Hot rod 90 vette
Melting Slicks
Joined: Nov 2007
Posts: 2,830
Likes: 147
From: Gainesville FL
Welcome to the forum
And maybe you can give us more to work with. There's a lot of things that can cause rattling on acceleration. Motor mounts? Rocker arms out of adjustment? Broken pre-cats?
Last edited by 3D-Aircrew; Oct 16, 2018 at 04:01 PM.
Safety Car
Joined: May 2001
Posts: 4,759
Likes: 1,647
From: Fairfax Virginia
Welcome to the Corvette Forum RodneyRutherford!!
The guys that responded are correct, we need to know more about the conditions in which you hear the rattling. What brand and Octane of gas you use and whether you have done any modifications to the car? Did any previous owners do anything to the car like modifications?
"Rattling" in a car is a very general term. When does it happen? Is it under a load when the rattling starts or does it rattle all the time when running? The other question for you is where does the rattling sound come from? The engine? The middle of the car? The rear of the car?
Is this your first Corvette? Do you have a set of the Factory Service Manuals (FSM's) for your particular year? If not then order them as soon as you can. They are priceless when you work on one of these cars.
You did mention that under "High (Hard?) Acceleration it starts rattling" and that would likely be "detonation" from what I would guess. But it could be a bad rocker arm or a bunch of things under the hood. I would bet you are talking about detonation which happens on engines running with lower octane than the engine requires. How many miles are on the engine? Older engines get carbon and other cylinder build-ups that can cause Pre-ignition which sounds like detonation or rattling.
I would start by getting a bottle of BG 44K Fuel System Treatment from a local auto parts store or you can order it from Amazon as well. BG 44k is used to clean the entire fuel system pretty thoroughly and is used daily by thousands of mechanics. It is not cheap but it WORKS really well, do not substitute other brands as I can't attest to whether it works or not. I KNOW the BG 44k works. The other thing is to use better gasoline until you get this resolved, the higher the octane the SLOWER it burns so it should slow down or stop your issue of the "Rattling L98". Try using the Sunoco 93 octane gasoline and see if your Corvette is happier on it
I would suggest that you check your timing on your engine, if the timing is too advanced it will make the engine detonate. On my 1988 C4 with the L98 it is set at 6* but a lot of folks like to set it at 8* and that simply requires that you have to use premium fuel.
If the rattling sound is happening all the time when the engine is running and you hear the sound coming from below the center area of the car then you MIGHT have a broken Catalytic Converter. It is fairly easy to check, you just get down on your knees and listen on each side to identify the location of the offending sounds. The 1988 C4 has three catalytic converters, two pre-cats on the pipes that connect to the exhaust manifold and a Main catalytic under the passengers seat area. Yesterday there was a member trying to resolve a rattling catalytic converter. I leave the catalytic converters where they are as they are required by Federal law, now if one is shaking and rattling you can either replace the catalytic (With an aftermarket HI-Flow) or eliminate the internal ceramic parts from the converter shell. It is very easy but highly illegal to do on any car used on Federal Highways. To get home one time I emptied out the catalytic converter by using a long screwdriver and a hammer. One good whack and the millions little parts fell right out leaving a hollow shell, and then you put the shell back on the car and you are set to go. This solution is only being suggested as a "temporary solution" until a proper Converter can be re-installed. I am a strong believer in keeping our emissions equipment functioning as long as I own and drive the car.
There are so many parts that will make a rattling sound if not tight or broken, I listed off a couple thoughts but we really need to know more information to really help you narrow down the search for your rattle.
I had a clicking sound on a freshly rebuilt engine that got progressively worse and it turned out that one of my push-rods oil passageway was blocked off and that caused the roller rocker arm to fail and the clicking got louder and louder until I got home and solved it. I thought I had flushed them out when cleaning them prior to installation but one got by me somehow.
So in summary I would just sit down and tell us all you know about this issue and your particular car. Has it done it since you bought it or did it just start out of the blue? Order the FSM for your car so you will be able to work and understand the car better, again, only the factory service manual is worth having, don't waste your time with the others like Chiltons or Clymers.
Once again Welcome to the Corvette Forum, this site is a true asset for anybody who owns a Corvette! Get us the additional information and we can help you more completely!
Best Regards!
The guys that responded are correct, we need to know more about the conditions in which you hear the rattling. What brand and Octane of gas you use and whether you have done any modifications to the car? Did any previous owners do anything to the car like modifications?
"Rattling" in a car is a very general term. When does it happen? Is it under a load when the rattling starts or does it rattle all the time when running? The other question for you is where does the rattling sound come from? The engine? The middle of the car? The rear of the car?
Is this your first Corvette? Do you have a set of the Factory Service Manuals (FSM's) for your particular year? If not then order them as soon as you can. They are priceless when you work on one of these cars.
You did mention that under "High (Hard?) Acceleration it starts rattling" and that would likely be "detonation" from what I would guess. But it could be a bad rocker arm or a bunch of things under the hood. I would bet you are talking about detonation which happens on engines running with lower octane than the engine requires. How many miles are on the engine? Older engines get carbon and other cylinder build-ups that can cause Pre-ignition which sounds like detonation or rattling.
I would start by getting a bottle of BG 44K Fuel System Treatment from a local auto parts store or you can order it from Amazon as well. BG 44k is used to clean the entire fuel system pretty thoroughly and is used daily by thousands of mechanics. It is not cheap but it WORKS really well, do not substitute other brands as I can't attest to whether it works or not. I KNOW the BG 44k works. The other thing is to use better gasoline until you get this resolved, the higher the octane the SLOWER it burns so it should slow down or stop your issue of the "Rattling L98". Try using the Sunoco 93 octane gasoline and see if your Corvette is happier on it
I would suggest that you check your timing on your engine, if the timing is too advanced it will make the engine detonate. On my 1988 C4 with the L98 it is set at 6* but a lot of folks like to set it at 8* and that simply requires that you have to use premium fuel.
If the rattling sound is happening all the time when the engine is running and you hear the sound coming from below the center area of the car then you MIGHT have a broken Catalytic Converter. It is fairly easy to check, you just get down on your knees and listen on each side to identify the location of the offending sounds. The 1988 C4 has three catalytic converters, two pre-cats on the pipes that connect to the exhaust manifold and a Main catalytic under the passengers seat area. Yesterday there was a member trying to resolve a rattling catalytic converter. I leave the catalytic converters where they are as they are required by Federal law, now if one is shaking and rattling you can either replace the catalytic (With an aftermarket HI-Flow) or eliminate the internal ceramic parts from the converter shell. It is very easy but highly illegal to do on any car used on Federal Highways. To get home one time I emptied out the catalytic converter by using a long screwdriver and a hammer. One good whack and the millions little parts fell right out leaving a hollow shell, and then you put the shell back on the car and you are set to go. This solution is only being suggested as a "temporary solution" until a proper Converter can be re-installed. I am a strong believer in keeping our emissions equipment functioning as long as I own and drive the car.
There are so many parts that will make a rattling sound if not tight or broken, I listed off a couple thoughts but we really need to know more information to really help you narrow down the search for your rattle.
I had a clicking sound on a freshly rebuilt engine that got progressively worse and it turned out that one of my push-rods oil passageway was blocked off and that caused the roller rocker arm to fail and the clicking got louder and louder until I got home and solved it. I thought I had flushed them out when cleaning them prior to installation but one got by me somehow.
So in summary I would just sit down and tell us all you know about this issue and your particular car. Has it done it since you bought it or did it just start out of the blue? Order the FSM for your car so you will be able to work and understand the car better, again, only the factory service manual is worth having, don't waste your time with the others like Chiltons or Clymers.
Once again Welcome to the Corvette Forum, this site is a true asset for anybody who owns a Corvette! Get us the additional information and we can help you more completely!
Best Regards!
Advanced
Joined: Oct 2017
Posts: 53
Likes: 4
From: Farmville Virginia
If by "high acceleration" you mean when you accelerate hard I had the same problem. Mine turned out to be in the timing. Made a slight timing adjustment and the rattle went away and picked up a little power too!
