When I'm climbing a hill at a slow speed in my 05 A4 I get what sounds like pings under the hood. I have had some engine mods done (H/C/tune). But the engine runs very strong. Anyone know what could be causing the sound? I run on Chevron premium - which in Ca is 91 octane.

 

I'd suspect the tune. The car shouldn't knock on 91.

 

I have a tune aswell, asnd always put in a can of octane booster with 91 gas.

 

The car is sold as being adaptive to octane. It should not knock on 87 but could be expected to have less power. Knock is not a good thing. However, if the car is still under warranty potential damage would be covered and the next owner would have to worry about it out of warranty. I'd never own a C6 out of warranty for long anyway.

I suspect that the 'underhood mat' is partly about muffling knock that the electronic sensors can't totally control.

Put some 87 in the car and see what happens. If it's still under warranty take it to the dealer with a full tank of 87 and tell em to fix it. The general says it don't matter none.....

 

The car is adaptive, but not if someone has been in the computer messing with its programming. The EPA, and GM, call that tampering with emissions control systems. That will void the warranty, and opens the owner up to Federal fines.

 

Adaptive only to an extent. ie it can reduce timing and power. But consider preignition. That is spark knock that was initiated prior to the spark plug firing. Then the two flame fronts collide and knock. You can reduce timing all you want and it will still preignite if the cause of the preignition is still there, such as low octane fuel or combustion hot spots.

91 is marginal for even a stock vette. Aftermarket tuning where they have probably bumped up the timing, it will knock. I think your going to need octane booster or a retune or back to stock tune.

No way in heck should you put 87 in it, unless you like to see holes in the pistons.

 

91 octane really is too low for the LSx series of engines. Hib Halverson even wrote it in one of the first articles on the C6 when it came out:

http://www.corvetteactioncenter.com/...05/intro4.html

Here is the paragraph I'm referring to:

 

I've had instances of pinging in my LS6 and LS2 cars with consistent use of 92 octane fuel, and I have the stock tune in both cars. I've switched gas stations a few times to ensure it wasn't the fuel. The pinging occurs only on hot days with large throttle inputs, and usually with the air conditioning running. I've reluctantly come to see the pinging as normal. I write it off to an ineffective knock sensor system design.

 

I'd take it back to the tuner. There are several threads in the Z06 section related to engines that grenaded after an agressive tune.

Sounds as if the tuner is pulling too much retard from the timing, but that's only a guess on my end.

Good luck.
Don

 

negative on the ping, in my 07 with 91 octane.

 

I had that problem with my C5 and can only suspect ARCO gas. That seemed to be the common denominator.

Use only Chevron in the C6 with no problems.

 

I have a lot of experience with octane, pinging, thanks to a few years running BB's. All fuel of the same octane rating do not react the same. That R+M /2 on the pump can be arrived at in many ways so playing with the fuel brand is imperative. Also it is best to keep the car in a low enough gear so as not to cause lugging. Never use O/D under 60mph with an A4. Not only for not pinging but for transmission life expectancy. Lugging is very hard on the trans.

 

The only fuel I have used is 93 octane and have not had any pinging problems.

 

I run 91 in my 05 have 13000 mi. on it, and not one time have I had pinging, not even on a very hot day.

 

Hib's information may have been preliminary...the published compression ratio in the GM service manual is 10.9:1. In any event, the car is still doing an amazing job of managing the engine at that compression ratio.

He is correct that western states are likely to only have a maximum 91 octane gasoline, but ususally it's because of higher altitudes. I run Chevron premium 91 octane with no audible evidence of pinging even under hard acceleration (stock tune), but my elevation is about 3000-4000 feet above sea level.

As shopdog first said, I suspect the tune is going a bridge too far...I believe I would have the tuner dial it back a notch or two. Seems like I recall one case of grenaded engine here that was tuned; and no, the aftermath is not covered by warranty.

 

In fact the Chevy website says to use 93 octane, not 91, in the C6 (!) for best performance. And that's what I use.

 

My C5 would frequently (I should say usually) ping on 91 octane gasoline. Mixing in some 100 octane to get a tank of appx 93 or 93.5 octane would cure the problem. And, as expected, my local dealer gave me the "it's normal" story. I finally retarded the timing a few degrees, using a Predator, and the problem was solved once and for all -- no more pinging on 91 octane.

My C6 will occasionally ping ever so slightly on 91 octane. Most of those times, it pings only once (i.e., you can hear the marble hit the side of the coffee can only one time). Then the knock sensors pick it up and the timing is immediately retarded enough to stop further pinging. This, I would guess, is exactly how the system is designed to operate. I don't think the average, non-sensitized ear would even notice this small amount of pinging, but it is there.

A local tuner told me that, when knock retard is applied, ignition timing is typically retarded more than required to eliminate the pinging. When he tunes a car (they're usually not stock, though), he adjusts the timing and fuel parameters such that no knock retard is present when the desired fuel is being used. Again, I'm guessing, but I think the average stock engine would require 93 or 94 octane to eliminate occasional knock retard altogether.

 

I ping a bit on 92... totally stock. I do, though, have an ear for ping.

 

Definately talk to your tuner. It shouldn't be doing that unless you got low octane/bad gas.

That doesn't suprise me, especially since Arco is usually the cheapest stuff around. When I got a tune, I was told to stay away from Arco and Costco.

I stick with Shell and Chevron and have never had a problem. Looks like my first post-tune trackday is gonna be in a couple weeks, so for that I'll add some octane boost or a few gallons of 100 octane to be safe.

 

91 is the highest we can get in California.
I always buy Chevron from the same station. No issues.
Bought Shell once, and a little pinging.

Both are top tier gasolines.

Coulda just got a bad batch I suppose.

Try a few different brands and see how it goes.