Did/does anyone ever hear a slight knock when going up 20-30% incline? in 3 years of owning 01 cls, it just happened that my windows were down and much to my dismay I heard it... ie. no loss in power, the car performs fine... and I do not hear it on regular leveled roads... But I put in one of the better 91 premiums i.e. Chevron/Unocal mostly... Asid from flushing injectors with the next fill... any suggestions? could it be air/other sensors that are 'going'... I almost have 40k miles...
I know this is not a biggy.. but in almost 10 years... my 91 integra did not knock even once... and I 'beat the hell out' of that 1.8liter... using same chevron/unocal gas... only 87 obviously ... Thanking everyine in advance for their opinions...

 

Well, the 91 integra doesn't have nearly as high compression - 9.0:1 or 9.4:1 I believe. These motors are 10.5:1 and 91-octane doesn't quite cut it in shitty CA gasoline!

 

What was your speed and/or rpms? Mine will do that sometimes ... a light knock when heading up the hill to the house. If I keep the rpms around 3,000 (2nd gear), no knock. Around 1,500 or so, there is a light knock for a bit. No worry to me ...

 

Try some other fuel as you could have gotten a bad batch.

 

^^

 

Sometimes in some batches as Scalbert mentioned you will get more heptane than octane resulting in detonation or knocking.

"Knocking happens because as you compress air, the temperature of the air increases. The temperature may increase enough to ignite the fuel before the spark plug fires. Cars with turbochargers often need to run on higher octane fuel to avoid knock." - www.howstuffworks.com

Yes we do not have turbocharged cars but we do have high compression pistons which do require higher octane gas. For example if you put 91 octane in your car you have 91 parts octane and 9 parts heptane. Heptane combusts far more quickly than octane, which takes a long time to burn. The more parts octane the longer it takes for the fuel to burn thus allowing for the spark plugs to ignite the fuel and not the increased air temperature in the cylinders to detonate the fuel.

Josh
Excelerate LLC

 

doesn't quite cut in AZ either throw in 110+ weather and a uni-chip, mine will ping on flat roads if you bog it.

 

Lead_sled_dog hit it on the nose... i.e. I was searching for a house going up a steep hill, at around 1200-1500, had to more people in the car [load played the part as well]. I agree - no biggy... But just to mention when I tried out 87 & 89 octane during 'regular driving', the engine knocked quite noticibly at 87, 89 was ok.
I understand the 'reasoning' behind it... but my wife's x5 which I drove cross country and although 91 is 'required' in there... I always put 87 or even 86 in some states... and that thing, maybe less peppy then from 91/93, but hasn't knocked once... no matter what the gas or hill or rpm... and since it's a lease... I use piss-based gas like Arco's...
Personally, I think it's budgeting vs. quality issue... i.e. removing or putting a lessor quality knock-sensor in there, also not many would complain ..

Thanks for everyone's feedback.