swmic

bad lifter? Or would that be obvious at idle?

Stealth 993

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.

rsr91128

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.

Redblurr

I will try to take a closer video. The Knock happens both on acceleration and deceleration. Thanks for all the views.

Redblurr

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?

techman1

Distributor - Broken belt and preignition?

george996

what was the resolution to the problem?

nine9six

Difficult to tell...The thread is almost 4 years old. I guess you could PM the OP and ask if you are curious.

pp000830

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

earossi

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?

vincer77

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.