What is the current state of the 'engine stumble' issue?
12-11-2015, 10:45 PM
#136
Burning Brakes
12-12-2015, 12:40 AM
#137
12-13-2015, 01:22 AM
#138
Rennlist Member
Thread Starter
I was just driving my 16 GTS today and really paying attention to the RPMs. I can't help but think it has something to do with 'hanging out' in the lower RPM range. It 'feels' like the motor is built to live in the 3500 to 5K range. Everyone knows that you're not supposed to lug these engines but I wonder if the stumble, which seems to always occur below 3K RPM, has something to do w the ECU dealing with lower revs. Does this make sense?
J
J
12-13-2015, 06:15 AM
#139
I was just driving my 16 GTS today and really paying attention to the RPMs. I can't help but think it has something to do with 'hanging out' in the lower RPM range. It 'feels' like the motor is built to live in the 3500 to 5K range. Everyone knows that you're not supposed to lug these engines but I wonder if the stumble, which seems to always occur below 3K RPM, has something to do w the ECU dealing with lower revs. Does this make sense?
J
J
12-13-2015, 10:52 AM
#141
It's definitely rpm related and not speed related.
At 75-80mph at around 2500-2600 rpm in 7th gear (on a very slight incline) I can replicate a prolonged and persistent stumble, which manifests itself in the form of a fishing line tug sensation, or a very mild but continuous misfire.
Unfortunately there is no way to record the sensation, nor is there any definitive change in engine noise.
It feels like fuel or air starvation.
When accelerating moderately in 2nd gear, it stumbles without fail between 2500-2600rpm.
At 75-80mph at around 2500-2600 rpm in 7th gear (on a very slight incline) I can replicate a prolonged and persistent stumble, which manifests itself in the form of a fishing line tug sensation, or a very mild but continuous misfire.
Unfortunately there is no way to record the sensation, nor is there any definitive change in engine noise.
It feels like fuel or air starvation.
When accelerating moderately in 2nd gear, it stumbles without fail between 2500-2600rpm.
In Germany one of the most import efficiency statements is going in a straight line 90 km/h precisely. Fuel consumption at this specific speed is still a major sales influence. Although technically the governments moved on to slightly more useful measures it is still in use. And I think it was in much more use during the time that the direct injection engines for the post-M97 era were developed.
For me this specific bit pushes the whole affair more into a software corner where the car is tuned to perform well on specific artificial benchmarks.
Last edited by squid42; 12-14-2015 at 09:03 AM.
12-13-2015, 12:52 PM
#142
For a c2s manual 2500-2600 rpm are translation to cruising with 90 km/h. In 5th gear 2500 rpm is 86.9 km/h and 2600 rpm is 90.4 km/h.
In Germany one of the most import efficiency statements is going in a straight line 90 km/h precisely. Fuel consumption at this specific speed is still a major sales influence. Although technically the governments moved on to slightly more useful measures it is still in use. And I think it was in much more use during the time that the direct injection engines for the post-M97 era were developed.
For me this specific bit pushes the whole affair more into a software corner where the car is turned to perform well on specific artificial benchmarks.
In Germany one of the most import efficiency statements is going in a straight line 90 km/h precisely. Fuel consumption at this specific speed is still a major sales influence. Although technically the governments moved on to slightly more useful measures it is still in use. And I think it was in much more use during the time that the direct injection engines for the post-M97 era were developed.
For me this specific bit pushes the whole affair more into a software corner where the car is turned to perform well on specific artificial benchmarks.
12-13-2015, 04:02 PM
#143
Rennlist Member
I was just driving my 16 GTS today and really paying attention to the RPMs. I can't help but think it has something to do with 'hanging out' in the lower RPM range. It 'feels' like the motor is built to live in the 3500 to 5K range. Everyone knows that you're not supposed to lug these engines but I wonder if the stumble, which seems to always occur below 3K RPM, has something to do w the ECU dealing with lower revs. Does this make sense?
J
J
spend their life (courtesy PDK programming) keeping in that rpm band usually
in 7th gear!
12-13-2015, 04:03 PM
#144
Rennlist Member
12-13-2015, 04:25 PM
#145
Track Day
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Look at my specific thread on the topic.
turned out to be a faulty "magnetic valve lifter" which they fixed on warranty, and now its buttery smooth throughout the rev range in any mode, warm/cold, part/full throttle.
So no more stumble after the replaced valve lifter for me!
12-13-2015, 04:31 PM
#146
I have attached the results of a survey taken about a year ago.
Stumble Survey Results.xls
12-14-2015, 04:58 AM
#147
Burning Brakes
12-14-2015, 01:38 PM
#148
yes my EU 2S 20,000miles had it and it got progressive worse untill I got the engine fault messages and it stumbled like crazy and had an awful rough idle.
Look at my specific thread on the topic.
turned out to be a faulty "magnetic valve lifter" which they fixed on warranty, and now its buttery smooth throughout the rev range in any mode, warm/cold, part/full throttle.
So no more stumble after the replaced valve lifter for me!
Look at my specific thread on the topic.
turned out to be a faulty "magnetic valve lifter" which they fixed on warranty, and now its buttery smooth throughout the rev range in any mode, warm/cold, part/full throttle.
So no more stumble after the replaced valve lifter for me!
Can you please elaborate after how many miles your stumble started?
Is it at the same rpm spot every time.
Most of us do not have a rough idle, so I'm not sure if these are related.
Thanks in advance...
12-14-2015, 01:45 PM
#149
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the rough idle was only associated with the issue with the engine light described in this thread:https://rennlist.com/forums/991/8986...idle-help.html
after the fixed the valve lifter that caused the rough idle/misfire, the stumble was also completely gone.
12-14-2015, 07:38 PM
#150
Thank you for the clarification.
I didn't realize that a valve lifter could be kinda bad with no error codes until an almost complete failure.
I was under the impression that it's pretty binary in its operation.
I didn't realize that a valve lifter could be kinda bad with no error codes until an almost complete failure.
I was under the impression that it's pretty binary in its operation.