Tapping sound from the engine?

[D.K.]

Impreza 93, FWD, 72Kmi has developed strange sound couple
weeks ago: Rather low-pitched, "tapping" or "knockng" that sounds
like it is synchronized with the engine (as if a small hammer on a
wood, fairly frequently and at some distance). The sound comes from
under the hood (seems to be closer to the passenger side). It is heard
only when accelerating (the harder, the louder the sound), and disappears
very quickly as soon as I take foot off the gas pedal.

Oil level is OK, during the last weeks that the sound appeared
milage remained the same, oil is not burned, other than this extremely
annoying sound, the car feels normal.

Any ideas what this might be? Someone told me I might be killing the
engine by driving it without fixing the problem. How likely is that?
Unfortunately, I will not be able to get to the dealer this week, and
maybe even next one...

Thanks a lot for any hints!

DK

 

[Bill Putney]

I have exactly what you describe happening with my 2000 OBLW. The sound I
have is somewhere between a tapping and a putting sound. The harder you
apply the throttle the louder it gets - seems noisier in cold weather too. I
haven't gotten to the dealer yet and I am just out of warranty (2 months
now) so I'm not looking forward to it.

The car seems to run fine aside from the noise so I have a feeling it may
just be a crack or hole in the exhaust near the engine - nothing I've been
able to locate or verify unfortunately. I'm very interested if anyone else
has had the same experience and knows what it might be before I put my
subies life (and my wallet) in the hands of the dealer's mechanics.

Regards,

Gerard...

Sounds like piston slap. Do a Google search on that on this ng.
There's been much discussion of that.

As far as the OP's '93, I'm not too sure. Piston slap appears to be
more of a problem with some of the later engines.

Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")

 

[Edward Hayes]

If it is exhaust related it may fall under the clean-air act and is
warranted for 80,000 miles?

 

[Ed Rachner]

Check the inner boot of the axle on that side of the engine to see if it is
torn. A bad DOJ on the axle generally starts as a vibration that increases
with throttle and speed and suddenly disappears when you let off on the gas.

 

[Tony K]

I had the same problem with a 2001 Outback. I thought that it was a bad
lifter. Since the car was still under warranty I brought it back to the
dealer. It turned out to be the idler pulley for the serpentine belt (bad
bearing).

 

[Douglas Barr]

I've had a similar noise on my 02 Legacy. If the sound is worst when the
engine is cold and tends to disappear when warm it could be the timing belt
tensioner. That's what mine was. Replaced under warranty (UK warranty is 3
years/60K miles).

If this is what the problem is, it doesn't seem to do any harm to run the
car with the noise present.

Regards

Doug

 

[SpongeBob]

Had a similar sound w/ 99 Outback. Thought it had something to do with the
clutch/transmission. Took it to the dealer who discovered it was the heat
shield on the catalytic converter. The shields are not stainless and tend to
rust. They welded it back on since it was still somewhat solid and the sound
was gone. The dealer said it is quite common and they often remove them
completely.

 

[D.K.]

As far as the OP's '93, I'm not too sure. Piston slap appears to be
more of a problem with some of the later engines.

I don't know how helpful this might be but one additional thing:
the "tapping" sound only happens when the car is in gears.
There is no such sound when I rev up the engine while in
neutral. (Does that means it's not engine-related?)

DK

 

[Bill Putney]

I don't know how helpful this might be but one additional thing:
the "tapping" sound only happens when the car is in gears.
There is no such sound when I rev up the engine while in
neutral. (Does that means it's not engine-related?)

DK

Yeah - that sounds more like a CV joint problem that Ed Rachner
mentioned.

Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")

 

[D.K.]

Yeah - that sounds more like a CV joint problem that Ed Rachner
mentioned.

Thank you. I have replied to him in this thread asking couple
more questions. Mind looking at it? Another thing I have noticed
yesterday: that sound was gone for a while after the car was
parked for many hours under sun during a hot day (>80F).
In the evening, when things got cooler, it resumed again.
Does this make any sense with regard to CV joint idea?

DK

 

[Bill Putney]

Thank you. I have replied to him in this thread asking couple
more questions. Mind looking at it? Another thing I have noticed
yesterday: that sound was gone for a while after the car was
parked for many hours under sun during a hot day (>80F).
In the evening, when things got cooler, it resumed again.
Does this make any sense with regard to CV joint idea?

DK

CV (constant velocity) joint - its part of the drive axle - there's a
left and a right - each called a half shaft. Replace the half shaft.
Since you asked what a CV jopint is, I assume you don't do much of your
own work - if that's the case, best take it to a shop. Haven't done one
a few years, but I believe price (parts and labor) would run $125-$200.
Careful - there are some junk aftermarket half shafts out there. You'd
be wise to insist on one from NAPA - they seem to pay attention to
supplier quality than some of the other chains.

I wouldn't expect temperature to affect it much - possibly grease got
warm and filmed over the moving parts a little so it was quiet for a
while, but I wouldn't focus on that too much.

Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")

 

[D.K.]

CV (constant velocity) joint - its part of the drive axle - there's a
left and a right - each called a half shaft. Replace the half shaft.
Since you asked what a CV jopint is,

I know (on paper) what CV joint is, but Ed mentioned DOJ which
I've never heard of. After some search I conclude that the Double
Offset Joint is one of the possible varieties of CV joints. Correct?

I assume you don't do much of your
own work - if that's the case, best take it to a shop. Haven't done one
a few years, but I believe price (parts and labor) would run $125-$200.
Careful - there are some junk aftermarket half shafts out there. You'd
be wise to insist on one from NAPA - they seem to pay attention to
supplier quality than some of the other chains.

Thank a lot! I did look under the car - the boot there is clearly torn
badly, which I now understand probably resulted in some damage/wear
off in the joint.

DK

 

[Gerard]

Nice to see you've got your noise sorted. My boots look fine so I'll have to
look further afield. The noise doesn't seems related to RPM more than
vehicle speed so I'm going to try to get the car up on a rack this weekend
and see if I can spot any cracks/holes in the exhaust. If not I'll let the
dealer try and diagnose it.

Thanks for the input guys.

Regards,

Gerard...

 

[Bill Putney]

I know (on paper) what CV joint is, but Ed mentioned DOJ which
I've never heard of. After some search I conclude that the Double
Offset Joint is one of the possible varieties of CV joints. Correct?

Yes - there are actually two joints on each half shaft - the outer,
properly called CV-joint, and the inner, called DOJ, or double-offset
joint. It is called that because it offsets (1) angularly (like the
CVJ) *and* (2) longitudinally (in-out - like a spline shaft) to
compensate for geometry changes as the engine and tranny move around on
their mounts and the wheels move up and down. The CVJ is usually the
one to fail because it flexes a lot more (boot tears, grease flings out,
dirt gets in, etc.) when turning corners, but the DOJ can fail too (it
turns thru a much smaller angle so boot lasts a lot longer).

Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")

 

[D.K.]

Nice to see you've got your noise sorted.

Well, I'd consider it sorted when it's fixed (and I don't go broke
in the process) ;-) But yeah, it makes so much more sense than
my original thought about engine... Besides, I have now listened
carefully and there are definitely growling sounds when turning
wheels, particularly at low speed - a sign of bad CV joint, according
to everything I read on the web.

My boots look fine so I'll have to
look further afield. The noise doesn't seems related to RPM more than
vehicle speed so I'm going to try to get the car up on a rack this weekend
and see if I can spot any cracks/holes in the exhaust. If not I'll let the
dealer try and diagnose it.

Good luck! Does the noise disapper practically the same moment you get
foot off the throttle? That's my case - even though for few seconds
RMPs and speed remains more or less the same.

DK

 

[Tony Hwang]

Hi,
Boot is torn? Then the CV joint is a toast.
Tony

 

[Carl 1 Lucky Texan]

If you do not KNOW that the boot has only been torn for a VERY short
time, then it's impractical to think you can just clean, re-lube,
re-boot the old joint. More so if it's on the right side (more dirt in
the gutter, tighter radius turns).
BUT if the boot has only recently been torn or the noise is only when
you turn or very slight when going forward - MOST cars will drive for
MONTHS like that.(wonder what percentage of FWD cars on the road right
now have undiagnosed torn boots?) But save up quickly for that new CVJ
(or rebuilt half axle) cause some day when you tromp on it you may not
move and just hear-ZZZZZZZZZZZZZZZZZZZ!

Carl
1 Lucky Texan

 

[D.K.]

Replace the half shaft.
Since you asked what a CV jopint is, I assume you don't do much of your
own work - if that's the case, best take it to a shop. Haven't done one
a few years, but I believe price (parts and labor) would run $125-$200.
Careful - there are some junk aftermarket half shafts out there. You'd
be wise to insist on one from NAPA - they seem to pay attention to
supplier quality than some of the other chains.

Yep, thanks for the advice! Went to the nearest to work shop,
explained about noises and when they called back they said
it needs new half-shaft. I ended up paying $261 of which the part
came at $119 from NAPA.

Amazing how powerful Usenet combined knowledge can be!
I don't mind paying good money for good work, but I've been burned
with car repairs more than once, and having some pre-existing
knowledge really gives some peace of mind knowing that the problem
was probably addressed correctly.

DK