Wife noticed noise from engine at idle - Nissan Murano Forum
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#1 Old 06-06-2010, 10:22 PM
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Wife noticed noise from engine at idle

Wife complained of noise coming from engine when idling.
So went outside and had a listen. Indeed, when in idle, the engine sounds very burly, like a more open exhaust can was put on (mine is stock and exhaust seems not to have any holes).
When idling the sound can be heard from the far side (down) of the engine (close to cabin firewall), and sounds like a growly, sports car like noise. When you press on the gas it seems to dissipate somewhat, but I am sure it is partly due to the rpm noise.

Can anyone point me to the possible causes? I am worried this may get really worse somehow.
Really appreciate it.
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#2 Old 06-06-2010, 11:07 PM
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Bottom of the engine, towards the firewall - sure seems like an exhaust pipe leak to me. Your mechanic can pinpoint small exhaust gas leaks by using a probe that can detect hydrocarbons - this tool can detect leaks even if they are not obvious.

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#3 Old 06-07-2010, 12:55 AM
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not so sure it is exhaust pipe. It is in real good shape still and no corrosion/damage exists. Seems like something else maybe. I started to think the fuel injector damper??? Again, looking for any possibilities. Thanks. will recheck.


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Originally Posted by Eric L. View Post
Bottom of the engine, towards the firewall - sure seems like an exhaust pipe leak to me. Your mechanic can pinpoint small exhaust gas leaks by using a probe that can detect hydrocarbons - this tool can detect leaks even if they are not obvious.
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#4 Old 06-07-2010, 11:25 AM
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Quote:
Originally Posted by ciaka View Post
I started to think the fuel injector damper??? Again, looking for any possibilities. Thanks. will recheck.
According to the Nissan Service Manual you can easily determine if the source of the noise is one of the fuel dampeners by grasping the fuel rail and feeling if the vibration coincides with the sound you are hearing. You will need to remove the cosmetic engine cover to access the dampeners.

-njjoe
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#5 Old 06-07-2010, 12:08 PM
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Thanks again Njjoe.
I will look again today. The noise is hard to pinpoint. Harder to hear from the cabin, and definitely sounds like a throaty deep open exhaust sound. But i did put it up yesterday thinking that the exhaust header pipe is bad. Looked it over and do not see any structural compromise at all. The pipes are in great shape (here in TX no need for salt, etc).

How is this replacement done (fuel dampers). Have a few questions:

- what do fuel dampers do?
- will I need to replace both or how do I tell which one to replace if only one is bad?
- Which fuel rail (dumb question - what is a fuel rail) do I grab to feel the vibration - the one connected to the dampers I assume? Is it correct to assume that the damper which is still good wont have the vibration?
- if the noise is a result of the fuel damper going bad, what generates the sound? In other words, how is that throaty sound created when the damper goes bad? I do not feel exhaust air escaping in the area. Wanted to understand this more.

Thanks again.




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Originally Posted by njjoe View Post
According to the Nissan Service Manual you can easily determine if the source of the noise is one of the fuel dampeners by grasping the fuel rail and feeling if the vibration coincides with the sound you are hearing. You will need to remove the cosmetic engine cover to access the dampeners.

-njjoe
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#6 Old 06-07-2010, 01:24 PM
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Quote:
Originally Posted by ciaka View Post
How is this replacement done (fuel dampers). Have a few questions:

- what do fuel dampers do?
- will I need to replace both or how do I tell which one to replace if only one is bad?
- Which fuel rail (dumb question - what is a fuel rail) do I grab to feel the vibration - the one connected to the dampers I assume? Is it correct to assume that the damper which is still good wont have the vibration?
- if the noise is a result of the fuel damper going bad, what generates the sound? In other words, how is that throaty sound created when the damper goes bad? I do not feel exhaust air escaping in the area. Wanted to understand this more.

Thanks again.
There are no dumb questions here. (Okay,maybe there have been a few from time to time. )

1) Fuel dampers smooth out the pressure pulses within the fuel system. In order for the fuel management system to operate effectively the pressure within the fuel rails needs to be constant. The fuel dampers will "absorb" the high pressure pulses and make-up lost pressure as needed. These pressure variations all occur within fractions of a second.

2) The fuel dampers work independent of each other. So if one fails the other may still be okay. When you touch each one you can tell which is one is bad by feeling the vibration. The one that vibrates in concert with the sound you hear is the one that is bad.

3) The fuel rails are the small tubes that connect to each injector. They are listed as item#4 in the diagram I attached in my previous post. The fuel dampers are the two items within the red squares in the diagram.

4) A bad damper usually results in a chattering diesel-like sound, not a throaty sound. If what you hear is a throaty sound then it probably is not the dampers.

5) The fuel damper is nothing more than a small vessel that is separated into two sections by a diaphragm, one half is sealed and the other is connected to the fuel system. Pressure pulses cause the diagram to move.

-njjoe

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#7 Old 06-14-2010, 01:48 AM
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OK.

So I have been monitoring this noise and this is what I found (to clarify/improve on above info):

- the noise is a louder/deeper sounding car...like a truck running (sort of what people say a diesel truck type of a sound).
- the noise seemed to be located on the back side (close to passenger cabin firewall) area, although it is very difficult to pinpoint. Can hear it better from the side of a car.
- the noise is not a separate noise in addition to the regular engine sound noise. The noise is the engine running noise, except that it has changed into this deeper, truck like noise
- I pulled off the plastic cover from the engine and placed my hand on the fuel rail (at least I think I did). As I had the engine accelerate, there was 'clicking' type of vibration felt from the fuel line, and it was synchronized to the engine running, but it did not seem to me as though it was the cause of the deep engine sound from the car (still wondering how a faulty fuel damper can cause a car to sound like this). It was a clicking/vibration like noise felt across the fuel rail, so if someone can jump in to explain how this could lead to the engine sounding so burly, it will be great.

So if someone can still help me try to nail down exactly what I am faced with, I will really appreciate it.
Is there a good way (for me with my regular tools) to tell if it is the fuel damper or the intake manifold? Someone suggested it could be intake manifold leak but I want to see what I can do to test for each and nail down the cause and replace once.
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#8 Old 06-14-2010, 02:06 AM
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Intake manifold leak? I don't think so because you would then have a rough running engine. Exh manifold leak (via a crack) is possible. I am siding with the fuel damper problem because it is common.

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#9 Old 06-14-2010, 11:57 AM
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An easy way to determine if it's an intake leak is to take a can of carb or electrical contact cleaner and spray the seals on the upper and lower intake manifold and the throttle body. If you spray an area and notice the RPM change (increase I think...haven't done this in a while) then you definitely have a leak. Do this with the cosmetic cover off though; you won't be able to reach the seals otherwise.

The picture that Njjoe attached is a good reference. I'm just not sure if those dampeners are located on the driver or passenger side of the engine. The picture gives no reference.

Maybe it's time to go over the engine with a stethoscope.

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#10 Old 06-14-2010, 03:15 PM
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a friend of mine took a couple minutes to listen in on the sound and says it sounds like exhaust manifold leak.
I gave him background info on the fuel dampers and he says that he does not hear noise coming from the dampers, but from the behind engine area, close to cabin. I hear sound coming from same area.

So my next question is, is the sound supposed to be coming from the dampers if they are bad, or is the breakage of a fuel damper manifesting in noisy engine running that closely resembles exhaust manifold leak?

I again felt the fuel rails and touched the dampers (which are located on the right side of each fuel rail - when facing the front of the car), and they seemed to vibrate but in a manner that seemed to indicate ticking like feeling (as if the dampers are oscillating???). I did not feel any very large vibration that I would associate with broken damper, so if someone can jump in and try to tell me what a broken damper should feel like, or what a regular damper should feel like, it will give me a better gauge for what I should be feeling for. Really appreciate your awesome help murano forum folks.
Can someone also tell me if this is a broken damper, would the additional sound be coming from the damper, or would the emitting sound be still manifesting as a manifold lead (exhaust), and what the reason behind the sound be (what about the broken damper could cause the engine to sound like this). Thanks again.
In the mean time, i will be trying to see if I can exclude the exhaust manifold probability (will also welcome ideas to exclude it, aside from having a exhaust probe which I do not have - a good way to say yea-nay about the exhaust manifold).
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#11 Old 06-14-2010, 05:25 PM
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I just read something interesting on the internet in regards to a surefire way to find an exhaust leak. You can do one of two things:

1) Pour something into your engine that will create white smoke. SeaFoam, Oil, etc will do this. Then plug your exhaust for a moment and see where the white smoke comes from in the engine compartment.
2) With your warm engine off, inject some smoke into your tail pipes and take note of where the leaks are. The smoke has to be under pressure of course so the smoke will come out of the areas.

I like the second option better than the first but most people don't have a way to inject pressured smoke into their tail pipes.

Either way, it was just a thought. Good luck!

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#12 Old 06-14-2010, 06:06 PM
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most people don't have a way to inject pressured smoke into their tail pipes.
Unless they are blowing off smoke.....

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#13 Old 06-16-2010, 10:18 PM
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crawled under and the sound seems to be coming from the rear exhaust manifold area.
Also noticed that there is a nut missing on one of the 4 bolts holding the catalytic to the manifold. Could this be the cause? Anyone have a bolt rattle off like that? I gotta now find out what kind of bolt it is and try to put one on there to tighten.
The dampers seem to have vibration but I have no idea what type of vibration would constitute one being defective. The vibration is not big, appropriate for a device that has a membrane inside which oscillates. Other than that, it is all I noticed. Still looking.


Anyone done their exhaust manifold on the MO? Hard? Easy? Tips? Etc.
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#14 Old 06-16-2010, 10:48 PM
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The rear exhaust manifold is a bear to get to from what I understand. From down below you need to remove almost everything. From up above I think it's pretty much everything on the top.

If I were you, I would get the service manual and follow the instructions. But first you should replace the gasket on the exhaust flange and get another nut.

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#15 Old 07-05-2010, 01:01 AM
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Well, to make a long story short, it was a cracked exhaust manifold (the rear one, closest to passenger cabin).
Knowing how difficult it will be DIY, I took it to a place which charged me just under $400 to have it done, including part cost.
Knew the service manager so I got to have the part at their cost and had a few other discounts to make it easier on the pocketbook.
Now, the MO purrs back the same way it did as before.

I also noticed that the mileage was improved substantially relative to the time when the manifold was cracked. Would that be true or am I just seeing things? I continuously got mileage at about 15-17mpg when in 'cracked' mode, and now seeing 18-21 when in 'uncracked' mode.

Thanks to all who provided input.
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