'97 GT Noise at At Start up

[VinGPGT]

MY 1997 Grand Prix GT Coupe with a 3800 II engine has developed a rattle/knocking noise at start up. It also makes this noise with fast acceleration. This is heard on the drivers side of the engine towards the back of the engine.

Last night my son called telling me the car(the engine) accelerated going up a hill but the car did not speed up or hold the speed. Then when I got home he said it also has a knocking noise, this morning I got to listen to the wonderful knock..... It only rattle/knocked for a couple seconds then sounded normal, but when I pressed the accelerator the knock could be heard again.

This car has 205,000 miles on it we have owned it for less than a year. No problems up to this point except the bypass elbow leaking anti-freeze. This anti-freeze leak was recently fixed.

Please let me know your ideas.

Thank you.
Vince

[doctorhrdware]

It sound like you may have spun a connecting rod bearing. It is the bearing that is on the crankshaft. Is the car running hotter than normal. When my car spun the bearing, you could hear the knocking at idle. If you would rev the engine it would get progressive louder. I also had a lose of power, it was not as strong before it was after it started knocking. I had to have the engine replaced. I had the local junk yard do the swap it was around $1500 complete.

[brcidd]

Last two I had that had a knock noise on start-up had a bad harmonic balancer- the rubber was torn away inside and making a horrendous knock- only on start-up- and slightly on shut-down... but if you hear it towards the other end- then it could be a rod...

Would be worth checking out first- and a whole lot easier to fix than a rod knock...

[tblake]

Maybe a video or audio clip would help us diagnose.

[doctorhrdware]

With the op indicating would not hold the speed going up hill or accelerate. Which is what my GP did when I spun a bearing, and it was running on the hot side.

[CrazyHorst]

I wonder if there is a valvetrain issue...?

Pushrod loads go up dramatically when going under load and speed.

Also, having the rocker covers off for a look is easier than going after a conrod bearing.

While in there i would look for pushrod that is "loose" compared to the others.

Also a valvetrain issue involving lost motion could cause power loss.

Unfortunately it will be tricky to run the engine without rocker covers (possible, looking a little ugly). What you will need are the little metal clips which prevent the oil squirts from each pushrod from arcing thru the sky and making a huge mess. Seems like I have seen these in Jegs and Summit.

If you find a related problem, you can replace the lower intake gaskets while fixing that

[tblake]

Its hard to diagnose without hearing it guys.

Wouldnt pushrod/lifter issues be consistant and not go away? Same with connecting rod bearing issues.

I've had a few 3800's with rotted balancer rubber. They would make sort of a deep metallic knock on initial startup and sometimes while accellerating. A simple test for this would be to just remove the serpentine belt and try and turn the pulley back and forth by hand. If there is any movement, its toast.

Also guys, could hook up an oil pressure guage to check oil poressure? Wouldnt lower than spec oil pressure point to a failed rod bearing?

[Fortune50]

Another possibility is the flex plate has developed a crack.

[grandprixgtx00]

Originally Posted by brcidd

harmonic balancer- the rubber was torn away inside and making a horrendous knock- only on start-up- and slightly on shut-down

that was my first impression. get a sound clip so we can listen

[VinGPGT]

Problem appears to be huge now, Friday night I towed the car home. It is knocking very bad, looks like I need a 3800.

I won't get to look at it until next week due to my ever too busy schedule. I will post something when I look at it.

Thanks for your responses, it site is full of awesome information!

[Fortune50]

Originally Posted by VinGPGT

Problem appears to be huge now, Friday night I towed the car home. It is knocking very bad, looks like I need a 3800.

I won't get to look at it until next week due to my ever too busy schedule. I will post something when I look at it.

Thanks for your responses, it site is full of awesome information!

Did you remove the plastic cover off the bottom of the bellhousing and see if the flexplate is ok? This is simple to do. Once you get the cover off, just pry on the flywheel and see if it moves around or if you can see anything that doesn't look right. Cracked flexplates is a problem that has been known to occur on these engines.