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Strange engine tic at low idle. Timing chain hardware, valvetrain?

KZOO3800

KZOO3800

New member
97 GP SE N/A 3800 Series II
178,500 miles

This is one of those things that's hard to describe but I'll try. This sounds like a little more of a dull, soft clank that changes in frequency with RPM. I'm suspecting timing chain hardware or a noisy accessory but I really don't know where to start. It started over 8 months ago and has only moderately worsened since then.

I only usually hear it at idle, and even then it kind of fades in and out. I hear it at several different intensities in a time-span as short as 30 seconds but it is always present even if it sometimes gets whisper quiet.

In trying to distinguish this from other ticking noises I've heard in person and on YouTube. The most significant distinguishing characteristic is when at idle I gently rev up to about 2500 to 3000 RPM and then quickly release the throttle: the sound reaches it's highest intensity when returning to idle. In fact, the higher the RPM the quieter the sound is. But thankfully the engine doesn't chug, sputter or stall at all when returning to idle.

Hoping to get a video of this on youtube but until then any advice would be sweet.
 


oh dear. without a good video, i would guess rod-knock... any chance u could take a vid? check your oil, is it black? notice any odd smells? hear any scraping at certain rpms/random times? loss of power?overheating? oil lights? sorry lol. alot of stuff haha. im sure there is more symptoms. if you arent having any of these symptoms, then you might be clear of rod-knock. could also be a sticky lifter. i doubt issues with timing. unlikely with chains.. i have a vid of what my 3800 sounded like when it spun. ill see if i cant find it.
 
Mine started doing exactly the same thing around 185K miles.
I couldn't hear it with the engine above 3000 rpm and it drove fine.
At 190K the oil pressure light came on at idle and shortly after number 5 rod bearing went.
Did a quick repair and at 197K #3 cam bearing ended up in the oil pan.
 


I was thinking lifter also.

What could cause the flex plate to make noise? I do know the torque converter clutch solenoid seems to be malfunctioning causing strange shifting.

I will take video tomorrow.

Sent from my PC36100 using Tapatalk 2
 
97 Grand Prix 3800 Series II Mystery Tick/Noise - YouTube

I'd driven about 20 miles right after I hopped out and recorded this. As is typical for this car the longer it's been running the more difficult it is to observe this noise. I first rev the engine a few times, then listen through the wheel well. Finally unsatisfied that this noise is audible enough for experienced forum members to observe, I try again to reproduce the noise.

In response to dsmuts suggesting this is a flexplate issue, I know I have some kind of torque converter problem. The trans still shifts through all gears beautifully for its age... but every shift into 3rd or 4th gear is accompanied by another sudden drop in RPM by 400 or 500 RPM. This sudden drop in RPM is NOT an actual shift, I've confirmed that even with the shifter in "3" it drops RPMs but doesn't shift into 4th. At anything above 3/4 throttle I can delay this 'drop' more than 10 seconds. With less agressive acceleration this RPM drop happens almost immediately. Torque converter clutch solenoid? I can't say.
 
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Reproduce Abnormal Engine Noise: Attempt 2 after engine cools for 2+ hours, includes start. - YouTube

I work 2nd shift now so I have nothing better to do than give this another shot after the engine has had time to cool for a couple hours. Shot this a few hours after I shot the first video. I began this video with the car off, pop the hood, get in the drivers seat, film the dash for a minute as I start the car, then walk to the front of the car and again manipulate the throttle for a few minutes.

I had success capturing this sound on camera this time which backs up my claim that I can usually hear this best when the car isn't at operating temperature yet. It still sounds way less audible on camera than it would to your naked ear, but just pay attention to when I let off the throttle. It's easiest to hear this noise if you're in a tight space, like a drive through at a fast food joint while you're rapidly putting your foot into/letting off the throttle.

A better description would be "rattle" but who am I to start tossing around an onomatopoeia at 4:30 in the morning...

Also, if anyone can explain this damned 'blinking' low coolant light I point out on my dash...
 
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FLEX PLATE!!! my car sounded alot like that... best way i found to check it was to turn the motor by hand from the crank with a ratchet and turn it slowly and see if you hear a metal to metal sound hard to explain!!!! but i would say replace the coolant level sensor that is on that radiator, or atleast test it to see if it works!!! hope that helps
 
Speaking from inexperience Im trying to comprehend how a flex plate or a bearing knock could create this noise and be ok for 8 months. The lifter seems most likely because I could see it taking 8 months to wear out, maybe even a loud valve or valve body hardware would last this long.

I dont think a serious knock on any bearing could have lasted this long. Also if my oil pressure is low enough to make this noise due to engine wear I think Id have seen an oil 'idiot light' on my dash months ago and already spun a bearing.
 


that vid sounds just like mine... but like bill said, 8 months is a pretty unlikely amount of time for a spun bearing to last b4 it throws it. didnt see the "8months" part originally lol. you can pull the inspection cover, and take a good look at your flex plate and see if you can spot a crack. i would guess a very very small crack if that was the issue though.
 
The sound goes away when the engine is up to temp. This means something is expanding, filling with oil etc. Can't see the vid from here, but this is the basic stuff.

Cracked flexes usually keep cracking and soon enough you'd know it. While I won't rule it out.. It's kinda like the bearing.. it's unlikely you hear it for 8 months.

Lifter.. sure a lifter might not be pumped up and when they cool it let's its oil go. Then pumps back up at start up. Easy way to tell is start the engine and if it sounds like it's valvetrain noise.. rev the engine to 2500 rpm and hold it there for 20 seconds to a minute. Does the noise go away? No.....likely it's not a lifter.

We haven't touched on exhaust leak. A crack in the exhaust would tick when cold and often close up when warm. Look at my pickup..two bolts lost their heads and I thought it was the common 5.3L piston slap w/o looking into it. A few minutes reading on a truck forum had me outside and the issue diagnosed to needed some new bolts. Ticks cold..when it warms up ... no more noise.
 
Thanks Bill all that info is helpful. The sound is always present, its just sometimes harder to hear when its warm. Im dropping the car off at my mechanics before I go on vacation Thursday. Hes gonna do a complete vehicle inspection and he owns his own trans shop so well see what he can find.
 
When I got there to drop off my car the owner informed me he and all his mechanics were tearing out fire damage and preparing to knock down /rebuild the back half of their facility. They can't do any work til Wednesday bc there was a huge fire a day or 2 earlier... yikes.

I was surprised when he told me to pull in the front of his shop so he and 3 of his guys could check out my engine. What a guy. After 10 minutes of revving, shifting and several brake torques they all but ruled out any bottom end knocking.

Their 2 cents: Pretty certain its a top end issue or possibly even a worn out accessory, does not appear to be flex plate issue at all. Valvetrain is suspect. Unanimously agreed that knock and/or flex plate problem would have killed this engine long ago.
 


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