The GM Service Writer says the knocking noise is normal. NORMAL? I'm having a hard time letting this go. My warranty is up in August! I really could use some expert advise from you seasoned vets out there.

I've wanted a Vette ever since my first muscle car back in the early seventies but could never afford one. Had to settle for what was affordable. Drove my first C5 a few years back, Loved it, so my wife and I found a way to Finally afford an 2003 Corvette. Ok, enough of the cry baby stuff.

Now you can imagine my disappointment. We hardly drive this car much. Only has 7500 miles on it. I love this car but I'm actually considering selling when I really don't want to.

The knocking lasts (at idle or high idle) as far as driving to the grocery store about a mile and a quarter away! When the motor is at idle before I shut it off, it still sounds the same. After driving for a few miles you can't hear the knocking anymore. Get this, what's really strange is after the hot engine is shut off for a half hour/45 minutes, anywhere up to 2-3 hours, then restart it , the knocking is louder!

I've read about new engines with piston slap. Someone on the forum mentioned something about knocking was a result of an oil pump O-ring??

I really could use some expert advise from you seasoned Corvette owners out there.

I think this should be a warranty issue. I can't believe this is normal .

 

It's always good now a days to get a second opinion. Take it to another shop and ask them what they think is the problem , then you can figure it out. Have them give it to you in writing, that is my .02

 

I would bring it to a Vette tuner and have them inspect it.
Good luck!

-Mike

 

I don't have a solution, only wanted to say I feel very bad about your situation. Something doesn't sound kosher to me... not "normal" that it's knocking. Someone else, aside from someone with a vested interest (like the dealer), needs to assess the problem.

 

Sounds like piston slap.. And if you gain an understanding at to why it's happening, maybe it can help you relax and enjoy the car..

It knocks when cold because the high-performance pistons haven't come up to temp yet, i.e. the haven't expanded to thier final dimention..

So think about that above sentence; they could make the pistons larger, or the bores tighter, but that could a: rob horsepower, or b: cause excessive wear when up to temp and running hard.

These motors (compared to the competition anyway) are making decent power, still meet emissions and get good gas mileage as well.

Try to think of this "issue" as a trade-off for having a car that kicks *** once it's warmed up. Hope that helps.

 

Bob, this noise is not normal. Go to several GM dealers for evaluation and get their rsponse in writing via the service report. Are you getting any PCM codes?

The following info was found at this link. http://www.motorage.com/motorage/art...l.jsp?id=54994

2001-03 Corvette, Camaro/Firebird, C/K Trucks with V8 engine
Engine knocking that sounds like a collapsed lifter may be caused by a cut O-ring in the oil pump. The noise will be noticed when the car (or engine) is brand new and may be heard when the engine is cold, seem to diminish, then return as the engine warms up. The O-ring seal between the oil pump and the pick-up screen may be cut, causing aeration of the oil. The bulletin lists part numbers but no repair instructions.
Bulletin 02-06-01-038

Here's another link to look at.
http://www.rjsmith.com/gm-1206539.html

I would advise getting an extended warranty. Fitchner has very good prices.

 

Hi Bob,

I have the exact same issue with my 2002 with 12k miles. I was concerned about the TSB concerning the oil pump cut "O"-ring and took it to the dealer to make sure my concerns were documented, just to be safe. I also ensured the dealer referenced the TSB on my work order for "CYA" in case the "O"-ring turns out to be the cause (my warranty expires in Apr 06). However, I agree with the dealer and believe it is piston slap. Mine too sounds worse after the car sits for an hour or two and then is restarted. My novice guess is that the pistons cool faster than the cylinders, aggravating the "slap". However, when fully warmed she screams like a banshee! I love the car and it is just something I will live with. Also, my Borla exhaust hides most of the "slap" anyway.

I don't feel it's the "O"-ring because oil aeration (fancy word for oil foaming) should most likely result in noise even after the egine reaches normal operating temp. I would recommend a warranty visit to the dealer to make sure this is documented. Make sure he references the TSB on the work order and if he says it's engine knock make sure he states on the work order that the noise is not being caused by the cut "O"-ring. If he's wrong, this will give you legal recourse even after the basic warranty is expired. Also, ditto on purchasing an extended warranty.

If you are not already aware, head for http://www.corvetteactioncenter.com/...dgebase/browse categories/1997 - 2004 corvettes/engine - mechanical for a list of all TSBs, including the oil pump.

My final advise is relax and enjoy the 'vette. It's an american car so it's going to have some engineering issues!

 

My advice is to take it to another dealer preferably with some very good Vette Tech's. Maybe some other members will chime in and advise where in AZ to take the car to be diagnosed.

 

You have piston slap as Dan mentioned. This is a very common problem with the LS1. I've just learned to live with it. Check out this web site www.pistonslap.com

 

I looked at the web site you posted. Sounds like a VERY severe problem that needs to be repaired under warranty. If I was to buy your car I would deduct price of an engine from my offer just in case.

 

Piston slap for a mile and a half? sounds a bit much... my car has 78k miles on it. it makes a very little noise for bout 20 seconds then quiets right down...

I would take that car to a few places and get it really checked out before that warrenty is up

 

Guys, Thanks for all the good advise and tips. I really appreciate your input!

To Dan the C5 man - Yes, I agree, these cars do run well!

To Korreck, Bob - No PCM codes. Thanks for the links, interesting!

To decoffee - Sorry to hear that you have possibly the same problem I do. I've got to admit that your story makes me feel like I'm not alone going nuts with this knocking issue. Interesting that yours too is louder after restarting a warm motor. Your idea makes sense, cooler pistons with warmer cylinders. I was thinking along the same lines too. But at the same time it's also hard to imagine that there would be that much of a temp. variance within different parts inside a sealed motor to make the clearances that much greater resulting in a louder knocking. Crazy!
PS - For some reason I couldn't open that link. I'll try later...

Thanks Guys...

 

David, thanks. I've been to this site before. This site is scary. When they all start mentioning attorneys and class action law suits, well, I prefer not to go there. Maybe after about 10 years we all end up with a check for a 100. bucks towards new pistons and a do-it-your self instruction booklet and the attorneys make millions.

 

I think it's a bit much too. I do have a 160 t-stat but it is HOT out here too. The 160 might prolong the knocking sound???

 

If the noise your hearing is happening at start up and at idle then you aren't pinging. A couple things to check. First off you may have an actual case of piston slap. Dealers usually won't do anything for it. But if you get in their face enough you might get one to retrofit the pistons for you. Good luck there. Another thing that I have found in my LS1 adventures is a bent push rod or loose rocker due to the needle bearings falling out. Have you over revved this pig, missed a gear shifting? Don't be shy, tell the truth. If it is piston slap then you have a couple of choices. First off ignore it, drive the **** out of it and have fun driving with the radio turned up loud. Second, you can take it to a good LS1 speed shop and let them tear it down and retro fit the rings and double check the push rods and rockers. That will fix piston slap.

If you think you have actual pinging then the first thing you need to do is find someone that has a scanner that will monitor your knock sensors to see of what your hearing is really knock. If it is knock the first thing you need to do is a top end cleaning. I would also do an injector flush and change plugs to one level cooler plug. I noticed that you in AZ, freaking hotter than the face of the sun area. I would have a tuner check your AF ratio. I find that the cars PCM tends to run a little on the lean side so richening it up through the power band a bit will not only yield more power the extra gas acts as a cooling agent and keeps true pining down. Put in a 170 stat and have your tuner turn on the fans earlier so as to keep the engine about 10 degrees cooler. Next I would add "Water Wetter". This stuff is magic in how it helps the efficiency of the cooling system. My suspicion is your running hot which will cause pinging at even the lowest speeds and load.

I kind of doubt that you have pinging since you said you only have 7K on the car.

 

No, never been over revved w/a missed gear. This is an A4 car. I have hit the rev limiter twice shifting manually since I've owned it. The car runs better shifting by itself. I rarely push the car that hard anyway. I've Never even done a burnout with this thing. So abuse is a non-issue here.
AF has been checked by Xtreme Motosports at about 4500 miles. Also has a 160 stat w/ fans reprogramed starting up about 192-194 degrees. Otherwise the engine is stock and doesn't leak or burn a drop of oil.

This might be interesting: One time, a few thousand miles back, when I started the car after a (approx.) 5 week sit, It made a helluva valve train bang noise. My Wife, not knowing much about cars except put gas in and go, said "WHAT WAS THAT!". In short I replied way too dry lifters(or so I thought).
Possible a bent push rod?
The knocking noise appears deeper than up top and on the drivers side. But that might not mean anything either as we all know how sound can travel.
Ugh!

 

You've gotten a lot of good advice, especially from me. Now is the time to take action to protect yourself. Good luck and let us know how you came out with this problem,

 

Thinking about a bent pushrod, screwedup lifter or rocker. I would think these would make noise all the time.
When the engine is well warmed up, it sounds nice and normal.

Maybe I'll just wait until August when the new LS7 crate motors are available!!!

 

Exactly.. You can try to "force" this issue with your dealer.. And if you search here you can find all sorts of horror stories of dealers screwing up cars worse than when they came in.. If it was my car, I'd leave it alone. The only thing I'm worried about at this point is if the world explodes and Korreck is the only one left w/ any money to buy my car.. Uh boy, I'm going to take a bath on that deal!

 

I just got back from Extreme Motorsports. Mike assures me that my knocking is pretty common with these LS1's. Like alot of you said, just run it! It's just way it is.

We both agreed that we would not want a GM dealer installing new pistons even if they begged me to do it. That would just be asking for more problems.

I think I'll proceed with the mods I was planning.

Thanks for your input guys!

PS - I wouldn't mind if Dave Hill read this, called me up, and asked me if I would be kind enough to accept one of his new LS7 crate engines for my coupe.... Dave, are you listening ?!?!?!