NEED HELP! Engine sound advice
Thread Starter
Intermediate
Joined: Mar 2011
Posts: 39
Likes: 0
From: West Hartford CT
NEED HELP! Engine sound advice
I am looking at buying black 2005 z51 which i took for a test drive on monday. The price is right, but the one thing i noticied was that when i got on the throttle in 3rd gear there was a litle bit of what sounded to me like an engine knock. There were no unusual sounds at idle or when driving casually around town.
The owner had the belt changed recently because he said that it had been squeaking. I pulled all of the codes on the car with my scan tool and found nothing current but a couple of old codes. one was for the MAF and the other was a body control system error.
Could this be the harmonic balancer issue or just low grade fuel? I wouldn't mind fixing the balancer, i'm just afraid it could be something worse. I also know i am really sensitive to sounds so maybe i am just making myself crazy
The owner had the belt changed recently because he said that it had been squeaking. I pulled all of the codes on the car with my scan tool and found nothing current but a couple of old codes. one was for the MAF and the other was a body control system error.
Could this be the harmonic balancer issue or just low grade fuel? I wouldn't mind fixing the balancer, i'm just afraid it could be something worse. I also know i am really sensitive to sounds so maybe i am just making myself crazy
Melting Slicks
Joined: Sep 2008
Posts: 2,286
Likes: 4
If it walks like a duck and sounds like a duck it's usually a knock in this case. Sorry to make light of it. If you know someone with HP Tuners, maybe they can scan your car to see if it's engine knock.
Jeff
Jeff
Thread Starter
Intermediate
Joined: Mar 2011
Posts: 39
Likes: 0
From: West Hartford CT
Usually i would agree. The thing that is confusing me is that in the times that i have seen knock because of an internal componant it doesn't seem to matter what the load is on the engine. Load or not the engine would knock. This sound only happened heavy acceleration in 3rd gear (possibly other gears, i didn't have the opportunity to check)
Race Director
Joined: Oct 2010
Posts: 14,475
Likes: 786
From: Las Vegas NV
How long did you drive it? Did the oil temp get to over 100º? My '05 has always had a slight knock when it's cold and it goes away completely when the oil temp rises. At idle I can't hear it. When the temps were really cold a couple months ago it almost sounded like a diesel. Now that it's warmer I hardly notice it cold and like I said it goes away completely after warm up.
Burning Brakes
Joined: Sep 2008
Posts: 915
Likes: 31
From: Los Angeles CA
I am looking at buying black 2005 z51 which i took for a test drive on monday. The price is right, but the one thing i noticied was that when i got on the throttle in 3rd gear there was a litle bit of what sounded to me like an engine knock. There were no unusual sounds at idle or when driving casually around town.
The owner had the belt changed recently because he said that it had been squeaking. I pulled all of the codes on the car with my scan tool and found nothing current but a couple of old codes. one was for the MAF and the other was a body control system error.
Could this be the harmonic balancer issue or just low grade fuel? I wouldn't mind fixing the balancer, i'm just afraid it could be something worse. I also know i am really sensitive to sounds so maybe i am just making myself crazy
The owner had the belt changed recently because he said that it had been squeaking. I pulled all of the codes on the car with my scan tool and found nothing current but a couple of old codes. one was for the MAF and the other was a body control system error.
Could this be the harmonic balancer issue or just low grade fuel? I wouldn't mind fixing the balancer, i'm just afraid it could be something worse. I also know i am really sensitive to sounds so maybe i am just making myself crazy
I have the same exact issue as you precisely described on my 05 mn6 (non z51) I've had the car for about 3 years now and the knock under heavy accel. is bad at times and not as bad at times. I was leaning toward the gas we have in CA as the culprit but not too sure though. If I accelerate heavy but gradually the noise/knock is almost non exsistant but a heavy launch you can hear the knock. So I'm curious as well and also the car has been completely trouble free.
Thread Starter
Intermediate
Joined: Mar 2011
Posts: 39
Likes: 0
From: West Hartford CT
I have the same exact issue as you precisely described on my 05 mn6 (non z51) I've had the car for about 3 years now and the knock under heavy accel. is bad at times and not as bad at times. I was leaning toward the gas we have in CA as the culprit but not too sure though. If I accelerate heavy but gradually the noise/knock is almost non exsistant but a heavy launch you can hear the knock. So I'm curious as well and also the car has been completely trouble free.
Burning Brakes
Joined: Sep 2008
Posts: 915
Likes: 31
From: Los Angeles CA
It's been making the knocking noise since I bought the car. Obviously I didn't pick up the noise until after I bought it. It's not to a point where it concerns me either (well a little bit) but it hasn't got any worse and its ONLY under hard acceleration or a nice hard launch and it goes away. Keep in mind my car was/is in pristine condition as the previous owner took very well care of it and so do I. It actually has been an excellent car with no issues whatsoever other than the knock noise at times with hard acceleration. Like I said before, I suspect it may be the gas here. I've tried Shell, Chevron, 76, Valero, Mobil (all premium gasoline)and the knock seems worse with some of those brands. I get significantly less knock ONLY under hard acceleration using 76 and Shell with 76 knocking least. There has been quite a few threads in the past on here regarding engine knock upon acceleration or hard launches. When you search the threads you'll find them but there is nothing definite from those threads. Seems to be a common problem with certain cars and that's why I suspect the gas with all the additives we have here and emissions control.
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Thread Starter
Intermediate
Joined: Mar 2011
Posts: 39
Likes: 0
From: West Hartford CT
Thanks for the info!
I am thinking it may not be piston slap. Seems like piston slap is most noticable when the pistons have not come up to temp yet and is also noticable at idle. I am sure that the pistons would have had enough time to come up to temp.
or...... maybe the seller knew this and warmed it up before i got there? That's a scary thought.
I am thinking it may not be piston slap. Seems like piston slap is most noticable when the pistons have not come up to temp yet and is also noticable at idle. I am sure that the pistons would have had enough time to come up to temp.
or...... maybe the seller knew this and warmed it up before i got there? That's a scary thought.
