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Old 04-01-2009, 05:13 PM   #1
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Default Light knocking sound at stop lights

Hi, I have a 1994 Bonneville SE, about 64,000 miles. What happens is that every time I am stopped at a stop sign or red light, and begin to accelerate, I get a faint knocking sound, which seems to be coming from underneath the car. I got underneath and couldn't seem to see anything loose, but I don't know too much about cars, so any information about possible causes of the problem, and how to fix it would be much appreciated. Thanks!
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Old 04-01-2009, 05:23 PM   #2
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It almost sounds like engine knock. What grade of fuel are you using? When was your last tune up with new plugs, wires, air filter, etc?

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Old 04-01-2009, 05:38 PM   #3
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I just use the regular 87 octane gasoline...I just bought the car from a dealer in December, and he told me it had been given a tune up a couple of weeks before I came in, but I obviously have no way of knowing whether that'* true or not. Is that something that could solve my problem? Thanks
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Old 04-01-2009, 11:50 PM   #4
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An SE shouldn't fuel knock @ 87 octane. Is it more of a loud tick, or an outright knock. Try putting the emergency brake on and lightly touch the accelerator. Does the knock get more pronounced? If so it'* a rod knock. Not something common in a 3.8 with that mileage but you have no idea how it was treated. Our Gearheads seem MIA tonight, Hopefully Dan or Bill will be in later.
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Old 04-01-2009, 11:58 PM   #5
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Venom makes a great point. I say it'* not the fuel either. You might have an exhaust leak. They frequently make some odd noises that sound like ticking, clicking or knocking and will only be pronounced when accelerating. If you can get the front end in the air and support on some solid jack stands. Start it, have someone power break it while adding some throttle while your underneath and try to pinpoint the noise. From the oil pan...not good. From the exhaust...better. From the trans axle...not good.
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Old 04-02-2009, 12:10 AM   #6
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Thats why I was wondering if it'* more a tick, a clank, or a knock. I had an 89 LeSabre I thought was coming apart. Turned out the cat shield busted two rivets and rattled at an idle or accelerating. I felt pretty dumb when I figured it out, tore it and the remaining rivet off and voile', no more banging. It drove me nuts for months.
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Old 04-02-2009, 12:41 AM   #7
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Dan, Sounds similar to a problem I'm having. Does it knock when you hit bumps too, & the sound is more toward one side?

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Old 04-10-2009, 11:23 PM   #8
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Possibilities:

Detonation: look for sharp edges on piston or in combustion chamber, i.e. borescope.

Any engine codes?

Exhaust leak

Exhaust manifold heat shields

Accessory belt tensioner

Valves

BTW--at 175k miles, my transmission started a ticking sound just before it failed...
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