Just got an 08 with the LS3 engine.

After driving it a thousand or so miles with absolutely no issues. I let it sit for about 10 days and when I first cranked it up, something was making a whapping noise under the hood. At first I thought it was a cat caught in the fan belt. But no cat parts were to be found. All engine gauges looked normal. Called my pro mechanic friend and he said it sounded like a tapping valve or stuck lifter. The more times I cranked it up and ran it briefly to try to figure out the problem, the less the sound got. So, since I still had the 5yr 100K warranty, I had it towed to the dealer. This Corvette has 20K miles on the clock. Dealer now has the heads off and checking for valve problems. I am waiting on a diagnosis.

Thought the LS3 was a great motor. My C5 LS1 was great. Is the LS3 a problem???? Is this a common problem???

 

Doesn't seem to be with the LS3. I've got one and I don't remember reading other posts about that problem here.

 

 

 

No, no common problems with the LS3. Frankly, I can't believe the dealer tore the engine apart so quickly. Makes me very curious. Please post back and let us know what happens.

 

heads off or valve covers off? I'd be surprised they tore it down so fast too.

 

Sound like a partially collasped lifter. When you ran it, it pumped up some but not all the way.

 

Sounds like lifters to me. Each time you started it, it was quieter. My guess is if you had driven it the noise would have disappeared. Mine will do that when the oil needs changing and after sitting for awhile.

 

Thanks for the feedback, I will give you an update when more is known. Good to know though the LS3 is a good motor, I like the 430hp!

 

I'm very interested in what the problem is here. My 2009 has had "noises" like rapping, tapping and such, similar to the "old" early LS1 piston slap, but definately NOT the piston slap my 98 did, but 3 dealers "can't duplicate" the problem. One local dealer even blamed a Texas dealer for doing an oil change!! The thing that upsets me with GM and the dealers is that with all the problems I've had with my 09 that required a test drive, trans-engine noise-GPS screen and more, they never took the car out. The car now has more the 36K on it and still the dealers don't "see" the problem...that attitude killed my purchase of a 2011 Vette.

 

Did you by any chance check your oil pressure? If the tapping went away when you drove the car, it could be that the pressure at idle is low, and went up to normal when the RPMs went up.

I say this because I recently bought an '08 from a private seller, and when we went to drive it, all was fine until we got back to his house and let it sit for a few minutes. When we started it again there was clearly lifter tapping noise. I checked the pressure and it was about 17PSI at idle, which concerned me because "typically" LS3 idle pressure is ~28 - 32. So we drove it to a local Chevy dealer, and the tech. said that 17PSI was fine, but they ended up replacing all the lifters under the 5/100 warranty anyway. So I bought the car.

Fast forward a few months....I really am going somewhere with this....

In the 105 degree heat this Texas summer I noticed that when the oil temp. went to 200+ degrees the idle pressure was now ~8 - 9PSI.. (which still meets the minimum GM specs BTW). It would always go to normal once you started to accelerate, and the RPMs went up.

Well doing some research here, I discovered that two, well actually three, things could cause this low pressure at idle. One is the bypass valve on the oil filter being stuck open. Replaced that, no help. The second is the oil pump itself. The bypass valve there can stick partially open, or open when hot, or an o-ring can get damaged during installation of the pump. I was able to convince a local Chevy dealer to replace the oil pump under the 5/100 warranty. The pressure at idle has been "typical" ever since.

FWIW, the tapping did not return after the original lifters were replaced, but I was still concerned about the idle pressure for longevity... So if you haven't already, check your oil pressure at Hot idle, once they finish with it...

 

Ok here is the update on the LS3. Hopefully this might help somebody.

Got the Corvette back yesterday and it runs great,

Here is some info:

* Oil pressure came right up about 40psig when I had the engine making noise initially. I will check it hot as suggested above.

*Dealer (which is knowledgeable and been around a long time, I have great experience with, so I assume they got it right) said the cause was: carbon on top of #2 piston and #2 exhaust valve so not sealing with carbon buildup.

*First after listening to the noise, they did a leak down test with 50% leakage and so pulled the right head to clean.

* Also found a miss when engine was loaded, discovered the bank 1 sensor 1 O2 sensor bad plus the right bank cat plug up.

Now, where and why the carbon buildup in #2, they do not know. I asked about bad gas, as my first guess, or oil leak?? or manuf defect or trash in engine or what??? I also asked if this episode might have damaged the cam, lifters ect and they did not think so.
they do not know. GM paid for all of this including the cat replacement and my Corvette runs great now, so I am happy. But, it would be nice to know the cause for certain.

On the post above with the 09, IMHO, I would do a leak down test first and see if you can get good results. You might get an independent or diy to get a 2nd opinion and then go to the dealer if bad.

Hope this helps and any feedback on causes including any WAG's are welcome! Thanks!!

 

Good Chance that bad gas caused the carbon build up. My E85 has my car sounding like a champ! Not much of a carbon issue with Ethanol

 

Sounds like a hung valve possibly caused by a bad valve seal ......could be but was it? I am surprised that the dealer could not tell you the cause. They fixed the symptom but if they did not fix the cause.........

 

Excellent point, they say the cause was carbon on top of #2 piston, but they do not know where the carbon came from for certain.

To determine the "root cause", you need to ask, why, why, why, otherwise you can do a fix that possibly does not solve the problem and "surprise" the problem returns! Hopefully this problem does not return and if it does, hopefully GM will pay for it again.

I have been using Citgo gas with no ethanol, since a tank sits for awhile sometimes due to not driving often and I wanted to avoid possible moisture separation. I normally use Chevron or Shell with detergent cleaners in the daily drivers. What gas do all of you use in your C6's???

Also, much thanks for the feedback and the info on the oil pressure problems causes!

 

seems to me if a sensor goes bad, there'll be incomplete burning which can cause carbon buildup. incomplete burning also dumps a lot of raw gas to cause a cat failure which then plugs up. and that can cause more things up the line it leads to. just guessing tho...glad it's fixed.

 

If it was running abnormally rich you could get carbon buildup which could mess with the valves ability to seal, further complicating the Air/Fuel mixture. Did they take a look at your intake to see how much oil was in there? If you have a lot of piston blow by, that could also explain the carbon buildup.

 

I did not get a check engine light, so no codes I think.

I thought if a sensor goes bad, it should kick out a code, but not necessarily?

Very educational, thanks!

 

Leaky injector?

I had a leaky injector on my 90' vette and it created alot of black soot on the plug. I'd imagine if it was doing the same to piston.

 

Who knows what kind of crap the previous owner was burning in your car.

Several years ago, before political issues, I asked a couple of respected local mechanics what gas i should run in my cars. One of them said "Any Top Tier brand, and definitely avoid Citgo." The other said simply "Not Citgo".

Some people say it's not a big deal, but my research has presuaded me that Top Tier gas will normally be better for the car over the long run.