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Old 02-22-2012, 10:28 AM   #1
RennBod
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Default Engine noise when warm, fine when cold!

Hi,

I have been a member of rennlist for a few years now, and moved around various models in this time, everything from a 924 through to a 993 and a couple of 996.

At the moment I have a 3.6 996 which is really worrying me.. Not that owning it worries me, its more the noise its making once its warmed up, it is fine when cold... the noise also seems to fade in and out in volume a bit.. from being very quiet tap tap, through to quite loud clack clack clack.

If the rpms are increased to 2000 rpm, the noise goes away..

I first noticed the noise a couple of weeks ago, a tap tap tap (or click click click) from the right hand side of the engine (from being standing behind the car). I decided it was the lifters, so I bought some tools, including cam locking tools, and set about changing the lifters on that side.. all of them..

Once it was back together... same noise...

Oil pressure seems to be at 1.5 Bar with the engine hot, so I think thats ok!

The lifter cradle seemed to have no scores or signs of wear.. the cam also looked just fine (no worn out lobes)

I have listened everywhere around the engine with a stephoscope, and even removed the air con compressor, so I could listen around that area..

It seems to be loudest, listening from the top of the engine, at the cylinder closest to you on the right hand side, as you look through the engine cover, possibly bellow the intake port.

At worst the sound is a loud clack clack clack, like a worn out camshaft on an overhead cam engine, at best it sounds like a very quiet tap tap a little like an aircooled 911 engine that has a tappet/follower needing adjusting.

I have performed a leakdown test, and the readings were just fine.. if I disconnect the injector from that cylinder it runs rough, so I know the cylinder is firing.. no coolant loss, oil level is fine and oil has been replaced (5w40 at the moment) the oil filter has no debris in it and everything else seems to be fine.

erm.. not sure what else to say, or what else to do.. except cry out "HELP!" :o)

Apart from when I am looking for the noise, the car is not being driven or used.. it just runs occasionally so I can investigate the noise some more.

again... HELP!
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Old 02-22-2012, 12:17 PM   #2
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A bunch of guesses for you. Begin the internet guessing game!

#4 then? Compression good?

Did you try swapping spark plugs and coil packs between cylinders to see if it follows?

Any DTCs or MILs or CELs?

What do the plugs look like?

Did the noise go away when you unplug the injector (or disable the cylinder in software/Durametric)?

Sleeve starting to give way?

Can you post a you tube?

On a 3.4L I would say variocam actuator is gone, but the 3.6L is different design... still though perhaps it could be. Have you tried actuating the variocam actuators, or swapping them between banks?

Worn intake guide and excess valve noise/oil combusting noise?

Where was the air leaking through on your leakdown test, and what were the numbers?
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Old 02-22-2012, 12:34 PM   #3
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My initial thoughts was piston slap but that typically occurs when the engine is cold...
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Old 02-22-2012, 03:11 PM   #4
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Take out the sparkplug at cyl #4.
Put long rod thru the sparkplug hole and rotate engine to tdc, keep the rod against the piston and rotate engine until you feel the piston going down.
Stop rotating and push the piston with the rod. Now if there is too much play in the rodbearing you will feel it or even hear it as a clunk.

Fast way to check the rodbearing or loose rodbolt.
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Old 02-22-2012, 03:33 PM   #5
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Quote:
Originally Posted by RennBod View Post
Hi,

I have been a member of rennlist for a few years now, and moved around various models in this time, everything from a 924 through to a 993 and a couple of 996.

At the moment I have a 3.6 996 which is really worrying me.. Not that owning it worries me, its more the noise its making once its warmed up, it is fine when cold... the noise also seems to fade in and out in volume a bit.. from being very quiet tap tap, through to quite loud clack clack clack.

If the rpms are increased to 2000 rpm, the noise goes away..

I first noticed the noise a couple of weeks ago, a tap tap tap (or click click click) from the right hand side of the engine (from being standing behind the car). I decided it was the lifters, so I bought some tools, including cam locking tools, and set about changing the lifters on that side.. all of them..

Once it was back together... same noise...

Oil pressure seems to be at 1.5 Bar with the engine hot, so I think thats ok!

The lifter cradle seemed to have no scores or signs of wear.. the cam also looked just fine (no worn out lobes)

I have listened everywhere around the engine with a stephoscope, and even removed the air con compressor, so I could listen around that area..

It seems to be loudest, listening from the top of the engine, at the cylinder closest to you on the right hand side, as you look through the engine cover, possibly bellow the intake port.

At worst the sound is a loud clack clack clack, like a worn out camshaft on an overhead cam engine, at best it sounds like a very quiet tap tap a little like an aircooled 911 engine that has a tappet/follower needing adjusting.

I have performed a leakdown test, and the readings were just fine.. if I disconnect the injector from that cylinder it runs rough, so I know the cylinder is firing.. no coolant loss, oil level is fine and oil has been replaced (5w40 at the moment) the oil filter has no debris in it and everything else seems to be fine.

erm.. not sure what else to say, or what else to do.. except cry out "HELP!" )

Apart from when I am looking for the noise, the car is not being driven or used.. it just runs occasionally so I can investigate the noise some more.

again... HELP!
Is the noise very closely related to engine speed or does it appear to be then appears to not be?

Is the noise coming from inside the engine or outside?

One trick is to remove the serpentine belt and run the engine to determine if the noise is coming from the belt drive or accessories or coming from inside the engine.

Trouble is the noise occurs only when the engine is hot.

You can still do the test. But you have to limit the amount of time you let the engine idle. A few seconds, 10 maybe, ok. Beyond that... BTW, these numbers are not based on direct experience. But 10 seconds at idle will not subject the engine to that many power cycles and thus raise the coolant temperature all that much.

While you removed the injector and the engine ran rough, the real test is to disable each cylinder in turn and note the amount the idle rpms drop. The cylinder that is disabled and the rpms drop the least is the weakest cylinder.

The engine has not manifested a CEL so the engine controller (DME) has not detected any misfires. Misfires most often are flagged when the DME detects a weak/underperforming cylinder.

Now you may not have driven the car enough or subjected it to the driving conditions which can bring forth misfires. But I'd not advise you to drive the car more just to see.

Another possible cause is there's an exhaust leak. These can sound like a mechanical noise but of course aren't. Sometimes the noise is present cold and goes away as the exhaust heats up and the crack closes. But there's the possibility the crack or split is closed when cold and opens up as the exhaust heats up.

You need to be under the car (safely!) with it running and carefully checking for exhaust leaks. Be mindful of where you put your hands. Everything is hot under there and if you touch something hot and ****** your hand away and it gets into the serpentine belt you'll wish all you had was an exhaust burn.

You say you changed all lifters on the suspected bank? Did you carefully inspect the springs for a failed one?

When you removed the camshaft cover did the cover's sealant look ok not only around the edges but around the equally critical pads that have the oil holes that supply oil to various things up there? An internal oil leak can 'starve' a lifter or a subset of lifters of oil yet the oil pressure at the pump can read ok.

Let me think on this some more...

Sincerely,

Macster.
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Old 02-22-2012, 07:02 PM   #6
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Quote:
Originally Posted by Macster View Post
Is the noise very closely related to engine speed or does it appear to be then appears to not be?

Is the noise coming from inside the engine or outside?

Another possible cause is there's an exhaust leak. These can sound like a mechanical noise but of course aren't. Sometimes the noise is present cold and goes away as the exhaust heats up and the crack closes. But there's the possibility the crack or split is closed when cold and opens up as the exhaust heats up.

Let me think on this some more...

Sincerely,

Macster.
My first guess is exhaust leak. Try just wrenching any bolts and nuts a little. If any turn you know where to double check again if the noise appears again.

Go after where the headers bolt to the heads. This is where you get the noise exactly like a lift noise when there are leaks. May I suggest doing it when the engine is cold
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Old 02-22-2012, 10:05 PM   #7
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Interesting is it's fine when cold, and shows up when hot.

If it's an exhaust leak, plug, etc. it's probably going to manifest even one cold. Sounds like something mechanical to me, but this is fun to guess, isn't it?

Guessing this problem was present before/after the lifters.
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Old 02-22-2012, 10:05 PM
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