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I just got a my first corvette!!! Its a 1989 with 60k miles. It runs really well and is very responsive. under high rpms it seems to be making a rattling sound coming from the front half of the car. It sounds to me like detonation. It sometimes does it and sometimes does not. The trans shifts very well and the car sounds and runs as if it were times correctly.
there is also no loss of power under high rpms. Was curious if anyone has had this issue before, and has any ideas of what may be causing it.
I am unsure what is causing your noise. Perhaps you can give us some more information about when it does it.
Does it occur when the car is warmed up, or cold, or both? Do you notice any consistent conditions when it occurs or doesn't? Does it do it more in any particular gear? When it does it at that rpm is it at wide open throttle or does it occur at that rpm even if it is not wide open throttle?
What gas are you using? Have you had it long enough to know the gas wasn't sitting in the car for a long time while the previous owner had it. If you suspect detonation, make sure you have some fresh premium in the car of the highest octane you can find. I hope it is something as simple as gas, but in my experience I hear the most detonation at lower rpm under load so I am not sure it is detonation from your symptoms.
Good luck.
PS. We like pictures. Post some and show us your car and tell us about it.
Thank you so mucg for the response!! I'll make sure to post some pics at the end of this reply. I bought the car 4 days ago from a very nice older gentleman that only drove it on sundays. Other than the car was kept in the garage for 8 years. He was not much of a gear head from what I could tell, and I believe he just got standard oil changes as the air filter was rather fouled. The rattling only occurs during full throttle in drive when the temp is above 200. Does not make a sound at anything less than full throttle. It is very settle and equal in all gears. (it's an auto )- the previous owner told me he only used the highest grade fuel when he would fill up. And the gas tank was full when He sold it so it could be a possibility there is old fuel in the system. He also mentioned he rarely drove on the highway. I am replacing the cap rotor wires and plugs this weekend. It idles very smoothly however does seem to slightly shutter occasionally. I believe this will help, but if it doesn't what is the best way to clean the carbon deposites from the l98? Here she is! I stole this car for 4 grand. Automatic tan interior 60k miles. Overall very clean in and out
From your added descriptions, I would try driving a couple tanks of gas through it. That will make sure you have good premium gas. If it is detonation that you are hearing, you might take it easy on the potentially bad gas you have in it now.
If you are like me you will have a few times at WOT to help clear out possible carbon buildups. It sounds like the previous owner might not have driven it much or higher speeds, even perhaps not long enough to even get it warmed up good. You just don't know how it was treated or driven. I had one car that had sat almost undriven for years. After driving it for a few tanks of gas it noticeably ran better.
I don't know if that will cure your issues or not. Hopefully it will, but if not, at least you have a point to start from.
From what I'm reading, you just bought a car that has been sitting for a LONG time and are only now driving it and occasionally pushing the limits of the upper RPM band.
I'd drive it for a couple of weeks and make no changes but keeping notes about what concerns you. You first need to "baseline" your car before you start making adjustments, tuning or pronouncing things as problems. Simply, allow your car to "re awake" gently and then decide what you want.
As you mention, old fuel will make a big difference and can easily explain your pinging noise. If you give your car a tune up on old gas it will just run weird when you refill with fresh stuff.
So my .02 is go slowly and learn about your car before you make any changes. Trust me, in a short time there will be plenty to fix on your 28 year old car.
There are some gas additives that can aid in decarboning. Driving around in second in town and 3rd on the highway for a couple tanks can also a fun way to decarbon. When you can "punch it" to the floor and there's no big black cloud it should be good.
That's a good decision starting with a tuneup; cap, rotor, plugs and wires. The plugs will tell you if your car is detonating. As others have advised, get rid of the old gas before you start whomping on the thing. Good luck and congratulations.
I just got a my first corvette!!! Its a 1989 with 60k miles. It runs really well and is very responsive. under high rpms it seems to be making a rattling sound coming from the front half of the car. It sounds to me like detonation. It sometimes does it and sometimes does not. The trans shifts very well and the car sounds and runs as if it were times correctly.
there is also no loss of power under high rpms. Was curious if anyone has had this issue before, and has any ideas of what may be causing it.
Check what the ECM sees for detonation with a scanner. It should give you knock counts. If you want to, I'd suck all the gas out, dump a couple of gallons of fresh gas and drive to the gas station and fill up with premium gas. Make sure this is a shop with a huge patronage and not a Mom & Pop store out in the boonies. You can skip the snake oils that promise to remove carbon, clean valves, injectors, make the car fly, etc.
This is going to be dangerous but can you round up a friend to help you? Start engine and drive around to get it hot. Have him listen to the car while you press the brake pedal hard, put it in gear and give it a some gas to see if it does it under load and where it is from. I wouldn't do it for more than a few seconds.
Thanks to everyone for the replies. The love for the c4 is so awesome around here! I was at 1/8 of a tank and added some 93 oct from shell as well as some oct boost additive. I drove her around until I felt the gas was cycles. The next day I replaced cap and rotor ( electrodes looked a little corroded.) spark plugs wires, and o2 sensor since I found out there is only one. Just finished the tune and the thing is 1000% better. More responsive better idle and no detonation or knock under load. I will not be putting anything less than 93 in the future.
09-20-2017, 12:06 AM
rattling noise at 4500 rps
the previous owner told me he only used the highest grade fuel when he would fill up. And the gas tank was full when He sold it so it could be a possibility there is old fuel in the system. He also mentioned he rarely drove on the highway. I am replacing the cap rotor wires and plugs this weekend. It idles very smoothly however does seem to slightly shutter occasionally. I believe this will help, but if it doesn't what is the best way to clean the carbon deposites from the l98?
