996 3.4 engine trouble

[Achlex]

Hey guys,

 

My 996, a late 98 3.4, started to exhibit a strong knocking sound coming from the driver's side of the engine. It's the dreaded "sounds like a lifter" type of knock. Very audible at idle, gets faster & louder as revs increase (haven't revved it past 2.5k):

 

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I did push the car fairly hard a few hours earlier, though for a very short period of time (basically merged from 40-150+ and backed off, engine fully warmed up). No overheating or oil pressure issues. The car was running fine coming home, I have a small garage so I would have heard anything backing up with the windows down and the sunroof open. Started it up three hours later, and the noise appeared within 500 yards. I didn't do anything to the car in between save for a mod on the PSE relay (cutout delete), which seems unrelated. 

 

Also, the car just spent 3 weeks in the shop for a new IMS / clutch, and cylinder #6 was bore checked, with no evidence of scoring found. One of the chain tensioners was also swapped for a good used unit. The oil is brand new (<150 miles), the oil level hasn't changed, and oil pressure is still good (4.5 bar cold). There also isn't a single code on the ECU.

 

The tailpipes are a bit black on the inside but there's no oily residue in them, nor is there any on the bumper. Overall, this is a very clean car with a full service history, low miles (45k), and "only" four prior owners in 25 years, though it was seldom driven in the past 10 years (6000 miles or so).

 

I didn't have it towed yet but showed a video of it to a couple of shops, both of which were sort of expecting a full rebuild would be needed. Interestingly, one said he found most cases of catastrophic engine failures he sees happen within weeks / months of a car changing hands. 

 

In any case, I'm looking for any kind of input / help, but will also accept empathy and Porsche reliability jokes.

 

BR, 

Edited August 7, 2023 by Achlex

[judgejon]

Main bearing?

good luck…

[JFP in PA]

Time to pull the oil filter and look for metal debris......................

[Achlex]

Can you remove the oil filter with the engine still full? Or do you need to drain it first? 

[JFP in PA]

Yes, the filter contains 1/2 to 3/4 of a quart of oil, the rest will remain in the engine.

[Achlex]

Hey everyone, 

 

Issue turned out to be a collapsted lifter. It went right back up after an oil change. No debris in the filter. 

 

I will keep a close eye on how it runs in the coming months!