Z06: Knock, knock.
Me: Who's there?
Z06: Detonation.
Me: Oh, s#&@.
Two days after he picked up our longterm 2002 Corvette Z06, Senior Editor Ed Hellwig thought he heard engine knock at full throttle around 4000 rpm. I took it for a drive and confirmed that, sure enough, it was definitely detonation Ed was hearing.
The previous owner didn't pile on the miles. We figured maybe the fuel in the tank was old and had become octane-deficient. So we ran three tankfuls of fresh 91 octane through it. It made no difference -- the Z06 still pinged like crazy.
We brought it to the dealer last week to have them check into it. They reflashed the ECU with an updated calibration and separated us from $98. Again, no difference.
At this point we thought maybe we were nuts. To be doubly sure that what we were hearing was in fact detonation and not something mechanical in nature, we added octane. Yesterday I mixed five gallons of 100 octane with the few remaining gallons of 91 still in the tank. The pinging vanished.
We'll bring it back it back to service once all the 100 octane fuel has been replaced with 91. Maybe this time they'll check the timing and verify that the knock sensor(s) haven't crapped out.
It's anyone's guess as to how long the engine has been running in this state. Though it runs strong according to the ol' butt dyno, a basic compression and leakdown test would be a good first step in determining whether prolonged detonation has caused any engine damage.
Jason Kavanagh, Engineering Editor @ 42,340 miles.
hondacura4 says:
12:38 PM, 01/19/10
Detonation is N E V E R a good thing. I've ran across a few cheap asses who put mid-grade fuel in their S2000's and wonder why performance and fuel economy have diminished so much. I always tell hem that PREMIUM fuel is a REQUIREMENT for this car and they still don't get it or simply make excuses. Why spend this kind of money on any car yet put the equivalent of mule piss in it?
compliance says:
12:42 PM, 01/19/10
check the plugs?
jasond52 says:
12:42 PM, 01/19/10
Was the knocking noticed on the test drive before the car was bought? Surely it was taken over 4 grand on that drive...
benson2175 says:
12:56 PM, 01/19/10
I foresee complicated and expensive repairs in your future. Sell the car quick.
sodaguy says:
01:19 PM, 01/19/10
Sometimes, pinging can be the result of heavy carbon build-up on the tops of the pistons.
An inexpensive solution that you can try is to add one bottle of highly-concentrated fuel system cleaner such as Amsoil PI or Redline SI-1 to an empty tank prior to fill-up. In addition, introducing a cleaner such as Seafoam or Amsoil PowerFoam through the throttle body will also help clean the top end of the engine. Those two things combined may help the situation.
Instead of doing this yourself, you can have your dealer perform a fuel induction service, which is basically the same thing. These services are performed with chemicals supplied by vendors such as BG and Wynn's. They include adding a strong cleaner to the fuel, cleaning the top-end of the engine with a Seafoam-like chemical, and cleaning the throttle body. The cost is around $150 and may be worth a try.
ptcdawg says:
01:26 PM, 01/19/10
I tend to agree with Sodaguy....
Why no 93 octane? That what we sell here in God's Country....
sodaguy says:
01:37 PM, 01/19/10
@ptcdawg: Unfortunately, 93 octane is not available in CA. :(
desmolicious says:
01:44 PM, 01/19/10
What sodaguy said. Run a tank of fuel with seafoam in it through it.
See what happens.
bodyblue says:
02:02 PM, 01/19/10
What Benson said......GET RID OF IT.....and you guys thought the Ferrari was expensive to maintain.
mrryte says:
02:07 PM, 01/19/10
sodaguy says:
"@ptcdawg: Unfortunately, 93 octane is not available in CA. :( "
This truly baffles me. What possible reason could Cali have for not offering anything over 91 octane???
jeepsrt says:
02:12 PM, 01/19/10
Try a can of BG 44K, we use to put that in my Wifes Prelude in high school worked great.
matt310 says:
02:17 PM, 01/19/10
Blame the CARB (California Air Resources Board) for the evaporation of 93 octane back in the summer of 2001. That 76 station in the photo is at Pico and Bundy in West LA and the price for a gallon of 100 is $9.49. I sometimes have to add some to my RS4 to keep it from pinging, too. It's the price you pay for high-performance, and the engine in my car and the Vette's are worlds apart in design, yet they still behave exactly the same way with crap gas.
dougnash2009 says:
02:26 PM, 01/19/10
It's a joke. California has the most cars, yet has the lousiest choice in fuel. Plus, with such a trend-setting environmental stance, one would think that higher-octane fuel would be available here. Even though it doesn't directly lead to better economy, it certainly allows any motor to operate at its most efficient timing.
estreka says:
02:53 PM, 01/19/10
It's not just CA. Most western states only get 91 octane. It's really annoying when you have a car that needs 93 octane. My car would backfire sometimes when I let off the throttle. One reason I'm glad I left Montana. ;-)
fuhteng says:
02:58 PM, 01/19/10
estreka - what the heck were you driving? I have 91 in Kansas. Happily my small-block Chevy doesn't mind (but no, I don't put regular in it). It seems to me that if this is really such an issue, you all need to have your engines detuned (computer work for everyone I assume) so you don't hurt it.
bodyblue says:
03:59 PM, 01/19/10
I just thought of something....did you test drive the car before you paid for it?? And if you did, did it ping? And if you did test drive it, did you not give it full throttle?
dougnash2009 says:
04:07 PM, 01/19/10
Engines in vehicles destined for California ARE de-tuned. Well, more accurately, they're re-flashed for lower octane. It still doesn't always help, and the turbo cars are hurt the most. In the summer, when really jumping on the throttle, you can still here some occasional pinging. Really comforting.
subytrojan says:
04:44 PM, 01/19/10
D'oh! What's the best long-term solution, folks? My WRX has an occasional ping at WOT, too. It always worries me. I had it Protuned in January 2008 by HB Speed in Fountain Valley to run safer than the AccessPORT off-the-shelf stage 1 91 octane map.
hybris says:
05:44 PM, 01/19/10
Hmmm the only solution to this I can see is to move Edmunds.com from anti-car state of Califorina and move them to Kansas were 93 octane is plentiful and every day the weather is a challenge unto its self.
subytrojan says:
05:58 PM, 01/19/10
Or just bring us a bunch of your good gas, hybris!
subytrojan says:
05:59 PM, 01/19/10
What Audi is that in the background, Jay? RS 4? :)
roadburner says:
06:02 PM, 01/19/10
It's the IL gas; it hates GM cars...
vt8919 says:
06:32 PM, 01/19/10
Add to the graffiti on the pump the following:
"Here I stand, broken hearted,
Buying 100 cuz' knocking started."
greenpony says:
06:57 PM, 01/19/10
And so it begins.
spdracerut says:
07:03 PM, 01/19/10
I'm thinking along the lines of carbon buildup also. Seems to me the car was a weekend cruiser. I say.... head to the road course, dump in some 100 oct with the 91 oct, and drive the piss out of it to get rid of the carbon :)
vt8919 says:
07:09 PM, 01/19/10
If the engine blows up I wanna see a YouTube video. Have Donna narrate it.
slickersdrip says:
07:37 PM, 01/19/10
My dad's right now trying to decide between a 2003-5 Z06 or a 2011 Mustang GT, so I'm loving this posts about this car.
Here in the great state of Texas we have the best gas possible... please open up an office here in Austin. We have great driving roads, average to minimal traffic and the best culture possible. Perfect place. Plus, I'll throw in the first few gallons of 100 octane gasoline to see an office here.
slickersdrip says:
07:42 PM, 01/19/10
...these, not this... please, with all of the "upgrades" of this blog can we please get the editing system back?
stovt001 says:
08:10 PM, 01/19/10
I think it is more than a bit silly to predict at this stage that this car will be particularly expensive to maintain. Parts are not exactly hard to find and there is nothing really exotic involved.
I do agree with the moving out of California sentiments. The only factors keeping me here are my wife's student loans (half will be forgiven if she teaches in the state for so many years) and my dream to one day work for Edmunds.
bimmerjay says:
09:01 PM, 01/19/10
Loose pushrods? Creaky leaf springs? Heh
church123 says:
10:03 PM, 01/19/10
JK, one thing to keep an eye on is which gasoline brand you're using (91 that is). One advantage of tuning thousands of cars on CA 91 octane is that we've seen patterns emerge in the detonation resistance of various brands. The most prevalent observation we've made is that Shell gasoline seems to be more knock prone than other major brands. It isn't that it necessarily makes less power, but it requires an average of 2 deg less igntion advance than, say, Mobil or Chevron.
Since all major gas manufacturers use base stock gasoline from the same common pipeline, it must be something in Shell's additive package, but I can't tell you how many times a customer has come in complaining of a sudden incidence of knock on their cars and we ask a few questions and I'll be damned if they hadn't switched to Shell recently.
You're right to look at the knock sensor as well. GM ECUs have a pretty good knock retard scheme built in. You can still get knock even if the knock sensor is in top condition, but it requires a bad tune (way too much base advance), or a really lean mixture. The only problem is, normally a failing knock sensor will trigger a check engine light and code.
In the end, a carbon build up is the most reasonable argument IMO, but it'll be hard to prove. I'd definitely get the car on the dyno and put a sniffer in the tailpipe. The stock AFR's should be in the low 12's even trending a little richer up top. If they don't perhaps you've got a clogged fuel filter or something.
joefrompa says:
04:07 AM, 01/20/10
Church said some of what I was going to say.
Honestly though, I think your best bet at this juncture (which is to say: the car guy's guide to fixing problems using the cheapest to most expensive manner, in that order), would be too:
1. Add a bottle of redline concentrated fuel system cleaner to a full tank of 91 and 100 octane (sufficient to avoid knock).
2. Then do an italian tune-up: drive the piss out of it and leave it in the upper end of the rpm range for at least 15 minutes straight.
3. Follow that up with an oil change and spark plug swap.
I wonder if this was a modified Z06 that was returned to stock???? Seems very odd to be getting such knock on even a barely driven but well maintained car. I don't have much experience with Z06s, but I know regular corvettes tend to be fairly knock-avoidant....GM does a nice job of tuning the engines to run well on a variety of gases.
Of course, I'm repeating there what Church said. Which makes me think it's an issue of a sensor not working correctly leading the computer to run too much timing.
nomercy346 says:
04:28 AM, 01/20/10
Does it have a tune? If the previous owner had it tuned to only run on 93 this could be the reason. Often the ECU tunes are done in a way that they are not easily overwritten by a dealer reflash to prevent accidental deleting.
lmbvette says:
05:12 AM, 01/20/10
LSX engines need to run on 93 octane...period.
The knocking is a simple fix on LSX based engines. I'm sure there are dozens of tuners out in Cali that can back off the timing on the ECU around 4k and you will have no further issues.
Heck, I have an HPTuners license that happens to work for a 2002 Corvette (includingZ06). I could adjust your timing for you, except I live in Florida.
I'll bet a friendly tuner out there will update your timing curve for free with a simple mention of their name on this blog.
stingray454 says:
06:48 AM, 01/20/10
That's definitely strange, as these engines aren't prone to pinging, and I've never heard it in mine. Mine's been modified and dyno tuned, but I drove 20,000 miles on it stock and never heard pinging then either.
Take it to L.A.P.D (L.A. Performance Division). www.thelapd.com They specialize in tuning Corvettes. They dyno tuned mine after I had the cold air intake and headers installed and they did a great job. I guarantee they'll find your pinging problem faster than a dealer can.
redwoodaggie says:
07:07 AM, 01/20/10
It cracks me up that some people immediately say sell the car, because it has 1 problem. That's the "fun" of buying a used car, you don't know what's wrong and how it's been treated. These people probably buy new Toyotas and sell them the first time anything breaks on them.
roadburner says:
07:22 AM, 01/20/10
I'd add a dose of Techron or BG44K in the next tank of gas. GM Top Engine Cleaner is also good, if it's even still around(I haven't owned a GM product since 1989).
joefrompa says:
07:28 AM, 01/20/10
Redwoodaggie - Significant and recurrent detonation is not "1 problem". On a high performance engine, it can be a simple fix. But if it's been occuring for long enough, the right detonation event can shatter a piston and scrap the engine.
Some people don't like even the possibility of that occurence. Others are willing to work it out. Both are respectable.
ptcdawg says:
07:40 AM, 01/20/10
Agreed, redwoodaggie, sorting them out is half the fun....
deagle13 says:
09:35 AM, 01/20/10
Like stingray454, I had my '07 Vette tuned at LAPD and have had no issues for 2+ years. However, the tuner who handled my Car, Doug, has since left LAPD and opened a new shop: Dynamic Tuning Solutions in Reseda. Also, Charlie at RPM Motors in Santa Clarita has an excellent reputation on the Corvette Forum. I don't think you could go wrong with either one...
stephen987 says:
11:25 AM, 01/20/10
I'm betting on carbon buildup. Too few miles.
stingray454 says:
01:06 PM, 01/20/10
I don't think it's carbon buildup. A - these engines burn very clean: it was classified by California as a "Low Emissions Vehicle" in 2002, and the engine management system was so precise that the LS1 and LS6 did not need an EGR. B - the knock sensor should pick up the knocking even if there was carbon buildup, and adjust the timing and mixture to eliminate it.
I'm going to guess a bad knock sensor, O2 sensor, or possibly defective cat converters (back pressure).
banhugh says:
09:33 PM, 01/20/10
-"I'm going to guess a bad knock sensor, O2 sensor, or possibly defective cat converters (back pressure). "
-"Ka-Ching!"
stephen987 says:
07:12 AM, 01/21/10
The knock sensor and O2 sensor are not particularly expensive parts to replace. But wouldn't either one lead to a CEL?
zoomzoomn says:
02:30 PM, 01/21/10
sodaguy says:
01:19 PM, 01/19/10
Sometimes, pinging can be the result of heavy carbon build-up on the tops of the pistons.
Amen. BG 44K in a full tank of gas. ;)