baffle sound after reving. Volvo 740

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Tue 13 Apr 2004 15:16
baffle sound after reving. Volvo 740 - A2B
Hi Folks

My vehicle is 2.3l Carb petrol old volvo 740. I get a exhaust baffling sound after i rev and release the aceelerator. Mostly happens under load.

Is it serious and what could it be.

Thanks for the help
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Tue 13 Apr 2004 15:44
baffle sound after reving - Cliff Pope
If it's like the 240 there is a metal plate clamped on the exhaust downpipe, for ducting hot air into the air cleaner box. The clamp always rusts away and starts to rattle.
Or some other bit of the exhaust system loose - rubber hanger broken?
Does it by any chance have the EGR and Pulsair system? These develop leaks and faults and start to cause popping and backfires.
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Tue 13 Apr 2004 17:32
baffle sound after reving - A2B
Yeah it's kind of a poping sound a little like a backfire, I'm not really sure what the system is. It's morte like a mumbling sound rather than a loud backfire.

Thanks for the help
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Wed 14 Apr 2004 09:32
baffle sound after reving - Cliff Pope
I asked about the Pulseair system because it is famous for causing a popping in the exhaust. A colleague with a 240 with a B230 engine had it in extreme form and it regularly backfired and split the silencer.
The cure was to disconnect the rubber pipe running from the air cleaner box, through a funny black bulb, to a valve on the exhaust manifold, and pop corks in the ends. The valves usually end up failing, and it is a standard after-market mod just to disconnect the whole thing. It is supposed to inject extra air into the exhaust to burn any unburnt fuel, but it sometimes works too well.

The EGR (Exhaust Gas Recirculation) system does the opposite, and injects unburnt exhaust gas back into the inlet manifold. This is a branched metal pipe running under the exhaust manifold and round the back of the engine. When it rusts away, it can let air into the exhaust and again, cause popping or exhaust leak noise.

As I say, I am not sure whether your car has these, but it sounds from the symptoms as if it might.
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