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Here is the over-rerv report I recieved from the dealer.
It shows 2 - 4’s, 2 - 5’s and 1 - 6.
Is the 6 even possible in a 2007 C4S (will the rev limiter allow it to rev this high - same question for 5)?
Looks like one quick "money shift" happened at 2962 hours. Had it in the wrong gear when the clutch was let out. That will shoot it right last the rev limiter. Looks like the driver realized it immediately and pushed the clutch in.
I agree with JW911. Happened about 64 hours ago (about +2,200 miles ago), which is a very good amount of time for a potential problem to have manifested already. If the car checks out otherwise, proceed.
Wow... all those high over-revs happened at the same time. Personally, I would request a borescope of the cylinders if I was buying this car. Just my 2 cents.
We’ve talked about this before, the Range 4, 5, and 6 over-revs may be artifacts. I recall posters going into somewhat exhaustive detail a out how it was almost impossible to have just one or two of these level over-revs, and if you money shifted you’d never be able to get the clutch back in quickly enough to get just one over-rev - their thoughts, not mine. I’d say do a search but there is so much clutter on this topic that you’d probably end up with more questions than answers. Also, the rev limiter does not protect you against Range 1 and 2 (and possibly Range 3) over-revs. If you are driving very hard and bump into the limiter there is a brief lag between when the ECU records this and cuts power - the lag results in the over-rev. This is why Porsche is relatively unconcerned by at least Range 1 and 2 over-revs (unless you have thousands and thousands I suppose). Think about it, if Range 1, 2, and 3s were significant, and a rev limiter was intended to keep you below these, then the ECU would force a cutout slightly below red line to compensate for the lag.
But if the over-revs bother you, don’t try and rationalize them away, regardless of what I or anyone else has to say. Best of luck.
We’ve talked about this before, the Range 4, 5, and 6 over-revs may be artifacts. I recall posters going into somewhat exhaustive detail a out how it was almost impossible to have just one or two of these level over-revs, and if you money shifted you’d never be able to get the clutch back in quickly enough to get just one over-rev - their thoughts, not mine. I’d say do a search but there is so much clutter on this topic that you’d probably end up with more questions than answers. Also, the rev limiter does not protect you against Range 1 and 2 (and possibly Range 3) over-revs. If you are driving very hard and bump into the limiter there is a brief lag between when the ECU records this and cuts power - the lag results in the over-rev. This is why Porsche is relatively unconcerned by at least Range 1 and 2 over-revs (unless you have thousands and thousands I suppose). Think about it, if Range 1, 2, and 3s were significant, and a rev limiter was intended to keep you below these, then the ECU would force a cutout slightly below red line to compensate for the lag.
But if the over-revs bother you, don’t try and rationalize them away, regardless of what I or anyone else has to say. Best of luck.
+1 Nearly impossible to imagine how only 1 or 2 ignitions could occur three rev-ranges higher than the rest. Rotational inertia and all that. I would guess those are data artifacts, not real.
There is quite a bit of hysteria when it comes to these over rev reports, even if it is somewhat justified. I have a car in getting a PPI as we speak. This is the over rev report I just received.
Range 1: 1395
Range 2: 97
Range 3: 2
Range 4: 1
Range 5: 1
Range 6: 0
I'm not worried about it at all. Looks like it bumped into redline a few times, and ranges 3-5 seem to be an anomaly.
All the RPM ranges listed on the report are real, the ECM is tracking those really easily, The Carrera S has a Max RPM set at 7300 rpm with full torque cut by 7500 rpm. The saying that it could overshoot due to inertia and so on is not true as the ECM monitors how fast the RPM is raising which could be influenced by how hard the driver accelerate, the gear engaged, the mass of the vehicle and the slop of the road and will prevently reduce the torque to avoid any overshoot.
As I said, the even the range 5 and 6 are real, Range 5 is greater than 8400 rpm and Range 6 is greater than 9500 rpm, so all of them that cannot happen by the engine but when the rotation is induced by anythuing after the engine, wrong downshift gear engaged being the most likely culprit. And saying that 1 or 2 Ignition event are not possible is misleading as it could be an overrev happening from a previous range and the driver reacting to it, it does overshoot to the next range.
All the RPM ranges listed on the report are real, the ECM is tracking those really easily, The Carrera S has a Max RPM set at 7300 rpm with full torque cut by 7500 rpm. The saying that it could overshoot due to inertia and so on is not true as the ECM monitors how fast the RPM is raising which could be influenced by how hard the driver accelerate, the gear engaged, the mass of the vehicle and the slop of the road and will prevently reduce the torque to avoid any overshoot.
As I said, the even the range 5 and 6 are real, Range 5 is greater than 8400 rpm and Range 6 is greater than 9500 rpm, so all of them that cannot happen by the engine but when the rotation is induced by anythuing after the engine, wrong downshift gear engaged being the most likely culprit. And saying that 1 or 2 Ignition event are not possible is misleading as it could be an overrev happening from a previous range and the driver reacting to it, it does overshoot to the next range.
Wrong. It is not possible for the engine to spin to 9500rpm to register 1 Range 6 and then fall from 9500 to below 8400 (Range 5) and only record 2 ignitions in that period.
This report is fine, car is fine, DME reports are way overhyped, etc.
You cannot go into range 5 without passing through range 4 twice. Therefore the number of revs in range 4 must be higher. It is impossible to have the same number of revs as the next range up.
You cannot go into range 5 without passing through range 4 twice. Therefore the number of revs in range 4 must be higher. It is impossible to have the same number of revs as the next range up.
That report is great. Hardly driven.
Cw.
Contact me on PM if you want to know in more details how it's working.
To get back to the first REnnlister who posted the DME report, take it as you want, but current Porsche warrant procedure considers activity in Range 3 and 4 to be potentially problematic (RPM > 7700 rpm) with further tests required: lead down, compression, oil analysis..etc.
Contact me on PM if you want to know in more details how it's working.
To get back to the first REnnlister who posted the DME report, take it as you want, but current Porsche warrant procedure considers activity in Range 3 and 4 to be potentially problematic (RPM > 7700 rpm) with further tests required: lead down, compression, oil analysis..etc.
Thanks
Frederic
Please post what you know right here. It would be very valuable to learn how the crank can spin up and down through 2000rpms and only register 1 or 2 ignitions.
Sorry for the delay in responding.
The DME report is a diagnostic report for the dealer, not mandatory by regulation, so the update rate is more than likely at 10Hz (one processing every 100 ms) which is really slow in the Engine controller world.
And it's important to understand this fact, Ignition is not time based but event based, so the higher the rpm, the shorter the time between ignition event: 3.33 ms at 6000 rpm, 2.66 ms at 7500 rpm and a staggering 2.1 ms at 9500 rpm.
So, knowing that, if you process these event at 100 ms, you are missing 97.4% of the event at 7500 rpm and 98% at 9500 rpm.
Something else to know:
Let's focus on Range 4, 5 and 6
Normal acceleration of most engine in 1st gear is around 2000 rpm/s, if you are in range 4, 5, 6, it means you missed a gear, the acceleration will likely be around 5000 rpm/s, 500 rpm/100 ms (Update rate of the DME report)
and, the spread of RPM for:
Range 4: 500 rpm
Range 5: 1100 rpm
Range 6: just > 9500 rpm
So, if you have one event of missing the gear, the maximum ignitions collected will be:
Range 4: 2 (one at 7900 rpm and 1 at 8400 rpm)
Range 5: 3 (as at worse, you have 1 at 8401 rpm, one at 8901 and the next one will be at 8901)
Range 6: it will depend of how long you are in this range, but moot point as certainly, you will destroy the engine, if you stay more than a few hundred of second, Piston acceleration relative to what the Camshafts can do and the springs will certainly create a close encounter between valves and top of the piston.
Based on that and looking at the data from the customer above, the RPM went above 7900 rpm only once in the life of this engine
That makes sense.
But why would you assume it is at 10hz? That's stupid slow by 2005 standards and doesn't make sense to use in a 100k car where Porsche could use the data for warranty issues....
03-06-2019, 08:52 AM
Over-Rev question
