2002 Grand Prix SE -- Knocking Sound

[JP32]

Hey All --

I've been hearing a knocking sound coming from my Grand Prix's engine (I think its the engine). I can hear it more clearly when the the hood is closed, or if I put my head down by the wheel-well.

Sometimes it is louder then others, and can get quite loud... but it definitely happens while in park, and in Drive.

I took it to a general mechanic, and he thought it was a transmission problem, and sent me around the block to a guy who's good with transmissions.

This mechanic was in a rush (didn't have an appointment with him, the original guy just sent me over), but he took a quick listen. He thought that it was NOT coming from the transmission... and that he's heard that sound in a lot of GM cars, and that it probably isn't a big deal (clearly, he doesn't understand my luck).

Anyway... that's about all the info I have on it... anyone have any ideas on where to point me? I'm not the type to work on my own car past changing tires... but I'd definitely like to have some more knowledge next time I talk to a mechanic.

Thanks guys!

(I searched this before I posted, but nothing seemed to match exactly what I needed... sorry if this is a common question).

- Joe

[BNaylor]

Welcome to AF.

It would help to post your mileage. The 3100 V6 engine may suffer from piston slap at initial startup but a knocking sound if internal engine noise is abnormal

[JP32]

Thanks for the reply!

The Grand Prix has 92,000 miles on it.

Not sure if it matters, but when I mentioned that I can hear it well when I put my head next to the wheel, I was talking about the front-driver's side.

[tblake]

I agree with Bob, the 3100's have piston slap issues from day 1.

Does the knock get quiter or go away as the car warms up?

[JP32]

I would lean toward saying it gets louder.

Let me give an example:

When my wife drives home from the store, and I open the front door to go out and help her carry in the groceries, I can easily hear this sound from the car from 30 ft away, and it sounds pretty bad.

But when I open the hood to take a listen, it's harder to hear... as if the general engine noise kinda drowns it out... but when I close the hood, I can hear it more clearly again.

Another little thing...

When I showed the first mechanic the problem, he had me put the car in drive... and the sound got louder. He told me to take it to the transmission guy (like i mentioned above) who was less then a tenth of a mile away... when I put it in drive for him, the sound seemed to get lower! I just don't get it.

[tblake]

Take the serpentine belt off and run it like that for a minute. tell us if the sound get better.

[JP32]

Sorry for the long delay...

In case anyone is curious, we found that the circular piece of metal that holds the transmission to the engine has a crack in it, and that is what's causing the noise.

The mechanic quoted us $550 for labor, as it's an 8 hour job. Does that seem right to you guys? Just seems a little steep to me.

[grandprixgtx00]

Originally Posted by JP32

Just seems a little steep to me.

not really. If I'm thinking of the right part, you gotta drop the whole K-frame prop the engine up and drop the tranny. PITA job for sure

[Jrs3800]

Did we ever figure out what engine this is?

I know some of the 3800's have fractured( Cracked ) a flywheel... Is this what the mechanic was talking about?

[grandprixgtx00]

Originally Posted by Jrs3800

Did we ever figure out what engine this is?

the OP's car is an '02 SE which only came with the 3100

[richtazz]

I would say it's the flywheel he's talking about, and that labor amount isn't bad at all. As grandprixgtx00 stated, you have to drop the trans to change it.

[JP32]

Hey all --

Finally got it fixed... it was the flex plate (which in my limited knowledge is just the automatic-transmission version of the flywheel). Noise is gone, what a relief!

Thanks for the confirmation on the price, Rich and GP.

And yes.. GP is right... engine is a 3100.