Knocking on 91
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Intermediate
Joined: Jan 2009
Posts: 36
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From: Los Altos CA
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?
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?
Thread Starter
Intermediate
Joined: Jan 2009
Posts: 36
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From: Los Altos CA
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.
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.
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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.
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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
Have you tried switching the brand of gas you are filling up with?
They have 100 available at Willow BTW
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From: Idaho
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.
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.
Last edited by helispud; May 25, 2009 at 02:48 PM.
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From: san jose, california
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
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Joined: Sep 2006
Posts: 19,035
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From: Bentonville, AR
9 degs. retardation can be normal. Timing quite dynamic....
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?
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?
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.
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From: Coachella Valley
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
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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
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From: Bentonville, AR
By off I was referring to my recollection neither station offered...
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
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
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.
