Weird Revving Noise

[OutbackAnOutback]

Hello Soobys,

 

A while ago I noticed this noise when I revv'd the engine in my 6-speed 2012 Outback 2.5i.

In order to re-create this noise you have to be moving (forwards or backwards) at least 5mph and have the clutch in. 

With the clutch in, I revv the car up to about 3k and this noise happens. 

Heres a link to a video of me re-creating the noise!
https://www.youtube.com/watch?v=1IevXcFcuJ0

Ive taken it to a couple different places to get the noise checked out, heres what they have said:

Auto shop -  the noise stems from a 5psi backpressure and clogged cat

dealership - valve timing issue

muffler shop - misfire, not the cat

independent soob mechanic - misfire

 

Any help is appreciated, 

Thanks!

Jason

 

[nvu]

sounds like misfire/afterfire.  it's okay if it only does this unloaded and clutch in.  when you press the accelerator past a certain point, the ecu goes into open loop mode.  it fires whatever rich amount of fuel and doesn't rely on any sensor feedback.  the overrich mix doesn't completely burn in the cylinder and could ignite after exhaust port.

this doesn't happen if the engine is loaded down and in gear as it can't freewheel and spit the excess fuel out the exhaust port.  don't worry about it unless it's actually misfiring when the engine is loaded, you'd see the check engine light blinking.

[heartless]

i guess my question is why are your revving it that high with the clutch in anyway?

[OutbackAnOutback]

On 8/24/2020 at 2:39 PM, nvu said:

sounds like misfire/afterfire.  it's okay if it only does this unloaded and clutch in.  when you press the accelerator past a certain point, the ecu goes into open loop mode.  it fires whatever rich amount of fuel and doesn't rely on any sensor feedback.  the overrich mix doesn't completely burn in the cylinder and could ignite after exhaust port.

this doesn't happen if the engine is loaded down and in gear as it can't freewheel and spit the excess fuel out the exhaust port.  don't worry about it unless it's actually misfiring when the engine is loaded, you'd see the check engine light blinking.

Hello! sorry for the late reply  

I took some better videos of the issue, check them out here.

Something I do notice is soot around my tailpipe, but the sound of the noise makes me think that its not a backfire. 

In the video you can hear me revving the engine, around 3k the noise is the worst, and anything above 3k the noise isnt produced. 

So when you hear the engine revving higher at the end, the noise isnt created. 

 

 

Thanks for the help everyone!

[OutbackAnOutback]

On 8/24/2020 at 7:12 PM, heartless said:

i guess my question is why are your revving it that high with the clutch in anyway?

Haha, good question, but the reason I know how to create the sound is because I first started hearing it while downshifting and rev-matching. 

Right as the clutch engages the noise ceases. 

I can also hear it when im in the car and pulling, then suddenly depress the clutch. 

 

Thanks!

JAson 

[nvu]

It never was backfire. It's afterfire, there are youtube videos explaining it.  The noise comes when you let off the gas and it's over rich.  It seems to happen around 3k for your car.  I wouldn't worry about it, it's common on all older cars.  The soot issue sounds like something better to chase since it's a california car.  Basic maintenance, plugs, oil, o2 sensors.  Also 2012 probably falls into the weak piston rings recall, has the car been consuming oil?

Going back to what other shops said, what tests have they done to confirm this.  Backpressure, did they drill a hole before cat and measure? Valve timing, take off timing covers and match timing marks.