Dharn55

I had a 76 911S, supposedly the worst of the thermal reactor engines. Had over 120,000 miles on it when I sold it. It did have the chain tensioners collapse once on a trip to Florida, caused damage to the IMS sprocket (yes they did have IMS's) which meant the cases had to be split and a new IMS installed. But the studs never pulled. I know that the engine was finally rebuilt after 150,000 miles as I saw it at the shop. But I don't know why the rebuild was done.

philooo

Knocking with a hammer was not very conclusive, the sound is not really different from cat1. On the other hand, I noticed that the sound is a lot louder when the engine is fully warmed up.

After a drive I use the screwdriver handle to ear trick and again the sound coming from cat#2 was, without a doubt, knocking whereas the cat#1 was not making any sound.

If anything, what's for sure it is on the bank#2, at least..

Eharrison

I'm throwing this out there with nothing to back it up but there's no moving parts on the cat right? I think you noise is telegraphing into the cats from Bank 2

philooo

yeah i might get back under the car this weekend and try to poke a little more to the engine with the screwdriver/ear thing, trying to make sure the clicks are not coming from somewhere else. I just hate to get under the car too far, and so far I have not place the screwdriver onto the transmission, will do it this weekend.

Eharrison

The only thing near your transmission that is turning while in neutral is the throwout bearing. That is not a throw out bearing noise. (unless your bearing is square.)

Tippy

I doubt it is but man that sounds like a spun rod bearing. That hollow metallic sound makes me think that. But, it is a little too fast I believe to be that.

Dharn55

If it was a spun rod bearing I would think you would hear the noise with the screwdriver trip pretty equally on both sides. You should be able to further isolate the noise by listening at the cat and then at the head. If you don't hear the noise as clearly at the head as at the cat then it is probably the cat. There are not supposed to be any moving parts in the cat (or the mufflers) but the internal baffles do come loose and make these type of rattle. Not al that uncommon.

roadsession

I had a very similar noise:

https://rennlist.com/forums/996-foru...s-not-ims.html

philooo

Did you try the 'screwdriver to ear' trick ?

I did point the screwdriver onto my headers today, the clicking noise is quite similar to when it is pointed onto the catalytic converter....

Can the noise propagate from the cat. to the header ?
Did anyone had this problem and try to listen to it that way ?

I 'feel' that the noise is a little lower on the header than the cat. but the volume is pretty close +- 15%. I really cannot tell.

philooo

One more thing, if I decide to go to the dealer to make them replace the catalytic converter under the EPA wanrranty I assume I have to remove my FisterD mufflers ? or they are ok with that kind of thing... I think I know the answer but I wonder if your dealer ever gave you crap for this mod.

smorris

With the CEL light on and the cat efficiency code you cleared previously the dealer would "love" to replace the cat at full price and charge off to warranty!

After clearing the code, my CEL will come on after driving, sometimes not for a few days but it will come on...

It is really hard to "armchair" diagnose a car from a video, but a cat rattle "usually" has a sound rattly-gravely sound that will often clear with higher revs...

If you warranty covers all internally lubricated parts, I would drive it until the CEL light reappears or the egine grenades...doesn't sound comforting, but unless you are willing to pay the price for a partial teardown you will have to wait for one or the other to have it covered!

My first cat went bad 45 days outside of the 8 year inservice date so the dealer told me I was out of luck!

**and your warranty should cover a rental, so you could be the proud driver of a late model Toyota camry or some other fleet car for a week or more!

15psi

I had a similar noise. My first thought was a bad lifter. It was difficult to tell where it was coming from. (I used an electronic stethoscope) Sometimes it was more noisy that others. Turned out to be a VERY loose spark plug. It was backing itself out. Middle plug on passenger side. The rest were barely hand tight. Appeared to be original plugs a 100k.
Nice and quiet now and runs better (did alot of other upgrades at same time)

https://rennlist.com/forums/996-foru...ed-engine.html

redridge

yes, but the noise is not coming from the headers, that is a mechanical noise and it could be coming from the exhaust manifold end or even further upstream... Hopefully it is downstream (bad cats), but I had a bad cat and didnt make any noise at all.

15psi

Mine didn't either. I put the car on the lift and with the listening device, it appeared to be coming from many areas of the engine - could not pinpoint. I would not of guessed plugs based on the noise. And this is a common problem on these cars.

2fas4u

You said the oil was in need of changing, change to a heavy oil like 10w 40. Add one quart of lucas stabilizer if the noise lessens the you know you've an engine problem if it's the cats this will not help.