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Intermittent hissing and loss of power

Tiny
TYLER KIRK HOOVER
  • MEMBER
  • 2003 SUBARU OUTBACK
  • 4 CYL
  • AUTOMATIC
  • 75,000 MILES
I have a Bluetooth OBII tool that I used to get some of these readings.

I am able to drive the car along and it seems to operate normally. Then all of a sudden there is a hissing noise. When inside the car it sounds to be coming from somewhere around the transmission. When outside the vehicle with the hood up it sounds louder toward the back of the engine and louder under the car. The sound also gets louder when acceleration. There is also a major loss in engine power during this.

I am not 100% sure this has to do with the problem Using the OBDII tool I noticed twice so far that it seems to happen with the engine reaches about 190° Both times I waited for the engine to cool down and bit and it drive fine again. I plan on testing this a few more times.

Do you have any suggestions for what I should be looking at? I haven't found any problems with the vacuum hoses yet but that was my first thought because of the hissing sounds.
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Thursday, February 6th, 2020 AT 8:47 PM

16 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,300 POSTS
Hi,

Based on your description, it sounds like you have a plugged catalytic converter. Take a look through these two links. The first one explains the symptoms of a bad converter and the second explains how to test one.

I think the sound you hear is air being forced through a restricted exhaust system. That will cause a sound as described and a major power loss.

https://www.2carpros.com/articles/bad-catalytic-converter-symptoms

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

Let me know if the symptoms mirror what you experience. I can explain how to replace one if that is determined to be the problem.

Take care,
Joe
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Thursday, February 6th, 2020 AT 9:13 PM
Tiny
TYLER KIRK HOOVER
  • MEMBER
  • 18 POSTS
I plan on doing the temperature test as soon as possible. I have a question about the vacuum test though. Using an app to monitor the OBD tool there is a vacuum monitor. I've checked that the same way it describes in the test both while experiencing the sound and loss of power but the readings where normal. Would you trust vacuum readings from the OBD? Also what I read seems to indicate that there should be a check engine light. I haven't had a check engine light on at any point.
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Thursday, February 6th, 2020 AT 9:51 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,300 POSTS
Hi,

One would think you would have found a P0420, but it doesn't always happen. As far as the scanner and vacuum, Ugh! I don't know how dependable that would be.

Pull an o2 sensor before the converter to see if it makes a difference. You will get a code for that, but you will know why. If it runs a bit better (because you are only providing a small exhaust opening via the sensor) then most likely it is the converter.

Let me know what you find.

Joe
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Friday, February 7th, 2020 AT 11:13 AM
Tiny
TYLER KIRK HOOVER
  • MEMBER
  • 18 POSTS
I pulled the sensor and so far it has actually been running a whole lot better. Before I could hardly get the car to a safe speed to drive on the road and now I can drive it just fine. I've driven it like this for about two days (Since the problem was intermittent) and it's driven fine the whole time. I am going to try and look in the converter with a camera tool just to make sure.
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Tuesday, February 11th, 2020 AT 6:37 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Tyler, if it helped, the converter is the issue. Now there are two converters (front and rear). I like the idea of the camera tool to confirm which one is the issue. Also, there are two sensors. One for the front and the other is for the back. Based on which sensor you removed can also answer that question.

Also, often times the converter will come loose internally and intermittently cause a blockage. Usually you can hear it rattle. You can tap on the system with a rubber mallet to see if one sounds loose.

I attached a pic. Let me know what sensor was removed or let me know what you find with the camera.

Take care,
Joe
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Tuesday, February 11th, 2020 AT 7:43 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,300 POSTS
Tyler, if it helped, the converter is the issue. Now there are two converters (front and rear). I like the idea of the camera tool to confirm which one is the issue. Also, there are two sensors. One for the front and the other is for the back. Based on which sensor you removed can also answer that question.

I attached a pic. Let me know what sensor was removed or let me know what you find with the camera.

Take care,
Joe
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Tuesday, February 11th, 2020 AT 7:43 PM
Tiny
TYLER KIRK HOOVER
  • MEMBER
  • 18 POSTS
I took off the sensor before the first converter (number 1 in the diagram). I put the camera in the sensor port (it only let me attach 1 picture) What I can see there seems very clean. I haven't been able to get the number 2 sensor off yet to try and check the second converter. At this point, that doesn't really matter correct? The diagnosis is still a converter is bad. I tried to go in from the tailpipe with the camera but I couldn't get around in the muffler so that didn't happen.

From what I have found parts wise and my inability to be able to weld it would be easier and most cost effective to replace both of them. So either way, a converter is bad so I should replace this?
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Thursday, February 13th, 2020 AT 11:33 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

That does look good. If it ran good when you removed the oxygen sensor, something is causing too much back pressure in the exhaust. Most commonly, it is a catalytic converter. Please understand, I can't be 100% sure without seeing it. However, that is my first suspect.

Now, the second converter you mentioned should be able to be replaced with a universal type. You should be able to cut the old one out and clamp a new (universal) one in.

Let me know.

Joe
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Friday, February 14th, 2020 AT 2:14 PM
Tiny
TYLER KIRK HOOVER
  • MEMBER
  • 18 POSTS
Thank you very much for all of the help I learned a lot from it. I was finally able to get take the pipe with the converters off of the car and got a good look inside the second converter (picture attached). This is definitely bad.
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Wednesday, February 19th, 2020 AT 1:44 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,300 POSTS
Glad to help. Yes, that doesn't look too good. Chances are the insides were moving around plugging the system. Regardless, I'm glad you got to the bottom of it.

If you have a chance, let me know if this takes care of the low power issues you were experiencing. I'm interested in knowing and certain that others will benefit from your repairs.

Take care,
Joe
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Wednesday, February 19th, 2020 AT 8:00 PM
Tiny
TYLER KIRK HOOVER
  • MEMBER
  • 18 POSTS
I will definitely post again with the results once I have put on the new part and put on some miles to make sure it's all taken care of.
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Wednesday, February 19th, 2020 AT 8:13 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Sounds great. If you need any directions, let me know.

Joe
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Wednesday, February 19th, 2020 AT 8:37 PM
Tiny
TYLER KIRK HOOVER
  • MEMBER
  • 18 POSTS
I am sorry that I have not gotten back to this thread; I'll explain in a moment. As far as I could tell all the issues were solved the car was running great. Sadly it is no longer running at all. In early March Someone speeding down my street running late for work slammed into my car along with three others and my car was totaled. So that's the end of that. It has been a pain for about three months and now it's hopefully about to be over. Thank you so much for your help I will be passing this along to everyone I know and using the service in the future.
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Thursday, April 30th, 2020 AT 6:40 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,300 POSTS
Wow! That sounds like the type of luck I would have. I'm just glad you weren't in it. It's only a car. They make them every day. LOL

Listen, if you ever have questions in the future, let us know.

Take care,
Joe
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Thursday, April 30th, 2020 AT 9:15 PM
Tiny
TYLER KIRK HOOVER
  • MEMBER
  • 18 POSTS
Thank you very much I will be back for sure. Because I bought it at auction and did all this work myself I might actually be making money off this so that makes it easier to be optimistic about it.
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Thursday, April 30th, 2020 AT 9:20 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,300 POSTS
That certainly would make it easier to deal with. Regardless, take good care of your self and you are very welcome.

Take care,
Joe
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Friday, May 1st, 2020 AT 8:17 AM

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