strange sound under acceleration...?
Thread Starter
Racer
Joined: Feb 2007
Posts: 284
Likes: 30
From: Gordon Nebraska
strange sound under acceleration...?
Okay if I am crusing along in say in 5th or 6th gear, pulling low rpms/lower speed, and I accelerate with out down shifting I can hear what I can best describe as what sounds like a diesel engine sound coming from the engine area. Kinda of a clicking,knocking, just overall strange sound at least to me. This is on a 2001 Z06 by the way. Just wondering if anyone knew what it was or could be, I know this is pretty general, so hopefully someone can help me shed some light on it.
Jon
Jon
Tech Contributor
Joined: May 2008
Posts: 2,843
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From: Howell Michigan
St. Jude Donor '09-'10-'11
Jon,
You maybe getting into spark knock, but you really don't want the engine rpm below 1500 while stepping into it. Down shift. If it happens above 1500 rpm and with light step-in you might have a knock sensor issue. Have you checked the DIC for codes? Might want to take a look. I'm sure your using premium fuel too.....right?
Eric D
Last edited by Eric D; Jun 23, 2008 at 12:14 PM.
Thread Starter
Racer
Joined: Feb 2007
Posts: 284
Likes: 30
From: Gordon Nebraska
Yes premium fuel is being used, typical example would be hiway driving, someone slows down slightly in front of me and I let off the gas and then once they are out of the way I just reapply the accelerator, car accelerates, but noise is present, not talking about super low speeds but around 50-60 in 6th I would say. Easiest way to describe would be having the car under load, say going up hill in to tall of a gear, car will accelerate out of it, but should probably down shift "lazy and cruise is set" If its just a matter of making sure I always down shift then that is no problem, but if I need to get some sea foam and blow the carbon outa this thing as well I will. Another problem may be that the only 91 octane gas that I have available is an ethanol blend, everything else is 89 or less with 91 being the highest available in a 150 mile radius. Should I fill up with 89 being its pure and add octane booster? Thanks in advance.
Tech Contributor
Joined: May 2008
Posts: 2,843
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From: Howell Michigan
St. Jude Donor '09-'10-'11
Jon,
IMHO 50 - 60 mph you should downshift to 5th. 6th gear at 55 and below the engine rpm is below 1500. You want to downshift to keep out of spark knock and to keep enough oil flow to the bearings under this type of load for cooling. There is some risk of spinning a main or rod bearing if this is done in excess. As far as the fuel, some states all you can get is ethanol blend to 10%. The engine is designed to handle this amount. I wouldn't worry too much about using it. Though I was a skeptic at first, I'm a believer in using Techron in my fuel tank at every oil change. The stuff really works. If you haven't used it before do a search here on it.
Regards,
Eric D
IMHO 50 - 60 mph you should downshift to 5th. 6th gear at 55 and below the engine rpm is below 1500. You want to downshift to keep out of spark knock and to keep enough oil flow to the bearings under this type of load for cooling. There is some risk of spinning a main or rod bearing if this is done in excess. As far as the fuel, some states all you can get is ethanol blend to 10%. The engine is designed to handle this amount. I wouldn't worry too much about using it. Though I was a skeptic at first, I'm a believer in using Techron in my fuel tank at every oil change. The stuff really works. If you haven't used it before do a search here on it.
Regards,
Eric D
Last edited by Eric D; Jun 23, 2008 at 10:13 PM.
Pro
Joined: Mar 2006
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When my C5 was stock I avoided being in 6th gear below 65mph. Others may disagree, but I always felt I was lugging the engine in 6th below 65. You're really not gaining any gas mileage by riding in 6th below 1500 either. Gas may not be cheap anymore, but engine repairs cost even more.
Thread Starter
Racer
Joined: Feb 2007
Posts: 284
Likes: 30
From: Gordon Nebraska
Alright thanks guys, I will just bite the bullet and downshift the beast when I should and if it gets worse and it should go away, if it comes back at a later date I will be back!! hehe. Thanks again.
Jon
Jon
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Safety Car
Joined: Sep 2001
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From: Cumming Ga
Hi Jon,
It is not the car, nor the gas...the car is not designed to accelerate in 6th gear at such low speeds. The engine does not have enough torque. Part throttle acceleration is ok, but full throttle does not make sense- it is always better to downshift to at least 5th. It's kind of like starting out at a stop sign in 4th gear, and wondering why the car is bucking.
Tim
It is not the car, nor the gas...the car is not designed to accelerate in 6th gear at such low speeds. The engine does not have enough torque. Part throttle acceleration is ok, but full throttle does not make sense- it is always better to downshift to at least 5th. It's kind of like starting out at a stop sign in 4th gear, and wondering why the car is bucking.
Tim
Thread Starter
Racer
Joined: Feb 2007
Posts: 284
Likes: 30
From: Gordon Nebraska
I am not mashing the accelerator, it is just a "regular" accleration, but I am sure it is still the same problem, too tall of a gear demanding too much out of it. Down shifting will more then likely solve all my woes. Thanks Tim for the input, I figured it wasn't the car, and it was "me". Just need to modify my driving behavior.
Jon
Jon
Instructor
Joined: Sep 2006
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From: lockport IL
i also have a similar problem, i have a heavily modded vert and when the converter locks up at 40 mph and i accelerate it sounds like there is a rattle in the front of the car. it only does it after the converter is locked up and under light acceleration. 
any ideas?
any ideas?
Tech Contributor
Joined: May 2008
Posts: 2,843
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From: Howell Michigan
St. Jude Donor '09-'10-'11
What rpm is the engine at when the rattle occurs? If you take the rpm higher does the rattle go away?
Analyzing noises from the web using someone’s written description obviously leaves a high chance of error in the guess of the source. Some of the more likely sources are spark knock, torsional vibration of the prop shaft, something on the exhaust system rattling or contacting frame or other parts, etc… Knowing the engine rpm when the noise occurs is one of the better clues.
Eric D
Analyzing noises from the web using someone’s written description obviously leaves a high chance of error in the guess of the source. Some of the more likely sources are spark knock, torsional vibration of the prop shaft, something on the exhaust system rattling or contacting frame or other parts, etc… Knowing the engine rpm when the noise occurs is one of the better clues.
Eric D
Instructor
Joined: Sep 2006
Posts: 162
Likes: 0
From: lockport IL
What rpm is the engine at when the rattle occurs? If you take the rpm higher does the rattle go away?
Analyzing noises from the web using someone’s written description obviously leaves a high chance of error in the guess of the source. Some of the more likely sources are spark knock, torsional vibration of the prop shaft, something on the exhaust system rattling or contacting frame or other parts, etc… Knowing the engine rpm when the noise occurs is one of the better clues.
Eric D
Analyzing noises from the web using someone’s written description obviously leaves a high chance of error in the guess of the source. Some of the more likely sources are spark knock, torsional vibration of the prop shaft, something on the exhaust system rattling or contacting frame or other parts, etc… Knowing the engine rpm when the noise occurs is one of the better clues.
Eric D
Drifting
Joined: May 2008
Posts: 1,490
Likes: 17
From: Oakville, Ontario
that brings up an interesting question? I too fell that 6th gear at under 65 is not good, but having said that, is there a rule of thumb for speed vs 6th gear when in cruise control mode? When I'm in the USA on the Interstate, generally 72-74 mph in cruise, I'm at 1400-1500 rpm, feels great...any thoughts?
Le Mans Master
Joined: Oct 2005
Posts: 7,088
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From: Metro Detroit Michigan
Geez guys, engine management should handle full throttle without pinging at any rpm.
"Lugging" is kind of an archaic concept. The Corvette was set up to handle the 1-4 "skipshift", which puts rpms in the basement under acceleration, so why shouldn't he expect to be able to accelerate in 6th from 50 mph?
Something's not right with the car. Problem isn't with the driver.
My supercharged Corvette doesn't ping even if I floor it at 400 rpm.
"Lugging" is kind of an archaic concept. The Corvette was set up to handle the 1-4 "skipshift", which puts rpms in the basement under acceleration, so why shouldn't he expect to be able to accelerate in 6th from 50 mph?
Something's not right with the car. Problem isn't with the driver.
My supercharged Corvette doesn't ping even if I floor it at 400 rpm.
Last edited by Warp Factor; Jun 24, 2008 at 09:14 PM.
Tech Contributor
Joined: May 2008
Posts: 2,843
Likes: 16
From: Howell Michigan
St. Jude Donor '09-'10-'11
Geez guys, engine management should handle full throttle without pinging at any rpm.
"Lugging" is kind of an archaic concept. The Corvette was set up to handle the 1-4 "skipshift", which puts rpms in the basement under acceleration, so why shouldn't he expect to be able to accelerate in 6th from 50 mph?
Something's not right with the car. Problem isn't with the driver.
My supercharged Corvette doesn't ping even if I floor it at 400 rpm.
"Lugging" is kind of an archaic concept. The Corvette was set up to handle the 1-4 "skipshift", which puts rpms in the basement under acceleration, so why shouldn't he expect to be able to accelerate in 6th from 50 mph?
Something's not right with the car. Problem isn't with the driver.
My supercharged Corvette doesn't ping even if I floor it at 400 rpm.
The bottom line, it's your car, you can drive it as you see fit. As far as the 1-4 “skipshift”, this was government intervention at its finest. No engineer would do this on their own, it's a bad idea,
but it was necessary to meet a government mandate, not because some engineer thought it was a cool feature for a sports car! As far as cursing on fairly flat terrain at 70+, 6th gear is fine, in fact I run there frequently when going some place of distance. When I need to excel it gets dropped to the gear that will get the engine above 1500 rpm.
As far as your supercharged Corvette not ping, you or someone most likely spent a fair amount of time tuning it to keep it out of detonation, not to mention you are most likely running lower compression to help control it compared to a normally aspirated engine.
Eric D
Intermediate
Joined: Jun 2008
Posts: 35
Likes: 1
Wrap Factor,
The bottom line, it's your car, you can drive it as you see fit. As far as the 1-4 “skipshift”, this was government intervention at its finest. No engineer would do this on their own, it's a bad idea, but it was necessary to meet a government mandate, not because some engineer thought it was a cool feature for a sports car!...
The bottom line, it's your car, you can drive it as you see fit. As far as the 1-4 “skipshift”, this was government intervention at its finest. No engineer would do this on their own, it's a bad idea,
but it was necessary to meet a government mandate, not because some engineer thought it was a cool feature for a sports car!... 
Instructor
Joined: Sep 2006
Posts: 162
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From: lockport IL