Misfires, spark knock and hissing sound. Related? - Camaro5 Chevy Camaro Forum / Camaro ZL1, SS and V6 Forums

EJSS · 09-29-2021, 08:37 PM

Hey car geniuses I got another for you..My L99 has been lacking power at low rpms when in both closed loop and open loop. It feels and sounds slightly off. I also heard a slight tapping sound that sounds to me like spark knock around the bank 2 exhaust manifold area. I'm getting about a degree or 2 of knock retard, only for a couple of seconds at a time, usually when I give it some gas. The knock also happens while I'm cruising, but it's less frequent. I also hear a pretty loud hissing sound coming from the driver side of the exhaust manifold, but I'm not sure if this hissing is normal or not. Could it be just a hissing from the evap or fuel rails or is it likely from a vacuum leak? Not getting any codes, already replaced all spark plugs and checked my exhaust for leaks/clogs. The only other strange thing is my evap test is not passing, but it's not setting a code either. The evap test conditions have been met 7 times but the test hasn't passed yet.

Is the hissing normal for the L99 on the driver side? Any other ideas? Thanks.

EJSS · 09-29-2021, 08:38 PM

Only mods are z28 air intake and high flow cats. No tune. This problem just started out of nowhere.

Risingson05 · 09-29-2021, 09:28 PM

Can you post a vid ? Does the tapping noise get louder when accelerating?
Knock sensor listen for knock so they can pull timing .
As far as the hissing sound could be a vacuum leak to exhaust leak a lot of different types of hissing noises

09-29-2021, 08:37 PM	#1
EJSS Drives: 2010 Camaro SS L99 Join Date: May 2019 Location: New Orleans Posts: 119	Misfires, spark knock and hissing sound. Related? Hey car geniuses I got another for you..My L99 has been lacking power at low rpms when in both closed loop and open loop. It feels and sounds slightly off. I also heard a slight tapping sound that sounds to me like spark knock around the bank 2 exhaust manifold area. I'm getting about a degree or 2 of knock retard, only for a couple of seconds at a time, usually when I give it some gas. The knock also happens while I'm cruising, but it's less frequent. I also hear a pretty loud hissing sound coming from the driver side of the exhaust manifold, but I'm not sure if this hissing is normal or not. Could it be just a hissing from the evap or fuel rails or is it likely from a vacuum leak? Not getting any codes, already replaced all spark plugs and checked my exhaust for leaks/clogs. The only other strange thing is my evap test is not passing, but it's not setting a code either. The evap test conditions have been met 7 times but the test hasn't passed yet. Is the hissing normal for the L99 on the driver side? Any other ideas? Thanks.

09-29-2021, 08:38 PM	#2
EJSS Drives: 2010 Camaro SS L99 Join Date: May 2019 Location: New Orleans Posts: 119	Only mods are z28 air intake and high flow cats. No tune. This problem just started out of nowhere.

09-29-2021, 09:28 PM	#3
Risingson05 Drives: 2015 zl1 m6 Join Date: Jan 2020 Location: Alaska Posts: 702	Can you post a vid ? Does the tapping noise get louder when accelerating? Knock sensor listen for knock so they can pull timing . As far as the hissing sound could be a vacuum leak to exhaust leak a lot of different types of hissing noises