exhaust worked on already that its leaking now because he took it apart

 

sounds like detonation to me check your timing

 

detonation is a pinging.

Is "ticking" a good description of this noise? if so, then yes an exhaust leak is a definite possibity.

 

Its not a "ticking" so to say, its more of a puff, puff, puff, slap, slap, slap type of noise. My timing is fine, I set it to 0* spec and then advanced it to 2* where it was running nicely. Yes, I disconnected the ESC to set base timing. I'm hoping its exhaust, but what else do you think?

 

it sounds like exhaust, but at the same time, you say it is only noticeable at idle...but that could also be because you have loud exhaust...i would say exhaust...try tightening the connection...

Josh

 

pinging describe the sound in detail

 

If it's exhaust it will be in tune with RPM and it will GET LOUDER THE MORE LOAD YOU PUT ON THE ENGINE. If it's constant in volume or goes away when you get above idle speeds it's not an exhaust leak.

A valve tap will be very similar but it'll be constant volume regardless of engine load.

 

My car spun the balancer which sounded like that when it hits the timing chain cover...

 

if you still have stock manifolds, check to see the AIR tubes are all screwed in nice and snugly... one of mine spun itself out and made a nasty leak

 

maybe you collapsed a piston. sounds alot like piston slap. What type of pistons are you running? do you know what your piston to wall clearances?

IF you want to hear some good piston slap fir up any gen III small block chevy, whether its the 5.3, 5.7, or the 6.0. they all slap around quite a bit when they're cold. Sounds like some good old fashioned MIN-MAX