mattyf

Actually not even close. I checked mine for fun all the time after a good run up the hills. My badge of honor: 44677 range 1, 3337 range 2, and 60 range 30. Never a missed shift.

jhbrennan

I believe the max is the digital equivalent of 64K.

motopix

65535 - ask me how I know

scorcherjf

Haha... driven how it was meant to be!

But yea, guess that makes sense for a 16 bit system. 2^16=65536 total memory places, so 65535 would be the maximum value given that it starts at 0.

Tj40

Bruce,


My understanding is that it tracks ignitions because very small amounts of time in these higher RPM bands can be damaging to the engine. To your first point the engine will still have an ignition event even though you are off the gas - you're off the gas when you idle and the engine is still going. (Interestingly Porsche use a variation on this in the new turbo Boxster/911 engines to stop turbo lag - take your foot off the gas and it cuts fuel but keeps the throttle bodies open to keep the turbo spinning.)


Also the DME is measuring time between ignitions, and translating this to an RPM number. The engine also typically measures the ignition events relative to Cylinder 1 Top dead center - the engine management typically counts the teeth on the flywheel to time the ignitions. Hence the RPM you see on Durametric is possibly gained from this data - the ignition timing data is a much more fine grained dataset than RPM. You have to have one revolution to measure RPM but there are three ignitions per revolution so by measuring timing between ignitions you can tell if the engine spent one third of a revolution at a certain speed or RPM.


Hence to Quadcammers point I think that you can happily have a report as the first example - a very sudden spike ('money shift') in RPM does not necessarily have to read larger ignition counts in the lower ranges, at least to my understanding as the engine does not have to turn a whole revolution for the DME to log ignitions in a particular range. It's just going to depend on how sudden the spike in RPM is.


Hope this helps!!

Tcc1999

That's pretty cool. I don't have that functionality on my MT GTS. I hit the limiter once at Laguna going around a Miata just coming on to the straight (2nd gear 90 degree turn right where Magnusson and Bergmeiser collided several years ago in the ALMS series). Anyway, it ruined my lap time but was a good lesson about listening to your engine if circumstances don't allow you to glance at the tach.

Bruce In Philly

Very interesting, thank you.

So..... do you ever see erroneous readouts? Are these oddball numbers actually accurate?

Peace
Bruce in Philly

jhbrennan

Thanks for the info - to make sure my understanding is correct you can't get to range 6 without first passing through ranges 1 - 5, etc. so a mis-shift with range 5 or 6 ignitions will also have increased the counter for ranges 1 through 4.

Tj40

Yes to my understanding this is correct. Now how many that get logged in the lower ranges will depend on how sharp the 'spike' in engine RPM is.

scorcherjf

I've seen DME readouts where a money shift event had less readings in the lower range than the upper range. Are those errors?

Tj40

Bruce - I have no data on erroneous readouts and so would not want to pass an opinion. There are lots of factors and you'd have to get down into the weeds on the electronic architecture of the system, of instance did they implement Error Checking on the memory? If not there is a statistical probability of random 'bit flips' inducing errors in the data.


A random error would be truly random though - you are as likely to get 10,000 ignitions in a range by random error as you are 1.


Are small numbers truly accurate? You'd have to understand the sensors in the system and see if there was electrical 'noise' induced that would cause these and where in the system the noise is generated.


So likely they are accurate? I don't know and there are likely other factors I've not considered.


I would run away from a used car with range 4- 6 events though!


Hope this helps...

Glyndellis

Whilst I understand that there is a possibility that an engine could be rapidly accelerated through an rpm range, surely it would not decelerate at the same rate?
For example, the aforementioned shift from 5th to 2nd could spike the RPMs quickly as the clutch engaged. If you then pushed in the clutch, the engine will take time to slow down (inertia effects) and the I would anticipte that over revs would register through the ranges as the engine slows down.
Applying some simple maths to the data listed in post #1, and assuming that the raise through the over rev ranges was instantaneous (probably not possible), this would indicate that the engine slowed from 9500 rpm (range 6) to 7700 rpm (range 2) in around 30 milliseconds (and 4 1/3 revolutions of the crankshaft). I'm no expert, but this seems implausible and supports the idea of a software glitch.

Tj40

Not necessarily - if you 'money shift' the mass and inertia of the car push the rpm up - if you hit range 6 and stay there for 1/10 second you'll log 2700 ignitions in range 6.
Disengage the clutch and there is no gas being fed to the engine as long as the rpm drops through the lower ranges faster than it was held above 6 you would see fewer events in these ranges than in range 6.
Now caveat emptor and see Glyndellis post above I don't know how quickly the pistons decelerate from ~9000 rpm down with clutch disengaged and I suspect that unless someone wants to log the ignition events at or near redline under these circumstances we probably never will!
It is worth noting though that an 'event' even down in range 2 is an extremely small slice of time. 3 ignitions per revolution at 7700 rpm means that a revolution is taking ~12 milliseconds and ignition events are every 4 milliseconds - this is range 2 - below the redline so it kinda makes the mind boggle a bit if you think we are looking at time slices that are below your perception..vs a persons reaction time on a money shift event to push the clutch back in after realizing a mistake..

Tj40

Very valid points!

Johnny DB

One of my cars had each range increase by exactly 1...total BS and technically impossible.