I've had a really annoying rattle coming from the rear of my c4. Finally got round to looking at it yesterday, and found that, with engine running, the rattle stopped when I pressed upwards on the plate under the far left of the car. Tightened the bolt a little, stopped the rattle.

As soon as I had driven the car for a few minutes, it returned.

Can I take this plate off completely to see if that is the problem, and anyone got any ideas on what else it could be?

Thanks

 

Hi,

Yes this is a real problem with the undertray- they seem to rattle everywhere. Lie underneath it and tap it with your hand, you will quickly find where the loose parts are. Tighten all of the bolts, making sure non are missing, replace if they are, also check the plastic tray over the transmission, this can work loose as well.
The Cat. cover can be loose as well.

Good luck

Ade.

 

Many on rennlist would say yes, take it off; -take it off, and leave it off. Some say they take them off for summer, and replace them for cold weather. Removal will allow the engine to run cooler. Bruce Anderson suggested we do that for our 964s and 993s (although 993s have somewhat smaller trays) after noticing premature heat-related engine wear. It's ok to remove it to see if that cures the rattle even if you don't want to leave it off.

 

Last week I finally decided to figure out where the rattles where coming from on my C4 Cabriolet.

I found one missing bolt missing from the "tin" surrounding the cat. It turns out that one of the brackets welded to the cat had broken off. (My car is lowered and I probably slammed the cat on a speed bump or leaving a steep incline) I'm going to have to remove the cat and have that flange welded back on.

Further inspection turned up a missing bolt. One of the bolts that holds the cat to the heat exchanger is missing.

I also found that one of the lock nuts was completely stripped and needs to be replaced.

I went to the MS Road Race site and pulled up the exploded diagram of the exhaust system and headed over to the Porsche dealer and ordered the necessary supplies.

A first, I thought about removing most of that tin, but decided against it. (Porsche doesn't put things on the car without a d*mn good reason) I speculated that the intense heat from the cat would have a negative impact on the left rear tire and/or the shock absorber.

Any comments on the effects of increased heat cause by removing exhaust tin?

Terry R.
'90 C4 Cabriolet
<a href="http://www.p-caronline.com/directory/c4_guy/" target="_blank">http://www.p-caronline.com/directory/c4_guy/</A>

 

There is an aluminium plate pop riveted into the undertray. These rivets corrode and break causing rattles. Drill out and replace.
As for removing it for the summer...er what summer?

 

The undertray is a worthless piece of junk. It collects rocks & debris which rattles, collects moisture and holds that right up against the engine, thus promoting rust. Take it off, and award it to the next owner.

 

So I guess that my weekend is going to be spent checking bolts rather than driving

Is it just me, or are other owners paranoid about "new" noises from their car? I tend to forget that it is 11 years old and might be expected to have the odd rattle and squeak, and worry too much about finding and fixing them!

 

Brad was your problem with the actual undertray or was it the tin that surrounds the catalytic converter?

"pressed upwards on the plate under the far left of the car"

Based on your description, I assumed that you were having problems similar to mine - with rattling cat shielding. If it's the actual undertray itself, the suggestions for removing the undertray are good advice. I removed mine quite some time ago.

 

erm, not too sure. It is the tin underneath the cat, but it does not appear to be attached to the cat. I thought that it was a smaller undertray panel.

Cannot find a diagram of the undertray on the web - got any ideas?

 

Here's a diagram of the exhaust system. You'll see that parts #20, #24, #25 are all the tin bits that surround the cat. If you break or lose one of those nuts, the tin will rattle.

You're absolutely right - the tin doesn't look like its attached to the cat. It is though - there are flanges welded onto the cat itself and the surrounding tin bolts to it. (I bottomed my car out and broke one of those flanges off & need to have it welded back on.)

Terry R.
'90 C4 Cabriolet
<a href="http://www.p-caronline.com/directory/c4_guy/" target="_blank">http://www.p-caronline.com/directory/c4_guy/</A>

 

yep, thanks for the diagram - it is part 20 that rattles. I'll have to get it off and look at all the bolts etc.

Will post a progress report on Monday.

 

Just posted a reply to anotherr thread - was the cat shield that rattles due to sheared bolts. Taken it off and all is fine, but now need to find some bolts to refix it!