Glenmhor 1

Hello Everyone,

First post on Rennlist although I have been browsing for a while.

I wonder if someone on the forum that understands how to decipher the rev range excursions would be kind enough to translate this one please?

Operating hours courier. 356.000h

Number of ignitions at speed > range 1. 4369

Number of ignitions at speed > range 2. 370

Number of ignitions at speed > range 3. 1

Number of ignitions at speed > range 4/5/6. 0

The car is a Mezger engine 997.1 with 11900 miles on the clock.

Thank you so much in anticipation.

Zeus993

I'm not an expert in DME's I'm not to offer an opion other than you may want to post this on the 997 site where there is a lot more action and this subject is commonly discussed.
I too will post mine this next week.

wilson234

I just went through this process, while I couldn't tell you specifically how to calculate the number of engine revolutions based on the # of ignitions, you have a solid car, given the fact that you only have Range 1 & 2, with 1 ignition in range 3. From my research ranges 1-3 are prefectly fine, 4 acceptable and 5 or 6 you should be concerned.

Does anyone know how you can have just 1 ignition in a range zone? It appears this car has 1 ignition in range 3, the car I recently purchased had 1 ignition in range 4. Based on my understanding, that would be similar to just one cylindar firing, but at that high of an rpm, it would be very odd just to have 1 firing?????

strato58

How do you get these reports? Im looking at a higher milage car with a vague maintenance history. Can i bring it to any Porsche dealer and ask them to run a report???\ thanks

Zeus993

Yes - a DME report should be part of a good PPI performed at a Porsche Dealership. It's particularly important for a manual transmission as the limiter will protect the engine on the up shift but not on the downshift. PDK cars are by and large immune to over-revs but this apparently may not be 100% true, as per other posts on the subject. The DME is report is an extra +/- $100 and well worth it for some peace of mind on whether the car was trashed by the previous owner(s). High revs can void warrenty protection on engine failure, not that this an issue with the Mezger GT1.

malmasri

you want to stay away from any over revs level 4 or beyond as they indicate damage to the engine is a high probablility at 4 ...definate at 5 ....so if you are a buyer I would make sure that there is a service history for the car and write a check....
If you need technical data go to the 997 GT forum and do a search for DME read outs

TT-911

You do not need a Porsche dealer per se. Any good independent can read out the DME or you could buy a Durametric tool and do it yourself.

To the OP , that is a great DME read out. Perfect car !

Glenmhor 1

Thank you so much for the replies guy's, really appreciate it.

Rob.

C2 Turbo

A friend just traded in a low mileage TT with few over revs in range 4 and 5. The dealer never checked the car for the over revs ( I wonder why not) and it was offered for sale once the Porsche completed the certification on the car ( I wonder why) ?

I have no clue why forum members are so adamant about type 4/5 over revs where as dealers are not ?

May be you all know something that they don't know

atcbi5

100% on that one, I got 19 in the 3, 7 in the 4, wait 2 in the 5 and 1 in the 6. Car has not blown up yet. I have not missed a gear change? Wait, what about owner numero uno? Maybe? Runs like a top

simsgw

The on-board computer records the plug ignitions in what programmers call 'buckets'. That is ranges of values. Anything comfortably below redline isn't recorded at all. The first bucket means "near but slightly above redline" in some cars. In others, the designers chose it to mean "almost to redline". We have people on the 997 forum who assert authoritatively that the range definitions are such and such. Then someone else chimes in with "No they are not. They are..." something else. Confusingly, both will provide references to manual pages and sometimes provide scans of those pages. Arguments ensue as to whose internal Porsche document should be considered more trustworthy.

Another debate, also supported with contradictory documents, is whether the counts are cumulative over time or represent the longest interval the engine stayed in that range. (That is, you might have one brief event that follows a long event. By this hypothesis, the computer will not record the brief event because the long one is more significant.)

I have concluded that the factory changed the definition themselves as their concerns for over-rev varied between engine models. The "engine control unit" or ECU in fact changes with different models so it's quite likely that with experience using this capability the field engineers and the factory design engineers changed their opinion about what information was worth recording.

The one in range three is an oddity we see all the time. It seems to be an 'artifact' as we call such things. I can think of both mechanical and computer/electronic reasons why these appear, but I can't be sure of the exact reason without access to technical data Porsche probably isn't going to give me. Whatever the reason, the ones mean nothing.

What all that means is that we don't know exactly how fast your engine was turning when it recorded those ignitions in range one and two. Using one set of likely numbers I found for the naturally aspirated 997 engine, range one is 7300 to 7500 rpm. At that speed, 4369 ignitions mean the engine spent about twelve seconds there. That would be an awfully long time for a single event, which supports the idea that the count is cumulative. By that same source, range two is 7501-7700 rpm. Still not scary fast, and the engine would have spent only one second in that range. With conflicting documents, and with no data on your own engine, we know those numbers are not precise, but they won't be far off. They are representative of what we're seeing.

The engine is designed to operate at redline and a couple of hundred rpm faster won't damage anything. Certainly not in twelve seconds and -- except for heat build-up that the cooling system might not be able to handle -- not even in several minutes. That's how we choose the redline: the highest design operating speed.

What we do know is that those two DME ranges always act as "oops" recordings in all models. Basically, the driver has gone up to or slightly past the redline, but the engine is not harmed. They amount to "no harm - no foul" ranges. Speaking as an engineer, I'd say they exist simply because we are obsessive about data. Occupational trait of engineers. All it really would tell me is that someone did use the engine like an enthusiast, but absent counts in higher buckets, he was doing it properly. Speaking as a driver, it happens to all of us. My own car has similar readings. You get involved in something that demands your attention and you make a downshift half a second earlier than you should. The engine is accelerated into those ranges past redline by the car's kinetic energy.

An early downshift happens to the best of us occasionally. I've only done it perhaps three times in 47 years of racing, but some people distract more easily. Early downshifts within reason are not a big deal. You can damage an engine severely by an inadvertent downshift, by shifting down to second when you meant to go up from third to fourth. The high end of third is 100 mph and up, depending on the model. Putting the car into second at that speed pushes the engine into rpm ranges from 9000 up. The dynamic loads at those speeds break parts. Which parts depends on a lot of factors, but something will break at 9000 rpm when an engine is redlined in the mid sevens. Probably a bearing will be ruined; maybe a valve will be bent and a piston damaged. Something like that.

No one has done that to your car. One track day, I got a late point-by from a novice, took it when I should not have, and then found myself going into a corner ten mph fast, with an inside line compelling an early apex, and a driver who would probably hit me if I let the car get sideways in front of him. I got preoccupied with all those factors and took my three-two downshift where I usually did, but traveling that much faster. For a tense couple of seconds, two or perhaps three, the engine sounds told me it was at redline and then some. (It shows on my DME but the dealer never gave me the exact counts.) It felt like a week, but call it three seconds and think of it as a typical "early downshift" event. Your car has had something similar happen three or four times.

I was on a track braking down from a hundred plus intending to go into second at around seventy. I screwed up and did it at 75-80 mph instead. A novice can do the same thing on the road by shifting into first. I'm not sure how one does that, but we have reliable self-confessions of it happening. So those range reports don't even mean your car has been tracked. Maybe just a couple of clumsy downshifts on public roads.

If your model has the ECU programmed to record "almost to redline but not quite" or if it has a 'soft' rev-limiting control, then ranges one and two can mean acceleration events. Times when the driver left full throttle half a second too long before shifting. That can't happen with a 'hard' limiter because computers are so much faster than physical movement of the crankshaft that any limit rpm we set is impossible to exceed with power, but many models have a mode of operation that uses a 'soft' limit. Yours might have that. Again no indication of damage. Just a different way to create those counts. And quite easy to do with a Turbo I might add. Things happen very fast at full throttle.

Either way, road or track, downshift or acceleration events, counts in range one and two never indicate damage. If the counts were high enough to indicate the engine spent many minutes at those speeds, they would suggest an abusive driver, but a few seconds in twelve thousand miles is just normal sports car driving.

Enjoy your car and don't worry about the DME.

Gary

TT-911

DME reports are overrated but it's fashionable now
I did not bother with a DME report at all. Have no idea if my turbo 'collected' over revs or not. All I know it performs, uses no oil and drives like a new car.

simsgw

Quite possibly, but we don't have to go there for an explanation. A dealer is interested in making money on each unit, not in buying a car for his own satisfaction. The service department may not even see a car until after the deal has closed for its trade on a sale so profitable the sales manager doesn't care about DME data on the incoming unit. Or in his experience, it doesn't matter in terms of profit. If the service manager screams at the condition of the trade-in, it just goes to auction. If it's a cream puff, they keep it for local sale.

That's the biggest reason their reaction is different than ours as owners or potential owners of a car. But also they look at how long ago the event occurred. Ranges four and five indicate damage is likely, but if the engine has run for forty hours since the last such event, then it's likely that accelerated wear on the bearings and similar effects were all that happened. This is true and affects warranty coverage questions, but I seriously doubt a sales manager considers it at all when taking a trade-in. See the previous paragraph for a sales manager's reasoning.

Gary

C2 Turbo

But a dealer won't sell let alone CPO a car that has potential engine damage by getting over revs in range 4/5/6 or would he ?

I will say it again, if the car has covered 100+ engine hours pass the most recent over revs then what are the chances that it has occured any engine damage?

If the car is too good to pass (value/price/options) but the over revs are concerning to you then go ahead and get a compression/leakdown done and if it passes those then have them put in the new plugs and enjoy the car.

simsgw

CPO standards are set by PCNA and you're right about a high-range DME disqualifying a car for CPO. Beyond that, I won't predict what a dealer might do. With range 5 or 6 counts I would expect that the car would go to auction with other dealers made aware of the situation, but I don't really predict that. Dealers are people too.

As for the likely damage, if the car has managed even forty or fifty hours of operation after the latest high-range event it obviously isn't going to suffer a catastrophic failure. The time for that has passed. I suppose a very slightly bent valve might show up on a compression check but not otherwise. Likewise a broken ring, though I wouldn't have put that high on the list of damage I personally would expect from an over-rev. Somewhere above 9000 we start causing metal fatigue in the rods but I would expect that to cause a failure or dramatic symptoms within that first forty hours. However, the high g-loads at the upper ranges also create extremely high pressures on the bearings. They may have surface damage that doesn't cause immediate failure. Compression checks don't tell us about bearing problems. When they don't fail immediately, they still can initiate the high-wear phase of their lifetime as a result of being over-stressed in one of these events. This would show in oil analyses because the alloys used in bearings have a clear signature.

Let it be noted that cars are just my hobby of sixty years or so. My engineering expertise is in satellites and spacecraft. I don't have access to the field reports that Porsche engineers examine to assess these risks of over-rev damage. I really don't know which is the most likely result and I would expect it to vary with specific engine models in any case. I'm just saying what categories of damage seem likely.

My personal feeling is that I wouldn't buy a car with ranges five or six indicating anything higher than the single '1' that I consider an artifact of the system. Wouldn't even consider it. And I would have to be irrationally in love with a car to consider it with range four appearing, no matter how much of a bargain it seemed to be. I'd rather spend the same money on a less desirable car whose reliability isn't an issue.

If I screwed up and did that to my own car, I'd hold my breath for the next forty hours of operation, start taking oil samples regularly to watch for approaching bearing failure, and... well, I'd consider a sale while the car still looked and sounded great. And hope I found a buyer who feels as you do.

That's just me of course.

Gary