Loud knocking at 3000 rpm... Help!
Nordschleife Master
Joined: Oct 2007
Posts: 5,471
Likes: 209
From: Tacoma, WA
Try to put the camera under the rear tire, or in the engine bay. Then hold the idle where it makes the most noise.
From your video, it sounds normal to me. To bad you are so far away from me.
From your video, it sounds normal to me. To bad you are so far away from me.
Burning Brakes
Joined: Oct 2009
Posts: 817
Likes: 8
From: Near St Louis
Sounds like a spark knock as you add throttle just at that one point then clears. Does it have the stock chip? did you check dist belt? how are the plugs? cheap gas? etc...
Or it could just be a vibration.
Doesn't sound like a rod or lifter so that's good news.
Or it could just be a vibration.
Doesn't sound like a rod or lifter so that's good news.
Thread Starter
Racer
Joined: Mar 2007
Posts: 253
Likes: 1
From: Arlington,WA
I thought spark knock as well. I did the test with the spray bottle in the dark and it had no affect nor did I see any sparks. Can spark knock happen in a range of rpms such as 3000-3500 and then go away in higher rpms?
Racer
Joined: Jan 2008
Posts: 270
Likes: 4
From: SoCal
I recently have been hearing a knocking sound from my engine. The noise only occurs when I hit right around 3000-35000 rpm. I only hear the sound between those rpm's. It does not sound good, so I have only driven it twice since first hearing it. I dont have a P-car mech nearby or I would have taken it to a shop, but I am reluctant to drive a great distance. Any Ideas or thought would be greatly appreciated. TIA. By the way, its a 1995 993 with 120k on the clock.
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Rennlist Member
Rennlist Member
Joined: Jul 2004
Posts: 10,607
Likes: 2,051
From: Dallas, TX
OK, I listend to the video and did not here a knock. Unplug your primary distributor and verify that the car runs on the secondary only to rule out out of time ignitions caused by a broken distributor belt. Also a knock as I know them sounds a lot like a noisy valve but lower and in some cases deeper in frequency. I here some noises that sound higher frequency like engine or exhaust sheet metal or rattling. One last thought. Does your car rattle for a few moments at start-up and then quiet down. If so you may be hearing a valve adjuster.
Andy
Andy
Burning Brakes
Joined: Dec 2003
Posts: 1,036
Likes: 12
From: Chicago, Il
All ears are different. Mine are old. So, I'll take a SWAG on the noise. First off, it is not what I would characterize as a "knock". It's a resonance of some part in the car.
Second, I do NOT think it is an engine or transmission internal part. If you listen carefully you should note that the engine changes in RPM and the pitch of the "knock" do not track perfectly one with the other. Change in mystery noise loudness lags changes in engine speed. That's a good sign of resonance.
Best SWAG: You have a metal bracket or fitting somewhere on the car that is loose and is being resonated by engine produced frequencies. Personally, I would not be concerned about driving it to a mechanic.
To find the noise, you'll probably have to look into the engine compartment or from under the car while having someone find the "sweet spot" in engine speed that maximizes the mystery sound. At that point, start touching brackets and fittings of the engine or accessories that might be suspect. When you find the part that gets quiet as soon as you put your hand on it.........you've solved the mystery.
Chances are that either a 10mm or 13mm wrench will parish your mystery!
Let the forum know what you find.
EDIT: Just picked up 996'er comment about the date. Duh! Guess the OP got the item fixed, right? Wonder if it took the 10 or 13 mm open end to sort out?
Second, I do NOT think it is an engine or transmission internal part. If you listen carefully you should note that the engine changes in RPM and the pitch of the "knock" do not track perfectly one with the other. Change in mystery noise loudness lags changes in engine speed. That's a good sign of resonance.
Best SWAG: You have a metal bracket or fitting somewhere on the car that is loose and is being resonated by engine produced frequencies. Personally, I would not be concerned about driving it to a mechanic.
To find the noise, you'll probably have to look into the engine compartment or from under the car while having someone find the "sweet spot" in engine speed that maximizes the mystery sound. At that point, start touching brackets and fittings of the engine or accessories that might be suspect. When you find the part that gets quiet as soon as you put your hand on it.........you've solved the mystery.
Chances are that either a 10mm or 13mm wrench will parish your mystery!
Let the forum know what you find.
EDIT: Just picked up 996'er comment about the date. Duh! Guess the OP got the item fixed, right? Wonder if it took the 10 or 13 mm open end to sort out?
Rennlist Member
Joined: Jul 2009
Posts: 7,234
Likes: 10
From: Costa Mesa, CA
I think this rules out a bearing or other problem as it is not load-related. Likely a loose bracket or muffler baffle. WOuld be nice to have gotten a resolution post.
