97 Outback vibration

[97OutbackTN]

First time post under this name (forgot the password to my last account and had deleted the corresponding email address).

 

I've got a 97 Outback with 123k on it. The car rides very well, but it's developed this problem at highway speeds.

 

Usually above 65mph, there is a loud low-frequency engine vibration. It's hard to describe, but it's as if the fuel line has buildup in it so it's having to try harder to pull fuel through. Once I reach my desired speed (say 75mph) and move to hold it instead of accellerating, the sound gradually subsides, but as soon as I try to speed up, it's immediately back. There's also a bit of power loss as well.

 

I know it's an engine problem because the car rides fine and handling is smooth. It's not the same kind of vibration anyway. It's almost as if someone has left a bass guitar on the same low note with the amp turned up. You can feel it resonating and hear it.

 

My mechanic has said it could be a wide variety of things and it's probably not too serious so not to worry about it. It's just bothersome to me.

 

Any thoughts would be helpful. Thanks!

 

BTW, the car is an automatic and I use premium fuel in it.

[OB99W]

Usually above 65mph, there is a loud low-frequency engine vibration. It's hard to describe, but it's as if the fuel line has buildup in it so it's having to try harder to pull fuel through. Once I reach my desired speed (say 75mph) and move to hold it instead of accellerating, the sound gradually subsides, but as soon as I try to speed up, it's immediately back. There's also a bit of power loss as well.

[...]

BTW, the car is an automatic and I use premium fuel in it.

Well, nobody else has replied so far, and admittedly the description is a bit vague, so I'm going to go out on a limb...

 

There might be a partial exhaust system restriction. That could explain both power loss and "resonating" noise. Acceleration requires higher revs, and consequently more exhaust flow, than constant speed, which may be why things seem normal when cruising. I also noted that you're using premium; does the engine ping on lower grades? If so, while there are several causes for "spark knock", one of them is restricted exhaust. How's gas mileage lately? And although I've never experienced it on my own Outback, a partially clogged air filter can cause funny symptoms on some cars.

 

Of course, I could be totally off-base with all of this, but it's hard to hear, feel, and attach test gear at this distance . Good luck, and let's hear back when this gets resolved.

 

--OB99W

[97OutbackTN]

I know the description is vague...sorry! I wish I could do a better job, it's just a really difficult sound to explain.

 

It's sort of like this: imagine you're inside of a room, and on the other side of the wall in the next room somebody is running a commercial-sized air compressor. If you imagine what this sounds like through a wall, it's a low-frequency hum with a vibration you can feel if you put your hand on the wall. That's what my car sounds and feels like around 70mph.

 

The premium grade I've been using for a few years now because the car started making mild pinging noises, and I haven't had a problem with those since. Fuel economy has been the same. The problem seems to get better as I approach 80 and above.

 

This problem initially showed up after a 90,000 mile service by a Subaru dealer a couple of years ago. It's never been a huge issue, but one that has been bothersome simply because nobody seems to be able to figure the cause out.

[1 Lucky Texan]

Well, nobody else has replied so far, and admittedly the description is a bit vague, so I'm going to go out on a limb...

 

There might be a partial exhaust system restriction. That could explain both power loss and "resonating" noise. Acceleration requires higher revs, and consequently more exhaust flow, than constant speed, which may be why things seem normal when cruising. I also noted that you're using premium; does the engine ping on lower grades? If so, while there are several causes for "spark knock", one of them is restricted exhaust. How's gas mileage lately? And although I've never experienced it on my own Outback, a partially clogged air filter can cause funny symptoms on some cars.

 

Of course, I could be totally off-base with all of this, but it's hard to hear, feel, and attach test gear at this distance . Good luck, and let's hear back when this gets resolved.

 

--OB99W

 

I think you have reasonable explanations given the description(especially the change with throttle use). I'd throw in an ill fitting air filter or the box not being clipped in properly over the filter.

 

I wonder if the use of the word 'vibration' is indicating strictly sound or also a feeling? Also, is the sound from the front, under the hood? At 75 you're likely doing over 3100 rpm, does 3100 rpm make the same sound at lower speeds?(in a lower gear of course). seems a clogged cat converter is a good guess. Any 'history' on the vehucle we should know about? like a rich-running condition or recent repair work?

[nipper]

im thinking its a partially clogged catalytic converter. Here is a test if it is. Next time the problem occurs, note what engine rpm it is happening at. Next shifting the car manually, in D3 see if it happens at the same engine rpm, and at d2. It should happen but at a lesser extent due to the rpm/hp curve ... just an idea. A cloged cat doesnt always throw a code, but it will get worse with time. Other possabilities are a collapsed exhaust system, or as stated before a blocked air box.

 

 

nipper

[OB99W]

...The problem seems to get better as I approach 80 and above.

 

This problem initially showed up after a 90,000 mile service by a Subaru dealer a couple of years ago. It's never been a huge issue, but one that has been bothersome simply because nobody seems to be able to figure the cause out.

If the situation improves at higher speeds, then my theory concerning exhaust restriction becomes somewhat less likely. As suggested, determining if the noise seems related to engine speed or road speed would be useful.

 

Since you know that the problem became evident after a particular service, is there any possibility that you could tell us what was done at the time? I do realize that you might not still have the paperwork, or that something happened that the dealer didn't document, but some more clues might help.

 

--OB99W

[97OutbackTN]

I feel like I'm working with a bunch of doctors who are trying to understand a problem I'm having and offer possible causes.

 

I've replaced the air filter before and it's had no effect. My current air filter needs to be replaced though so I'll try that and check the box while I'm at it.

 

I'll give the catalytic converter test a shot as well. I haven't really noticed the problem during regular accelleration, but of course I'm only above 3000rpm for a few seconds.

 

The noise itself, along with the vibration, seems to be coming from the front of the car...either engine area or underneath the front row of seating.

 

As far as the car's history, it seems to be fairly normal. There is a knocking noise that occurs when the car is idling, sounds sort of like a piston slap (I think), but my mechanic said it's common on these cars as they get older and is not a problem.

[97OutbackTN]

If the situation improves at higher speeds, then my theory concerning exhaust restriction becomes somewhat less likely. As suggested, determining if the noise seems related to engine speed or road speed would be useful.

 

Since you know that the problem became evident after a particular service, is there any possibility that you could tell us what was done at the time? I do realize that you might not still have the paperwork, or that something happened that the dealer didn't document, but some more clues might help.

 

--OB99W

 

In looking at the service record, I can find very little that looks like it might be related. The ones that pop up are

 

- replace fuel filter

- replace air filter

- replace pcv valve

- drain and refill coolant

- install air control valve (this might be the same as PVC)

 

I do know that I bought the car with 79k on it, so I don't have a record of service prior to this. I have no idea what service was done up to that point.

[nipper]

air control valve is not a pcv. any buzzy noise you hear may be a heatsheild.

 

ill pick this up tomorrow as the pain meds are kicking in ... goodnight all

 

 

nipper

[1 Lucky Texan]

In looking at the service record, I can find very little that looks like it might be related. The ones that pop up are

 

- replace fuel filter

- replace air filter

- replace pcv valve

- drain and refill coolant

- install air control valve (this might be the same as PVC)

 

I do know that I bought the car with 79k on it, so I don't have a record of service prior to this. I have no idea what service was done up to that point.

 

If the problem presented itself soon after the above service - definitely look for a poorly reattached hose or the intake filter box dealie not tabbed into its slots.

 

I think I'll go look for some pain meds, thanx for the idea nipper!

[OB99W]

- replace air filter

As has been mentioned, the air filter housing may not have been latched correctly, etc., when the filter was changed. Here's something to look at related to that:

http://groups.google.com/group/alt.autos.subaru/browse_thread/thread/49c275da984e5701/920875b27a0693f4%23920875b27a0693f4?sa=X&oi=groupsr&start=0&num=3

 

--OB99W

[idosubaru]

your sure it's coming from the engine, front of the car?

 

does it do anything while sitting in neutral but reving the motor up to 3,100 rpms'? get a helper and try it with the hood open and listen/look around. or just open the throttle by hand if you know how to do that, then you can do it yourself.

[97OutbackTN]

I'm going to check (and replace) the air filter...now how do I get that housing off? I unlatched the clips, but couldn't get the thing to pull off.

[nipper]

I think I'll go look for some pain meds, thanx for the idea nipper!

 

I'm slightly disturbed that they fit in a pez dispencer. Did you try the rpm test yet?

 

nipper

[97OutbackTN]

Well, I replaced the filter and checked the cover. It seems to have improved a bit, but it's still there. What it sounds like is it occurs when the RPMs are over 3000 in 4th gear and the engine is working hard (like going up an incline).

 

I know for sure it doesn't make this noise and feel when I'm simply revving the engine in Neutral. It also doesn't do it when I'm accellerating. I have not done the catalytic converter test as listed above, but will when I get a chance. However, I'm willing to bet it comes back negative just because of the fact it doesn't make the sound during accelleration.