Throttle blip = engine knock???
11-18-2008, 12:54 PM
#16
Burning Brakes
Why do I want to spend twice the cost of an M3 to get a car with the engine in the trunk that knocks when I rev-match? 
Please buy the M3 and enjoy your heavy, bloated, ugly, I-drive infused Bimmer and leave us to complain about knocking.
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11-18-2008, 02:01 PM
#17
Intermediate
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I took the car out today and made it a point notice how I was rev-matching.
Found I'm letting the rev's get too low and being too aggressive with the throttle to bring them back up. The only time it did it today was when I let the rev's get to around 1500 before blipping.
I just need to do it quicker and not let the rev's drop too far.
Found I'm letting the rev's get too low and being too aggressive with the throttle to bring them back up. The only time it did it today was when I let the rev's get to around 1500 before blipping.
I just need to do it quicker and not let the rev's drop too far.
11-18-2008, 08:35 PM
#18
I was just surprised to find out about this now, I have never seen this issue discussed here before. I was also surprised to find how many were saying they noticed this. I've never had an MT car with this issue. Not something I'd expect to have to be concerned with.
10-25-2010, 12:34 PM
#20
FWIW I have this too.. and it drives me crazy. Glad it is not just my car.
Upping the octane to about 96 cured MOST of it, but I still hear it on occasion, and it's simply not worth using 96 all the time.
Upping the octane to about 96 cured MOST of it, but I still hear it on occasion, and it's simply not worth using 96 all the time.
10-25-2010, 01:39 PM
#21
When are you guys getting this knocking? is everyone getting it in the low range when blipping? I don't think I've ever heard it but if I'm heel-toe-ing I'm usually running a just a bit higher than 3k (because I'm usually driving a bit more agressively).
10-25-2010, 10:48 PM
#24
Might make sense to test by leaving the car out of gear in the driveway. Take it slowly up to 6k and let it drop to 2k then blip. Does it still happen? Does it happen with a violent blip? does it happen with a swift but smooth blip?
But I can't make my car do that... I don't have an "s" though. I've heard at least a cough on other vehicles when the throttle is whacked open though.
But I can't make my car do that... I don't have an "s" though. I've heard at least a cough on other vehicles when the throttle is whacked open though.
10-25-2010, 11:32 PM
#25
Race Director
Hi.
So I've put a little over 2000 miles on my 997C2S since I started driving it a little over a month ago.
I always match revs when down shifting any standard transmission vehicle and when I blip the throttle on the 997, it sounds like I'm getting some engine knock just for a second....but I'm not sure because i think there are some clicking sounds in there too. Been doing this since day one.
Anyone else hear things comparable to this when blipping the throttle?
Could it be something other than knock/detonation?
I've used 93 octane since taking delivery.
Car performs great and no engine knock detectable anywhere else....ever.
Thanks!
So I've put a little over 2000 miles on my 997C2S since I started driving it a little over a month ago.
I always match revs when down shifting any standard transmission vehicle and when I blip the throttle on the 997, it sounds like I'm getting some engine knock just for a second....but I'm not sure because i think there are some clicking sounds in there too. Been doing this since day one.
Anyone else hear things comparable to this when blipping the throttle?
Could it be something other than knock/detonation?
I've used 93 octane since taking delivery.
Car performs great and no engine knock detectable anywhere else....ever.
Thanks!
What you might be hearing is some sort of very brief transitory misfire due to the probably lean condition this throttle blipping causes. This might be helped along if the engine controller varies intake valve timing and lift based on the engine's lack of load and sufficiently low enough rpms.
More and more engines -- especially ones intended to be sold in the EU region -- are tuned to deliver as good as possible EU mileage and CO2 numbers. Thus
I believe upon rather sudden throttle opening rather than dump a bunch of fuel in the engine most of which just exits the exhaust pipe (after being burned in the converters which of course heat them up) Porsche has erred on the side of caution and thus a bit leaner mixture is fed to the engine and the engine enters a lean misfire phase.
It is so brief that no misfire codes are recorded or possibly the engine controller has been designed to misfires under specific conditions like this, similar to any misfires that occur when the fuel tank levek is extremly low.
Knock or detonation detection is not complicated and must be very robust. Knock sensors just detect vibration frequencies the engine designers have determined represents imminent knock or detonation. Thus I don't buy the knock sensor/engine controller interaction in this regard is getting confused.
Real knock, detonation if left unaddressed can have a modern engine in pieces in just no time. These are high compression engines and these engines run right at close to incipient detonation cause advanced ignition timing is critical to maximizing engine output, fuel economy, crusing emissions, and enhanced driveability, at lower rpms and loads (30% or so) where most street car engines spend the bulk of there time.
Sincerely,
Macster.
10-26-2010, 01:18 AM
#26
Three Wheelin'
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Frankly I doubt it is knock you are hearing. Knock needs cylinder filling and blipping the throttle is going to result in less cylinder filling not more. Throttle valve opens air speed through the intake slows down and thus less cylinder filling.
What you might be hearing is some sort of very brief transitory misfire due to the probably lean condition this throttle blipping causes. This might be helped along if the engine controller varies intake valve timing and lift based on the engine's lack of load and sufficiently low enough rpms.
More and more engines -- especially ones intended to be sold in the EU region -- are tuned to deliver as good as possible EU mileage and CO2 numbers. Thus
I believe upon rather sudden throttle opening rather than dump a bunch of fuel in the engine most of which just exits the exhaust pipe (after being burned in the converters which of course heat them up) Porsche has erred on the side of caution and thus a bit leaner mixture is fed to the engine and the engine enters a lean misfire phase.
It is so brief that no misfire codes are recorded or possibly the engine controller has been designed to misfires under specific conditions like this, similar to any misfires that occur when the fuel tank levek is extremly low.
Knock or detonation detection is not complicated and must be very robust. Knock sensors just detect vibration frequencies the engine designers have determined represents imminent knock or detonation. Thus I don't buy the knock sensor/engine controller interaction in this regard is getting confused.
Real knock, detonation if left unaddressed can have a modern engine in pieces in just no time. These are high compression engines and these engines run right at close to incipient detonation cause advanced ignition timing is critical to maximizing engine output, fuel economy, crusing emissions, and enhanced driveability, at lower rpms and loads (30% or so) where most street car engines spend the bulk of there time.
Sincerely,
Macster.
What you might be hearing is some sort of very brief transitory misfire due to the probably lean condition this throttle blipping causes. This might be helped along if the engine controller varies intake valve timing and lift based on the engine's lack of load and sufficiently low enough rpms.
More and more engines -- especially ones intended to be sold in the EU region -- are tuned to deliver as good as possible EU mileage and CO2 numbers. Thus
I believe upon rather sudden throttle opening rather than dump a bunch of fuel in the engine most of which just exits the exhaust pipe (after being burned in the converters which of course heat them up) Porsche has erred on the side of caution and thus a bit leaner mixture is fed to the engine and the engine enters a lean misfire phase.
It is so brief that no misfire codes are recorded or possibly the engine controller has been designed to misfires under specific conditions like this, similar to any misfires that occur when the fuel tank levek is extremly low.
Knock or detonation detection is not complicated and must be very robust. Knock sensors just detect vibration frequencies the engine designers have determined represents imminent knock or detonation. Thus I don't buy the knock sensor/engine controller interaction in this regard is getting confused.
Real knock, detonation if left unaddressed can have a modern engine in pieces in just no time. These are high compression engines and these engines run right at close to incipient detonation cause advanced ignition timing is critical to maximizing engine output, fuel economy, crusing emissions, and enhanced driveability, at lower rpms and loads (30% or so) where most street car engines spend the bulk of there time.
Sincerely,
Macster.
And for the folks who hear that little 'tink' sound on light acceleration, please do not worry much about it. Frankly, for the pass three years I have owned my 997.1S, the car had been solidly trouble-free. I am very impressed.
The other day I was talking to my Porsche mechanic, who has been working on Porsche cars for over thirty years. He commented that the 997.1 is one of the most trouble-free reliable 911's of all time.
Regards,
10-26-2010, 10:03 AM
#27
Pro
Similar situation with my 997.2 PDK C4S which I've described earlier on... when blipping or when pushing at lower revs, in normal or sport mode...gon't like at all. Will be heading in for service soon anyway.
10-11-2017, 12:59 PM
#28
Three Wheelin'
Hello all - I have this same issue with a California car and wanted to revive the thread to see if anyone has new data on this topic since 2010.
This is one of the three minor but mysterious annoyances I cant track down since purchasing my 2006 997.1 9 months ago. If I let the RPMs drop below 2500 and blip the throttle I get a pronounced engine knock. It first thought it was an exhaust rattle as it sounds like metal clanking.
Its only happened while acting like a jerk and downshifting from 3rd to 2nd rolling to a stop light. I chalked it up to karma and decided it was best to stop doing that, so problem solved.
However, I'm still curious what the root of this knock is. A lot of people seemed to have a similar issue when the cars were new.
One hypothesis at the time was low octane gas in California (seems highly plausible in my case) but @Macster also hypothesized it was a misfire.
This topic came back on my radar after I found a small speck of camchain guide wear pad (brown/black plastic) in my filter during the last oil change. I also randomly came across a post that mentioned lugging the engine on the early 996 M96 engines was a leading cause the timing chain and IMS issues.
I put 1+1 together and started thinking maybe this "knock" I heard was actually the timing chain slapping against the wear pad...but I dont know what I dont know.
Appreciate any feedback from people that know more than me on the m96/m97 internals.
This is one of the three minor but mysterious annoyances I cant track down since purchasing my 2006 997.1 9 months ago. If I let the RPMs drop below 2500 and blip the throttle I get a pronounced engine knock. It first thought it was an exhaust rattle as it sounds like metal clanking.
Its only happened while acting like a jerk and downshifting from 3rd to 2nd rolling to a stop light. I chalked it up to karma and decided it was best to stop doing that, so problem solved.
However, I'm still curious what the root of this knock is. A lot of people seemed to have a similar issue when the cars were new.
One hypothesis at the time was low octane gas in California (seems highly plausible in my case) but @Macster also hypothesized it was a misfire.
This topic came back on my radar after I found a small speck of camchain guide wear pad (brown/black plastic) in my filter during the last oil change. I also randomly came across a post that mentioned lugging the engine on the early 996 M96 engines was a leading cause the timing chain and IMS issues.
I put 1+1 together and started thinking maybe this "knock" I heard was actually the timing chain slapping against the wear pad...but I dont know what I dont know.
Appreciate any feedback from people that know more than me on the m96/m97 internals.
09-09-2019, 01:05 PM
#30
RL Community Team
Rennlist Member
Rennlist Member
TheBruce, thanks for linking to this thread in another. I had another thought on this - is it only happening on cars with the OEM airbox? I'm wondering if it is the Helmholz resonator in the airbox snapping shut upon throttle blip due to the immediate increase in air requirement from the quick throttle press.
I have never heard this in either of my 997.1 C2S cars and I'm wondering if that's because I don't run the stock airbox - the supercharged car has a Fabspeed J-Pipe intake and the other has the Evoms, which is what got me thinking about the resonator in the stock airbox.
I have never heard this in either of my 997.1 C2S cars and I'm wondering if that's because I don't run the stock airbox - the supercharged car has a Fabspeed J-Pipe intake and the other has the Evoms, which is what got me thinking about the resonator in the stock airbox.
Last edited by Petza914; 09-09-2019 at 01:28 PM.
