So I've been tinkering with this issue of a metallic, pinging type sound on acceleration... No it's NOT ignition knock, or fuel knock/ping, I've certainly heard that before... My car is in great running shape, and I can't seem to figure this out. It's only when the car is moving (i.e. not just revving) and usually happens between 2500-3200 RPM.
So here is the question: Could it be my catalytic converter (my best idea...) and also, how long do Cats typically last under fairly normal driving conditions (no racing (ha), no serious fuel/engine problems etc.)


Any help is greatly appreciated!

Best,
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Spencer 1992 244 190K : Bosch LH 2.4 Jetronic FI

Mine (85 wagon) broke loose at around 150,000 mi. I replaced it and the second one lasted another 60,000. (Walker, I think)
See if you can lay under the car and get it to rattle by shacking it.
Mine did both times.

The innards of a cat do not wear out, get consumed or get clogged in normal use. They can and do last indefinitely. It can however get clogged due to an engine problem.

Also the delicate ceramic-like structure inside can break up which may cause a noise as it vibrates. This can be intermittent and happen at various rpm's. As the material moves around it can create a blockage. Sometimes the loose material can be detected by thumping the cat, it should sound solid, if there is any noise or rattle it has broken up internally and must be replaced. If the noise happens in neutral listen carefully at the cat while the engine rpm is increased.
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David Hunter

On our 93 the bracket that shares two of the large bolts that hold the M47 to the engine at the bell housing was broken where it connects to the top of the heat shield. It made a higher pitched rattling noise at about 3000 rpms. You can see the spot by opening the hood, standing on the passenger side of the car and looking very carefully at where this bracket connects to the top to the shield. Have an assistant push the exhaust system around while you watch with a good flashlight.

BTW, how many guys run their cars without this bracket connected? Our 93 was broken and so was my son's 81. On neither car was the exhaust system receiving any support from this bracket.
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Thanks for all the help. DougC. 1981 242 Brick Off Blocks, Turbo bars and wheels, M46. 1990 245, auto, 113k. 1993 245, M47, 154k.

That bracket was removed from my car before I bought it. Doesn't seem to have any real negative impact.

This is pure speculation, but I have a feeling I would have less exhaust vibration between 60 and 70 mph if it were there.


Jim
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90 244DL 263k :)

340,000 miles so far. Do they ever wear out?
Are you really sure it isn't pinking/knock ? It can be caused by carbon build-up after a high mileage, even if everything else is perfect.

My '81 has a similar noise. I thought it was pinging. I tried reducing timming to 6 degs (spec is 8 +/- 2) and going to 92 octane. No effect. One thing different than the usual pinging is the sound does not get louder if more throttle is added. I have the original cat at 290k miles but it has always passed CA smog well within limits.

or so i'm told.

Cats often make a rattling-type sound when they go bad. The baffles or whatever is inside of those things starts to break loose and rattles around inside. However, you can usually hear the noise at idle not just at certain speeds...

IMO - I would thoroughly check your exhaust system from front to back for loose or damaged pieces. As the previous poster noted, I would concentrate on the heat shields first.

A couple of other things to check:

1. Tightness of exhaust manifold bolts and especially the manifold to downpipe bolts, cat bolts too while you're at it. Look for slipping or damaged gaskets while you're there!

2. The heated air hose that runs from the exhaust manifold to your airbox. The one that supplies warm air to the engine when the car is still cold. This hose, like heat shields, can loosen, crack or even break off.


Good luck!


Jim
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90 244DL 263k :)

Can you narrow down where the sound is coming from? Does it sound like it is coming from the engine (front of the car), not from the exhaust? Is it also more of a whirring, mechanical type sound?

If so, it might be your fuel pressure regulator talking. They tend to make noise around those engine speeds, especially when the engine isn't thoroughly warmed-up yet. If I pay attention, I can hear it every time when I first get on the highway. It is a normal 240 sound, I've replaced mine once and it still makes a sound similar to the old one!

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90 244DL 263k :)

If you have 190k on the thing and it's the original cat, it's time to replace that thing.. Generally aound 150k -200k is cat time sometimes earlier depending on driving habits and climate
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-------Robert, '93 940t, '90 240 wagon, '84 240 diesel (she's sick) , '80 245 diesel, '86 740 GLE turbo diesel, '92 Ford F350 diesel dually

I dont know if this will be any help, but if it only makes the noise when you are moving then I would concentrate on the brakes or things like that. I had this problem that drove me nuts and I figured out that the emergency brake pads in the rear rotors had come lose from their shoe piece and were clanking around inside...

Have you looked at the heat shields for the cat and any mufflers?