Engine Noise
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Joined: Oct 1999
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Engine Noise
My 1990 300-I-6 (90K mi) has a sort of flapping noise at 1700 to 2000 rpm under load. Noise is worse when engine is cold, but also occurs with warm engine and cold air temp. Noise is really bad when timing is set at 10 BTDC. Retarding to about 2 BTDC makes the noise go away except when engine is cold. Any one have ideas as to where to start looking? I appreciate any help I can get. Thanks
Posting Guru
Joined: Jun 1999
Posts: 1,525
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Engine Noise
I'll say you have some sort of an exhaust leak,and,the reason is that the noise changes when you alter the timing,which also alters the sound of any exhaust,whether loud or quiet.I'll also say that it's probably not related to the exhaust manifold/gasket but the AIR injection check valve(s).These check valves will allow exhaust pressure to back flow into the AIR pipes,causing a muffled noise through out the lengnth of the pipe.If left unchecked,a faulty check valve could desintegrate the rubber hose that normally attaches to it as well as the diverter valve on the pollution pump. It's worth a check,simply pull the hose off and rev the engine,if you get exhaust out of the valve, the diaphram is shot.There is usually 1 for the manifold & 1 for the cat. conv.
Phillip
Phillip
Posting Guru
Joined: Jun 1999
Posts: 1,525
Likes: 1
Engine Noise
If there is a valve on the pollution pump, it is called the diverter valve,and,could cause a strange sound if it were bad in a certain way.Most diverter valves are mounted up from the pump,attached by a rubber hose.From the diverter valve,there will be 2 outputs,one will hook to a pipe that ultimately goes to the exhaust manifold,and the check valve is in line with the pipe. The other output will go towards the cat. converter and the check valve is in line with the tube also.Hope this helps!
Phillip
Phillip
