Strange exhaust sound: TD42

Engines and Engine Systems
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SJC
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Strange exhaust sound: TD42

Post by SJC » 05 Sep 2017 12:36

Anyone got an idea what might possibly cause this sound on the exhaust. :think:

https://youtu.be/YFdE6t7o-gs

At first I thought it might be a loose bracket on the exhaust, it is not. Sound is coming out of exhaust.
No boxes installed on exhaust, 3" straight pipe.
EGT's are fine. No noticeable loss in engine power.
No white smoke or excessive smoke.
Engine runs smooth, sounds normal.
Not using oil.
Change oil every 5k (delo 400), changed about 500km ago..
Although the mechanic that looked at it recons there is a misfire on the engine. My untrained ear cant hear anything wrong.

He recons a burned exhaust valve can cause it. But from what I googled, a burned exhaust valve would cause a sucking at the exhaust.
>>> " if you hold a piece of cardboard against the exhaust with motor at idle, it will suck on it on the intake stroke if you have a burnt out valve."
Did this and defnately no sucking.
Or is this test not relating to an exhaust valve, but other valves?

So what else? Any ideas? :think: :think: :think:

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Re: Strange exhaust sound: TD42

Post by Dustin » 05 Sep 2017 15:43

Hey Fanus

That exhaust has a good beat to it :lol:
But seriously, I'm not an experts, but I doubt it's a valve because at the start of the video the noise isn't there at idle but only once you rev.
Then the sound isn't a constant beat when it comes back down, where the timing of the valve would be proportionate to the deceleration and a constant beat at idle. It's not in the video.

I would suspect it's an exhaust component touching something or the flex pipe could possibly be tired.
I say this because when I built my exhaust it was my first time doing a job like that so there were a few mistakes I made which resulted in irritating noises. I since fixed them.

I would first run the length of the exhaust and play with it as you go and see what happens to the noise, if you can rule the exhaust out then possibly it is in fact an internal problem, in which case, best call Michael at So-Jo Auto :thumbup:

Let us know what you find.
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Re: Strange exhaust sound: TD42

Post by Kagiso II » 05 Sep 2017 20:19

Excessive carbon in the turbo .. on impeller blades OR one or two of the blades of tiny chip .. The exhozzt amplifies the whistling

Ask JAN Venter [Turbo Works] about that
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Re: Strange exhaust sound: TD42

Post by SJC » 05 Sep 2017 20:22

Dustin wrote:Hey Fanus

That exhaust has a good beat to it :lol:
But seriously, I'm not an experts, but I doubt it's a valve because at the start of the video the noise isn't there at idle but only once you rev.
Then the sound isn't a constant beat when it comes back down, where the timing of the valve would be proportionate to the deceleration and a constant beat at idle. It's not in the video.

I would suspect it's an exhaust component touching something or the flex pipe could possibly be tired.
I say this because when I built my exhaust it was my first time doing a job like that so there were a few mistakes I made which resulted in irritating noises. I since fixed them.

I would first run the length of the exhaust and play with it as you go and see what happens to the noise, if you can rule the exhaust out then possibly it is in fact an internal problem, in which case, best call Michael at So-Jo Auto :thumbup:

Let us know what you find.
But ja, lets hope it is not internal($$$)... If it is, I will be a converted petrol head and curse any diesel for as long as I live... :oldtimer: :mytwocents: :doh: :thumbdown: :biggrin:

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Re: Strange exhaust sound: TD42

Post by SJC » 05 Sep 2017 20:24

Kagiso II wrote:Excessive carbon in the turbo .. on impeller blades OR one or two of the blades of tiny chip .. The exhozzt amplifies the whistling

Ask JAN Venter [Turbo Works] about that
It is not the whistling I am worried about, but the knocking sound...

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Re: Strange exhaust sound: TD42

Post by Michael » 05 Sep 2017 20:40

Fanus, dia heeltemal te moeilik om daai cout te diagnoseer met daai video clip. Dis jammer jy is so ver.

Dis verseker nie n valve nie, hy sal rook as dit n misfire was en hy sal konstant dieselfde ding doen. Kompressie toets sal dit ook bevestig.
Jou turbo is ook fine, dis nie nie probleem nie.

Ek het al n paar precombustion chambers gekry wat los on die head was, maar dit was op pirate heads gewees en nog nooit een op n Nissan head nie. Hulle kan nogals n lawaai maak.

Jy sal moet op die pad ry en n paar goed probeer om te kyk waar die geluid n response het op iets wat jy doen. Hoop dit maak sin, maar dis een manier om nader aan n diagnose te kom sonder om te strip.

Hoor jy die geluid harder by jou exhaust as by jou engine?
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Re: Strange exhaust sound: TD42

Post by SJC » 05 Sep 2017 20:50

Ja, ek hoor die geluid net by die exhaust en nie by die engin nie.

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Re: Strange exhaust sound: TD42

Post by Peter Connan » 06 Sep 2017 05:24

Ek kan net nei dink die is iets in die engine nie. Ek is amper bereid om 'n weddenskap aan te gaan dat die exhaust iewers stamp...

Ek sou 'n kort stukkie tuinslang soos 'n stetoskoop gebruik om te probeer bepaal waar die geluid vandaan kom.
Mag ons ons kenniskry met lekkerkry aanhoukry.

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Re: Strange exhaust sound: TD42

Post by Wilkie » 06 Sep 2017 07:59

Fanus wat gebeur as jy die koppelaar intrap...

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Re: Strange exhaust sound: TD42

Post by ricster » 06 Sep 2017 08:45

This may sound stupid, but bare with me.

The sound is somewhat metallic, even though it isn't a tin metal sound. It almost sounds like a flap of some sorts in flapping in the (exhaust) wind. A little while back I had an issue with my turbo. The little disc shaped flap that controls the revs of the turbine wheel on the exhaust side has a circlip that holds it onto the arm from the ( can't think of the name of it ) valve diaphragm thingy that pushes and pulls the exaust flap open and closed. Now when I had it all open, and manually opened and closed that flap by hand had a very similar sound.

How possible it is that when reving the engine the flap is pushed closed to spool up the turbine, and then when taking your foot off the pedal, the flap is bouncing open and closed in no particular rhythm. Could it be a turbo valve diaphragm thingy failure that isn't giving enough pressure to keep the flap open or closed, so that sound, to me sounds like that flap is flapping open and closed as the exhaust gasses slow down as the revs decrease.
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