RennBod

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!

logray

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?

RPMulli

My initial thoughts was piston slap but that typically occurs when the engine is cold...

speed rII

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.

Macster

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.

Pac996

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

logray

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.

Andrew Jackson

Here is a video of my engine noise. I know it's hard to really hear but any comments are appreciated.

https://m.youtube.com/watch?v=Js_uedmV0k0

To me out sounds like the description by the original poster. I've driven the car 15 miles with the noise but terrified of causing more damage. Car is just sitting now and I'm back to driving my minivan full time.

Hurdigurdiman

I suggest you should take it into to a Porsche Garage. You seem to be a good DIY man and have done your best. It's time to spend the big bucks. Good luck.

BBA

Really hard to tell from the video. The M96 tends to have a little bit of a ticking sound to it, which I've always assumed to be lifter noise. Did it suddenly start, or has it always been there? Other than the noise, are there any symptoms of the engine being anything other than healthy?

Exhaust noise is very possible, and in some cases will only happen when the engine is hot and the metal expands. Closely check and tighten every joint, and feel around the manifold connections for air leakage. Has any work been done to the car recently?

jumper5836

Could be drive train noise. I have the same clank, clank sound. Was only when it was cold but now it does it even when hot. Goes away when rpm's are higher.

Schnell Gelb

The clue is that the noise goes when engine revs rise. That causes oil pressure to rise.The increased oil flow and pressure fills the small (but developing) excessive clearance in the rod bearing .The debris from this bearing(I guess5 &6) will be in the filter and the pan. If you do not have a full flow filter(like LN) the debris will already be distributed throughout the engine oilways. Eventually it will plug up and reduce oil flow to other areas and the engine will self-destruct.
I hope this scenario is utter nonsense. But it was true in my case -which is why I am typing with oily fingers while taking a break from an M96 rebuild. All that saved me from worse damage was the LN filter.A magnetic sump plug will not help because the bearing material is non-magnetic.
It is easy to disprove my speculation - inspect/dissect the filter and sump plate.Post photos here if you need further dismal comment.Sorry.
You may be able to find a good used engine through Rennlist ?

BBA

He already stated that there was no material in the filter. Not arguing your point as being possible, but there are a number of less scary engine noises that are RPM specific. Most the simple rattles that I have encountered seem to be set off by a certain RPM for instance.

Macster

My advice would be to flat bed the car to a qualified shop and have a pro give a listen. In these cases the engine should be only run by a pro tech as he attempts to pinpoint where the noise is coming from. Knowing this helps him then know what is going on and what to do next.

The tech would probably pull the oil filter housing and carefully check the oil and the element for any scary metal bits.

If the oil and filter are "clean" then that kind of takes the pressure off. If not...

I hear a knocking noise and a ticking noise.

Assuming the filter housing oil and filter element come out free of any scary debris (metal or plastic or possibly rubber), the first thing that came to my mind hearing the knocking noise was water pump.

What I have offered in the past is if the noise is present at cold start to remove the serpentine belt and start the engine and confirm the noise is present or not. If it is still present the noise is coming from inside the engine. Maybe. I recall in the case of my Boxster a cold knocking noise was a loose brick in a converter.

If the noise is gone then check for any accessory drive with excessive bearing/shaft play. Most often in these cases it is the water pump but check all accessory drives. Check the belt edges, too. A belt with one (or two) sharp edges is a belt that is rubbing and it is rubbing because an accessory drive has too much bearing play which allows the pulley to be pulled out of alignment by the belt's tension.

Normally a belt even after 60K (or more) miles of use should have dull edges. There should be no contact by the belt's edges with anything.

If the noise is present only when the engine is hot, there can be a number of explanations.

One is water pump (again): My Boxster's water pump developed a grumbling noise as the cold engine warmed up. I like to believe had I continued to drive the car the grumbling could have turned to knocking.

Another source of the noise can be a converter brick is loose. While my Boxster manifested this noise cold but not hot I would not rule out a converter brick.

Might mention at this point a tech would be able to locate this noise coming from a converter PDQ.

Another source of the knocking noise can be with a manual equipped car the transmission input shaft/gears.

My Boxster doesn't manifest this noise, but my Turbo does.

With my Turbo this noise when it appears is rather pronounced. But I can make the noise go away by depressing then releasing the clutch pedal. Oh, I might mention the noise appears with the transmission in neutral and the clutch pedal fully released and the engine/drivetrain fully up to temperature.

I can make the noise reappear by revving the engine and as the engine resumes idling speed the noise is back.

While I haven't experienced this the knocking can be the dual mass flywheel. There would likely be another symptoms when moving the car off from a stop and possibly when up or down shifting.

If the noise is not from something outside the engine and present hot one has to suspect something oil pressure related. A check of the engine's oil pressure I think would be called for.

I assume the engine has been filled with a suitable oil? The right type and viscosity of oil? No 0w-30 or something weird? And that the oil level is good? And the level confirmed by during an oil change adding the specified amount of oil and not by relying upon the digital oil level system.

Really though unless you were already aware of the above (and much more) you are not the person to attempt to id the source of the noise, noises.

I repeat my advice and that is to get the car flat bedded to a qualified Porsche shop and let a pro give a listen and make the diagnosis.

The noise won't fix itself and just about any fix is going to involve a considerable (relatively speaking) sum of money (water pump for my Boxster ran around $700 (at a dealer) IIRC) so you want to be sure whatever money you spend is spent wisely.

Oh, I have not touched upon the ticking noise. But the tech would at the same time he's pinpointing the source of the knocking noise also pinpoint the source of the ticking noise. They may be related, due to the same basis underlying problem, or they may not be related. There are rather benign explanations for the ticking noise, which I won't go into here.

I think at this stage you should get a pro tech's assistance. The source of the noise (noises) may not be the end of the world and proper and prompt professional attention at this time could have the engine fixed and back on the road for a reasonable sum of money.

Schnell Gelb

Oil filter debris - you need to open up the pleats and look for very fine non-magnetic grey or bronze particles - almost an oily mud. Looking on the outside of an OEM filter cartridge does not help much.The debris will be deep in the pleats. I hope I am wrong.UOA would confirm?
You are very familiar with the lifter issue so I am assuming you determined it is not just 'soft/leaky' lifters pumping up with increased oil pressure as revs rise to 2000+. The oil-ways to the camshaft are very small diameter so are vulnerable to debris pluging.
Hoping it is something easy and simple.