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DaveFromMass

1998 Rivy "knocking" and running rough - supercharger?

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Hello again. I have two virtually identical 1998 rivies, both with over 120,000 miles. They both run rough at idle and 'knock' from the top of engine (e.g. Super charger, OHC, Valves, etc.) . Both cars are tuned, new belts, new pullies, one has new alternator & water pump while the the other a new A/C compressor. The supercharger oil level is perfect. I've had a good non-rivy specialist check out the superchargers for bearing noise and that is his best 'guess' - but I am not so sure because the knocking coincides with rough idle (much like the car is skipping or experiencing mild pre-ignition detonation).

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Dave,

Generally the knocking noise at idle is caused by a worn phenolic spacer in the drive end of the supercharger. The part is less than $50. This noise really doesn't equate to an engine misfire. If your 3800 is misfiring, you should have a misfire code stored in the PCM and a "service engine soon" light on too.

Tim

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Do the 98's have issues with harmonic balancers like the 95,6 and 7's do? When I had my 95 I think the balancer had to be replaced around 110K miles, and a lot of folks on the former Riviera e mail forum wwere doing the same thing. Yes, it did feel like a rough idle too.

One thing I suggest is looking in your Advanced Auto Parts store for a mechanics stethoscope. I got mine for 3 bucks and it is the nuts for sneaking in to the bearing areaas and isolating noises. Just be careful around the spinning serpentine belts.

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John,

I think most all 3800's can have an issue with the balancer causing a noise. That Noise is usually a loud knock from the lower front of the engine. Good point and definately something worth checking out!

Tim

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Tim, I believe it is mainly the supercharged engines with this situation. I personally know of 6 other 3800's unsupercharged ,with many more than 140K miles and the balancer is still okay. Probably the kick the S charger gives it.

But in my Riv it was not easy to orient the sound to the balancer. It really worked out to a process of elimination. Of course the 95 is a different animal than the rest of the Rivs of that generation.

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THANK YOU for the info!I will try this as soon as I can. I will use my internet and personal resources to figure out to do, but this part is likely a dealer only item, so I'll hit the dealer for a copy of the replacement instructions too.

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