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Performed · outcome unconfirmed
I can look at mine tomorrow my Indy just installed a new serp belt, alternator, Bosch, 996, rebuilt,
Leading evidence: 'Install serp belt, alternator, bosch, 996, rebuilt' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, the most frequently mentioned possible cause is 'chain tensioner' (1 discussions; 0 report identifying it and 1 suggest it). The most frequently discussed action is 'Check pulleys' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Performed · outcome unconfirmed · Original poster
I ended up replacing the alternator with a new early 997 version.
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Suspected cause
I think the problem is with chain tensioner but there was not such problem before engine rebuild.
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Suggestion · Original poster
I'll be taking the serp belt off tomorrow to check all pulleys.
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Suggestion
I would also suggest inspecting the other pullies while you have the belt off.
Counts describe captured discussions, not unique people or a diagnosis. Author identities are not reliably stored. Exact duplicate evidence is counted once across matching discussions; one discussion counts at most once per action/state. Multiple repairs reported together remain a combination. Suggestions and failed attempts do not establish a fix. Matches cover whole discussions and can include related faults, model variants and incomplete threads.
22 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
Rennlist: 1 discussions
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Generation: 20261026T191851Z · outcome-qualification-6. Deterministic extraction; no AI model inference. How we use sources
Hey All,
I've been reading this forum for years, but only recently joined - appreciate all the shared wisdom. I've been able to do a ton of repairs myself, and enjoyed the last 5 years of owning a 2003 C4 Cab.
The last couple of drives I've noticed a really ugly noise coming from the engine bay. It seems to be most pronounced at 2k rpm. I've replaced a few pulleys (idler and Ac compressor bearing) and this is not the same sound...
I posted the video to YouTube -
Porsche 996 Engine Noise
Please help.
Thanks in advance,
John
Take off the serpentine belt and test by hand each pulley, the water pump, the alternator, AC compressor and power steering pump. Likely you will find one of those is bad.
I agree with others, sounds like the one-way clutch in the alternator pulley that is making the noise.
You can replace the one-way clutch/pulley separately from the alternator, or even replace it with the Boxster solid pulley...
Its a bit fiddly getting it off (I have the same tool above). I have to try and find the youtube video where a guy shows a good method to apply pressure with two wrenches to break it free. Once it breaks free its a cinch though.
I would also suggest inspecting the other pullies while you have the belt off. The idler pullies should not spin free like a skateboard wheel. If it does, its time to replace. The tensioner pulley is kind of a pain to remove cause it has a hidden nut behind that you cannot see. The bolt on the lower idler pulley on mine snapped when torquing it back to spec. That was a headache but with a bolt extractor set that I already had and an angle drill to drill the center out, it wasn't too bad to remedy.
Great advice, thanks! That video is very helpful.
I'll be taking the serp belt off tomorrow to check all pulleys. What are the odds it's just the pulley on the alternator vs some other part within the alternator itself?
A new pulley is $90 vs $450 for a Bosch alternator!!
You've gotten good advice. IF you have to replace the alternator, the 997 version is an exact fit replacement, higher Amperage, and slightly less expensive. I posted the model numbers here:
https://rennlist.com/forums/996-foru...l#post18173549
Edit: oh, and side by side pictures here:
https://rennlist.com/forums/996-forum/1303727-996-electrical-problem-bad-battery-or-alternator-3.html#post18179480
Until today I didn't know there was a plastic cap for the alternator pully. Is mine missing or is it a MkI/MkII thing? I assume Porsche (or Bosch) had it there for a reason...
Maybe? Mines a 2001...
https://www.dcauto.com/illustrations/2903?year=2001
996 603 113 00 or 1996 603 153 50 ?
I can look at mine tomorrow my Indy just installed a new serp belt, alternator, Bosch, 996, rebuilt,
stupidly expensive
reasonable, I guess, with a 3 year 36k mile warranty, and other little parts. Maybe it has a cap.
It will through a code but it will run all day long on a defualt programing map. Its one of the ways to test the maf or associated problems caused by a bad maf.
Thanks again for all the tips. I ended up replacing the alternator with a new early 997 version. Bad noise is gone!!
As with every repair I do, there's always a lesson to learn....this one was a second lesson in the fragility of our vacuum lines. Lol. One came loose that attaches in the center-top-rear of our engine bay. Fortunately I found a line diagram online and was able to feel around for it...no way I could see it!
Hi. I have bad noise when cold start
You Tube
. I think the problem is with chain tensioner but there was not such problem before engine rebuild. I have changed one tensioner but no changes.
This protective cap is only for Tiptronic cars equipped without the free wheel locking pulley, so if your car is a 6MT this is the wrong P/N. If you have a free wheel locking style pulley the protective cap is P/N 996.603.153.50
