Knocking on 91

autoboy70 · 05-18-2009, 09:29 PM

I just took my 997S in to check out the knocking that had been happening on occasion. It happens when I transition from enough throttle to maintain a cruise at 35-70mph (below 3000rpm) to moderate throttle. It seems to happen the most when I am cruising on the freeway and transition from a cruise to moderate acceleration. Like you were trying to accelerate a bit to get in front of the car beside you to change lanes.

It happens about 4 times on a 20 mile commute and sounds like faint, rapid pinging noise coming from the engine. You can feel it in the gas pedal. It can vary in length from a spit second to half a second.

I took the technician out for a drive hooked up to his computer and the car was running up to -9 degrees of retardation. I got it to make the noise a few times but everything checked out ok according to the computer.

They told me this was a "normal pinging noise" and sent me home with a washed car. Anyone have any experience with this?

Sadiq · 05-18-2009, 09:48 PM

"normal" and "pinging" in the same sentence? :-/ I bet microfiber was not involved in your car wash too

autoboy70 · 05-18-2009, 09:57 PM

Says it right here on the invoice. "Normal operation. Roadtested with customer to produce noise. This is a normal pinging noise."

Maybe it is normal for a 997.1 on 91 but it can't be good for the motor. It does it often enough that I am concerned. I'm headed to the Streets of Willow on the first of June and I wanted to make sure the car was in good working order. I'm sure I will be able to find some 100 octane to mix the 91 with before I get there but it is impractical to do that on a daily basis. I drive this car as a daily. My Subaru Outback isn't nearly as engaging.

Edgy01 · 05-18-2009, 10:02 PM

You're probably in California where you get to pay more for an inferior grade of "premium." So long as California permits 91 to be considered premium we'll have that problem. The anti-knock sensors in these engines are supposedly reactive to the pinging and retard the ignition in near-realtime to reduce the impact to the engine mechanicals.

autoboy70 · 05-18-2009, 10:08 PM

So knocking is normal like male pattern baldness is normal. They're both big problems but we have to learn to accept the hand we are dealt.

MJones · 05-18-2009, 11:24 PM

Interesting and rare problem, which I've never experienced in my previous Carrera S or my current GT3, even with 90 octane, the best I could get at times on a road trip.

Have you tried switching the brand of gas you are filling up with?

They have 100 available at Willow BTW

JFA65 · 05-18-2009, 11:44 PM

Only 91 octane available in my area and no pinging on my 09 S with 3600 miles and track time.

nyca · 05-18-2009, 11:55 PM

didn't Arnold just sign that new law for "low carbon" gasoline for California? If you think the crap they are mandating now is bad, just wait a couple of years.

Hockeyman11385 · 05-18-2009, 11:58 PM

You can buy octane booster that will help. I've used it on a Scuderia that will only run on 93 and it works just fine. I found that one bottle of octane booster per 1/2 tank will do wonders.

helispud · 05-19-2009, 12:10 AM

Our premium in this area is 91 octane. I've never noticed any pinging but then we are at 4000 + feet elevation. Our regular gas is 85 and my Toyota Tundra pickup pings and sometimes knocks on it under high load-low rpm conditions.

It surprises me that they sell 91 as premium at low-elevation parts of CA. Even in Boise at around 3000
feet most premium is 93.

sharkster · 05-19-2009, 01:47 AM

I'd stick to running gas from 76 or Chevron.. the other stations' 91 isn't as good that's for sure. You're in Los Altos and there's a VP station right near you so you can grab a few gallons of 100 to mix in when you like

Macster · 05-19-2009, 02:54 AM

Quote:

Originally Posted by autoboy70

I just took my 997S in to check out the knocking that had been happening on occasion. It happens when I transition from enough throttle to maintain a cruise at 35-70mph (below 3000rpm) to moderate throttle. It seems to happen the most when I am cruising on the freeway and transition from a cruise to moderate acceleration. Like you were trying to accelerate a bit to get in front of the car beside you to change lanes.

It happens about 4 times on a 20 mile commute and sounds like faint, rapid pinging noise coming from the engine. You can feel it in the gas pedal. It can vary in length from a spit second to half a second.

I took the technician out for a drive hooked up to his computer and the car was running up to -9 degrees of retardation. I got it to make the noise a few times but everything checked out ok according to the computer.

They told me this was a "normal pinging noise" and sent me home with a washed car. Anyone have any experience with this?

and depending upon when you look at timing data it can be retarded or quite advanced.

Part throttle load most likely to result in pinging which is not detonation which is what the knock sensors are tuned to "hear".

Do not know what gas you've been using but I've found name brand -- Chevron, Shell, Union 76 -- gasolines the best. Stay the heck away from Arco and Valero and other off brand stations.

Buy from a busy station.

Engine might be due a dose/treatment of Techron. Maybe two bottles, used according to instructions. Follow with an oil/filter service.

Engine deposits can accumulate and interfere with air/gas flow into combustion chamber and this produces improper combustion. Deposits in combustion chamber can also cause pre-ignition and pinging.

Be aware of racing gas. While it is high octane to be sure due to its cost and low demand it can be quite old. High octane gas goes stale quite fast and if you buy it you'll be getting expensive gas that may be hardly much better than fresh 91 octane.

If you can reproduce symptom if you want to test something dump a bottle of Swepco 503 gas fuel treatment in tank.

http://www.swepcousa.com/lubesite/lubepdf/j03856.pdf

If symptom goes away....

If not give the Techron a try.

Also, I notice my car runs much better after a 50 or so mile drive. Even my daily 30 mile commute -- most freeway but 5 or 6 miles city streets -- not the same as legal but high speed (highway speed) "blast" non-stop.

Sincerely,

Macster.

dasams · 05-19-2009, 05:21 PM

Quote:

Originally Posted by nyca

didn't Arnold just sign that new law for "low carbon" gasoline for California? If you think the crap they are mandating now is bad, just wait a couple of years.

Sorry, but you're misinformed. All gasolines in the future (inc NY) will contain increasing amounts of renewable carbon as opposed to fossil carbon. A fuel's octane rating can't tell the difference. dave

dasams · 05-19-2009, 05:35 PM

Quote:

Originally Posted by Macster

Do not know what gas you've been using but I've found name brand -- Chevron, Shell, Union 76 -- gasolines the best. Stay the heck away from Arco and Valero and other off brand stations.

Buying from the majors can make a difference but may also be a waste of money. Neither Valero nor Arco are 'off' brands.

The one variable that no one's addressed is that the posted octane rating is the ave of the 'motor' and 'research' values. You want a fuel with the highest MON which, for example, could test as 86 MON and 96 RON (= 91 ave). You do not want a fuel that is 82 MON and 100 RON because it won't perform well under load. Search 'octane rating' at wiki for a brief explanation.

Experiment with different gas stations and you might find a winner. dave

Macster · 05-19-2009, 06:31 PM

Quote:

Originally Posted by mvd

Buying from the majors can make a difference but may also be a waste of money. Neither Valero nor Arco are 'off' brands.

The one variable that no one's addressed is that the posted octane rating is the ave of the 'motor' and 'research' values. You want a fuel with the highest MON which, for example, could test as 86 MON and 96 RON (= 91 ave). You do not want a fuel that is 82 MON and 100 RON because it won't perform well under load. Search 'octane rating' at wiki for a brief explanation.

Experiment with different gas stations and you might find a winner. dave

Top Tier gas.

Link not working so I can't look this up but IIRC neither Arco or Valero offer top tier gas. This what I meant by off.

Valero's claim to fame is it has refineries capable of refining worst crude stocks for gas and diesel.

Arco just has inexpensive gas as its claim to fame as long as you pay cash. Pay ATM (credit cards not accepted at pumps IIRC) and it is not even inexpensive. My seat of the pants dyno has it labeled cheap gas though. Car does not like Arco gas.

Tried it a few times when gas prices were at their highest and vowed never again.

Your suggestion about trying diff. gas stations could be a solution.

However, I've consistently found Chevron and Shell stations have best gas in my area (bay area).

Sometimes after I've run a tank that I purchased at say Rotten Robbie or USA Gas station -- cause other station not handy and I was pressed for time and needed to just get some gas in car -- then fill up with a tank of Chevron or Shell engine acts like it is young again.

Improvement noticable.

Sincerely,

MarcW.

05-18-2009, 09:29 PM	#1
autoboy70 User Join Date: Jan 2009 Location: Los Altos CA Posts: 33	Knocking on 91 I just took my 997S in to check out the knocking that had been happening on occasion. It happens when I transition from enough throttle to maintain a cruise at 35-70mph (below 3000rpm) to moderate throttle. It seems to happen the most when I am cruising on the freeway and transition from a cruise to moderate acceleration. Like you were trying to accelerate a bit to get in front of the car beside you to change lanes. It happens about 4 times on a 20 mile commute and sounds like faint, rapid pinging noise coming from the engine. You can feel it in the gas pedal. It can vary in length from a spit second to half a second. I took the technician out for a drive hooked up to his computer and the car was running up to -9 degrees of retardation. I got it to make the noise a few times but everything checked out ok according to the computer. They told me this was a "normal pinging noise" and sent me home with a washed car. Anyone have any experience with this?

05-18-2009, 10:02 PM	#4
Edgy01 Poseur Rennlist Member Join Date: Nov 2005 Location: Santa Barbara, CA Posts: 9,945	You're probably in California where you get to pay more for an inferior grade of "premium." So long as California permits 91 to be considered premium we'll have that problem. The anti-knock sensors in these engines are supposedly reactive to the pinging and retard the ignition in near-realtime to reduce the impact to the engine mechanicals. __________________ Dan 06 997S PCCB Hard-Top Cabrio Turq. Blue, Nat. Brn Leather http://www.rennteam.com/photopost/sh...00&ppuser=8756

05-18-2009, 11:24 PM	#6
MJones Addict Rennlist Member Join Date: Apr 2002 Location: Los Angeles, CA Posts: 4,483	Interesting and rare problem, which I've never experienced in my previous Carrera S or my current GT3, even with 90 octane, the best I could get at times on a road trip. Have you tried switching the brand of gas you are filling up with? They have 100 available at Willow BTW __________________ '10

05-19-2009, 12:10 AM	#10
helispud Addict Rennlist Member Join Date: Sep 2006 Location: Idaho Posts: 222	Our premium in this area is 91 octane. I've never noticed any pinging but then we are at 4000 + feet elevation. Our regular gas is 85 and my Toyota Tundra pickup pings and sometimes knocks on it under high load-low rpm conditions. It surprises me that they sell 91 as premium at low-elevation parts of CA. Even in Boise at around 3000 feet most premium is 93. __________________ 2007 Artic Silver Carrera Stone Grey Full Leather Heated Power Seats Bi-Xenon Headlights Self Dimming Mirrors Sport Chrono Bose Sound Last edited by helispud; 05-25-2009 at 03:48 PM.

05-19-2009, 01:47 AM	#11
sharkster Addict Rennlist Member Rennlist Site Sponsor Join Date: Oct 2002 Location: san jose, california Posts: 4,610	I'd stick to running gas from 76 or Chevron.. the other stations' 91 isn't as good that's for sure. You're in Los Altos and there's a VP station right near you so you can grab a few gallons of 100 to mix in when you like __________________ Alex "Sharky" Ross www.sharkwerks.com The Porsche Performance Center for EVOMS, TechArt, HRE, Tubi Phone: 510-651-0300 Email: sharky@sharkwerks.com 2010 997 GT3 SharkWerks Project 2009 997S Sharkwerks ZTADPOL 2007 997GT3 RS SharkWerks ZKERMIT 2006 Cayman S SharkWerks RS350

05-18-2009, 09:48 PM	#2
Sadiq User Join Date: Apr 2008 Location: Brentwood, CA Posts: 577	"normal" and "pinging" in the same sentence? :-/ I bet microfiber was not involved in your car wash too

05-18-2009, 09:57 PM	#3
autoboy70 User Join Date: Jan 2009 Location: Los Altos CA Posts: 33	Says it right here on the invoice. "Normal operation. Roadtested with customer to produce noise. This is a normal pinging noise." Maybe it is normal for a 997.1 on 91 but it can't be good for the motor. It does it often enough that I am concerned. I'm headed to the Streets of Willow on the first of June and I wanted to make sure the car was in good working order. I'm sure I will be able to find some 100 octane to mix the 91 with before I get there but it is impractical to do that on a daily basis. I drive this car as a daily. My Subaru Outback isn't nearly as engaging.

05-18-2009, 10:08 PM	#5
autoboy70 User Join Date: Jan 2009 Location: Los Altos CA Posts: 33	So knocking is normal like male pattern baldness is normal. They're both big problems but we have to learn to accept the hand we are dealt.

05-18-2009, 11:44 PM	#7
JFA65 User Join Date: Feb 2009 Location: Tulsa.Ok Posts: 18	Only 91 octane available in my area and no pinging on my 09 S with 3600 miles and track time.

05-18-2009, 11:55 PM	#8
nyca User Join Date: Aug 2004 Location: new york Posts: 579	didn't Arnold just sign that new law for "low carbon" gasoline for California? If you think the crap they are mandating now is bad, just wait a couple of years.

05-18-2009, 11:58 PM	#9
Hockeyman11385 User Join Date: Jul 2008 Posts: 112	You can buy octane booster that will help. I've used it on a Scuderia that will only run on 93 and it works just fine. I found that one bottle of octane booster per 1/2 tank will do wonders.