AdrianIreland

Hi all,

Hope someone can help.... I have a rattle that has started in my 1992 C4, one which I am very concerned about and is getting worse. Let me try as best I can to describe it.

- It's a rattle that makes my 911 sound a bit like an old VW beetle, kinda rough if you know what I mean. It's not as loud as an old beetle but it's that kind of rattle.
- It's got worse in the last few hundred miles
- It appears to be coming from the area in front of the distributor (by in front of I mean towards the rear seats from the distributor) and appears to be inside the engine (as opposed to a belt etc outside the engine)
- It happens when I am lightly accelerating or more accelerating to just keep the PRM steady. It goes away when I accelerate hard and load the engine. It happens when I rev the engine when sitting in neutral also, over 2.5k RPM
- When idling over I can hear it intermittently
- It happens anywhere from 2k to about 5k RPM, goes away after that (or maybe I can't hear it over the engine note)
- The rattle does speed up when the revs go up and it not constant speed
- I also notice that when idling over my oil pressure needle is sort of flickering slightly around the "1" mark, I don't think it did this before.

Should I get the car to my mechanic immediately? I think he is on holidays so should I even be driving it? Anyone else had this sort of issue or have any opinions on what it might be? Is the timing belt that side of the engine and could it be a tensioner on it? Fingers crossed it's not too serious....

Thanks a mil,

Adrian

Superunknown

Are you sure its not coming from underneath the engine, i.e part of the exhaust system? I know when the clips holding my heatshield broke it made a rattling noise.

boxsey911

Might be worth checking if your oxygen sensor in the Cat has worked loose in the housing. This leads to a rattle. With the left rear wheel off you can try and wiggle it - you shouldn't be able to. 22 mm spanner to tighten it up IIRC.

Make sure the exhaust is cool first

Euromagination

it's always difficult to say what a sound is if we can't hear it, but after reading the description, my preliminary guess is that it's a heat shield of some sort hitting resonant frequencies at certain RPM's...

it's happened to me on at least half of the cars i've owned...including my 964... and my Evo has a rattling heat shield right now that i have to take care of (damn spot welds)...

good luck. keep us posted...

Indycam

my cat came apart on the inside , the last section of the honey comb , it rattled around and made some noise .

Euromagination
O'my !

darth

Adrian

If it's not a loose external part (e.g. heat shield etc.) check that your cylinder bolts havn't come loose. I had a similar sound while anything above moderate engine acceleration occurred and after doing a leakdown test discovered I had 30% leakage on #3 . A retorque of the cylinder bolts fixed the annoying sound as well as cylinder oil weep. I described it as a raspy sound but after reading your description it could also be interpreted as such.

Hope this helps
Bill
90C2

AdrianIreland

Thanks everyone, I'll start looking about to see what I can find!

tbennett017

Try the old trick of using a length of rubber tubing, hold one end near your ear, and move the other around the engine compartment. This tends to focus the sound you are hearing, and you might be able to eliminate a number of options. I have an auto stethoscope, and that's better if you can find one. Ear pieces, and at the probe end is a long rod, attached to a metal kind of speaker. As you move around you can touch car parts and hear each one individually. Very valuable for diags.

In a pinch, you can do the same with a long screwdriver. Touch the tip to a component, and put your ear right against the handle.. A great way to isolate bearing noises etc.

Good luck!

PorscheZen

Perhaps i'm barking up a wrong tree but had to add my .02: Try checking the secondary muffler. Mine was cracked (on the side facing the engine) and had similar awful rasping sound btw 2K & 3K RPM. Car sounded really really SICK. People who heard it gave me weird looks.

AdrianIreland

where can I locate the secondary muffler?

boxsey911

That's the final muffler that connects directly to the tail pipe so it's on the right side of the car (regardless of LHD or RHD). This of course presumes that it's not been replaced with the short G-pipe.

AdrianIreland

Well, the rattle on mine is definitely coming from the left side.... (left as you look from the back of the car to the front that is)

boxsey911

The cat is on the left side. In addition to a loose oxygen sensor on the cat, loose insides of the cat (a very technical term ) and heat shield there is 'tin ware' around the engine that is prone to rusting and could start rattling.

tbennett017

Absolutely check all the tin ware.. expecially if there is salt on your roads.. lots of bolts to come loose, and lots of sheet metal that can start rattling... do the tube trick.. it really works.

AdrianIreland

Thanks all. I just don't like the way that the rattle gets quicker at the same rate as the RPM. The looking will start tonight!