: Slight knock during acceleration?



06BlackV
06-08-12, 11:29 AM
Ok fellas, i have the ls2 motor, 70k miles and it makes a Knocking noise only when accelerating. Its a deep knock kind of a rod knock but alot quieter, the windows have to be rolled up and radio off in order to hear it. It sounds like its coming directly below the center console area. Any ideas where to begin my diagnosis? Thanks

PISNUOFF
06-08-12, 01:13 PM
See if the frequency changes with engine speed (rpm) or with road speed (mph).

lollygagger8
06-08-12, 01:41 PM
Shitty gas?

Cadillac Cust Svc
06-08-12, 03:27 PM
Sorry to hear that, 06BlackV. We recommend consulting with your dealership for an initial diagnosis, but if you're more of a DIYer, I can appreciate that! Please feel free to send me a private message if you ever want me to investigate any questions you may have while going through the process. I can always double check my resources on your behalf!

Have a great weekend,

Katie
Cadillac Customer Service

06BlackV
06-08-12, 06:28 PM
See if the frequency changes with engine speed (rpm) or with road speed (mph).

The frequency changes with Rpm but stops knocking when i pass 4k rpm :/

06BlackV
06-08-12, 06:29 PM
Shitty gas?

Ive been through about 15 different fill ups since this issue has been going on.

Motown Cad
06-08-12, 06:38 PM
06 I swore I had a knock (100k) but tell me this, does it get less pronounced after two to three minutes? If so, I'm almost certain it's cold factory headers. This engine took some getting used to. I've heard some refer to our top ends as sewing machines which made me laugh. But it was hard trying to diagnose that sound with the injectors and coil pack noise going off. Now if I run 89 and let er rip, I will sometimes hear valve knocking/flutter sounds and that is very discernible. If I put 93 and some octane boost in, it wont happen. I'm not crazy about the engine sound, but that's why I stomp on the gas. To hear the exhaust. Plus a K&N CAI with the flap removed will create a nice loud sucking whistling sound to mask it lol.

06BlackV
06-08-12, 07:10 PM
06 I swore I had a knock (100k) but tell me this, does it get less pronounced after two to three minutes? If so, I'm almost certain it's cold factory headers. This engine took some getting used to. I've heard some refer to our top ends as sewing machines which made me laugh. But it was hard trying to diagnose that sound with the injectors and coil pack noise going off. Now if I run 89 and let er rip, I will sometimes hear valve knocking/flutter sounds and that is very discernible. If I put 93 and some octane boost in, it wont happen. I'm not crazy about the engine sound, but that's why I stomp on the gas. To hear the exhaust. Plus a K&N CAI with the flap removed will create a nice loud sucking whistling sound to mask it lol.

LOL i got the intake sounds but this sound doesnt go away when hot :/

Motown Cad
06-08-12, 09:24 PM
Oh ok. Did you by chance do a blackstone oil analysis yet? I'm not sure if that would show valve train wear. That's one example of non invasive trouble shooting. I have to do mine again to get baseline. I only had a few ppm above normal on cylinder wall metal and they said that was indicative of "spirited driving" nyuk nyuk.

Mike

06BlackV
06-09-12, 01:06 AM
Oh ok. Did you by chance do a blackstone oil analysis yet? I'm not sure if that would show valve train wear. That's one example of non invasive trouble shooting. I have to do mine again to get baseline. I only had a few ppm above normal on cylinder wall metal and they said that was indicative of "spirited driving" nyuk nyuk.

Mike

Where can i get an oil analysis? And at what price?

JDB
06-09-12, 10:17 AM
www.Blackstone-labs.com

Click the free sample kit, follow directions. Info page and FAQs for any further questions. $25. +10 if you want the TBN done if you want to see if additives are still left to help determine if you can extend drains. Cant hurt the first couple times.

Please post your results.

darkman
06-09-12, 10:50 AM
Ok fellas, i have the ls2 motor, 70k miles and it makes a Knocking noise only when accelerating. Its a deep knock kind of a rod knock but alot quieter, the windows have to be rolled up and radio off in order to hear it. It sounds like its coming directly below the center console area. Any ideas where to begin my diagnosis? Thanks

Your description leaves open numerous possibilities. It could be low oil pressure, detonation (spark knock), excess rod bearing clearances, excess crankshaft bearing clearances, failing motor mounts, or even a deterioating dual-mass flywheel.

06BlackV
06-09-12, 02:19 PM
Your description leaves open numerous possibilities. It could be low oil pressure, detonation (spark knock), excess rod bearing clearances, excess crankshaft bearing clearances, failing motor mounts, or even a deterioating dual-mass flywheel.

Oil pressure is 33 at idle when hot, 46-50 while casually driving. I have the ls7 clutch kit with ls7 flywheel.

darkman
06-09-12, 04:07 PM
Oil pressure is 33 at idle when hot, 46-50 while casually driving. I have the ls7 clutch kit with ls7 flywheel.

That obviously eliminates the dual-mass flywheel and oil pressure. Bearing problems coincide with with low pressure, which you do not have. Based on the your description of a "deep knock" would also make detonation (spark knock) unlikely. The motor mounts remain a possibilty since motor shifting is also associated with acceleration. The stock mounts leak brown fluid which stains the surrounding motor parts. Beyond that I am not sure what else to check.

JFensty
06-09-12, 05:52 PM
Older water pumps used to "knock" when the bearing was going out. ??? Have you used a stethoscope?
Edit: I reread the first post. If its coming from the console area could be the throw out bearing. I know you said out was replaced but could be that or a finger on the pressure plate.

06BlackV
06-09-12, 08:58 PM
Older water pumps used to "knock" when the bearing was going out. ??? Have you used a stethoscope?
Edit: I reread the first post. If its coming from the console area could be the throw out bearing. I know you said out was replaced but could be that or a finger on the pressure plate.

I was thinking the throw out bearing as well, im afraid when they installed my clutch , they didnt do something right or damaged something in the process:/ the noise is very mild i didnt really notice it till about a week ago because i always have music playing or windows down so i wasnt able to notice the noise.

06BlackV
06-09-12, 08:59 PM
Thanks you Darkman, ur the "Go to guy" on these forums i see

Motown Cad
06-10-12, 02:06 AM
Darkman, The oil analysis would rule out any bearing issues if ppm is good right? I would do it anyways just for a cheap snapshot of internals and the peace of mind.

darkman
06-10-12, 10:24 AM
Darkman, The oil analysis would rule out any bearing issues if ppm is good right? I would do it anyways just for a cheap snapshot of internals and the peace of mind.

An oil analysis can definitely indicate the general health of the internals based on the level of metal traces. At one time or another I have used oil analysis on almost every engine I own.