Here is a 09 Turbo dme report for a car currently undergoing the CPO process. Feedback solicited.

 

I'd pass, with over-revs in range #3 and #4. There are better Porsches out there. There should be a time-stamp on the most recent incidents, too. This report does not look right. Maybe it is the formating.

 

For example, look at this DME report, with the time stamp (in hours) after the range #1 ignitions:

https://rennlist.com/forums/997-gt2-...print-out.html

 

Hi everyone, this is the reading of the 997 C2 i'm looking at :
Range 1: 8274 1455.2
Range 2: 2307 1455.2
Range 3: 667 1379.6
Range 4: 266 1346.4
Range 5: 0
Range 6: 0

Total hours: 2060.5 (mileage: 55k)

What do you guys think ? Thanks.

 

If the dealer CPOs it then they know it is ok and will warranty it.

 

Seriously?

 

Waaaaaaaaaaay too many assumptions. At least 3.

 

The info is missing the time stamps at which the overrevs occurred.

I'm not as dead set against cars with overrev counts as I was.

Provided the overrevs didn't just happen, provided the engine is healthy and verified by an extended idle warmup and test ride/drive covering around 30 miles or so, and provided the rest of the car is suitable condition, the overrevs per se wouldn't put me off the car.

You must be sure you give the engine enough run time when you look at the car to give the DME time to identify any issues with any sensors or with the engine. With overrevs I'm thinking misfires but even with overrevs the engine could be fine but the converters shot due to some unrelated reason.

Be sure to verify the CEL comes on when you turn on the key and make sure it goes out when the engine cranks/fires. Be sure all the other warning lights come on and behave appropriately too.

After the test ride/drive the OBD continuous ready monitor status should be checked to verify the readiness monitors have all been tested and found good. At this time you would want to verify the MIL (malfunction indicator lamp) status is 'off'. Because you checked/verified the bulb worked when you first started the engine this might seem a bit overkill but just in case the bulb burned out during the test drive...At the same time a check for any pending errors is called for too. The guy doing the PPI should do this without asking/prompting. If you're savvy and equipped with an appropriate OBD2 code reader you can read the MIL status, readiness monitor complete status, check for pending errors, etc, before and then after you test drive the car.

The concern I have from a car with a high count of range 1 overrevs and any overrevs in the higher ranges is these indicate the car was well, driven hard. Now this may not be a big deal, but you have to consider how the car was treated, possibly treated, given the overrev ranges and their counts.

Given two otherwise identical cars the one with the fewer overrevs the better. But if the cars are not identical, if the car with the larger number of overrevs checks out to your satisfaction and that of the person performing the PPI there is no reason to shun the car.

But I can't stress this enough, you must subject the car to a thorough test drive. Just a quick run around the block ain't good enough.

Sincerely,

Macster.

 

At any given time, there are 100's if not 1,000's of Porsche for sale. Why buy one with over-revs beyond the normal range (range 1 and range 2) is beyond me? Regardless of a CPO.

 

True...but I think a lot of perfectly good cars are being rejected because of over-rev reports. When I bought my first 911 (71 911T) I didn't know what an over-rev was and even if I did I don't think the technology exisited then to report. But I had a mechanic do a 70's version of the PPI and bought the car. I'll be the first to tell you that I suffer angst with over-revs too. My current car has suspect over-revs but they happened early in the life of the car and the dealer provided a CPO warranty after disclosing the over-revs. I've since put 8,000 miles on it this year and it has been flawless. Over-revs are not a new henomenon so how did all the 911's in the 70's 80's and 90's get sold with no knowledge of over-rev history. I've stopped worrying about it especially since I've found that the Durametric tool I regulary use to check isn't all that accurate anyway.

 

I think one difference is a Porsche from the 70's with maybe, what, 150 HP with a very robust engine is a lot different than a late model Porsche with a "robust" engine and now pushing 400 HP.

What make you think the Durametric tool is not accurate?

Overall, we are on the same page.

 

Sometimes I'll take a reading from the Durametric before and after I leave the car for service (I know, how ****) and I've had instances where the after reading shows 5 additional ignitions in range 1 and then 1 additionnal ignition in each of ranges 2, 3, 4 and 5. This has happened a couple of times and I have no clue how you can get 1 ignition across 4 ranges. Also, I've had 1 ignition show up in those ranges with just me driving and I know absolutley I was never near the rev limiter. Someday I'll let Porsche do a PWIIS reading and see if it ties to the Durametric - numbers are small, the car runs great (no leaks, no oil usage, no strange noises) so I've stopped worrying aqbout it.

Maybe a rhetorical question but how do buyers of other high performance cars like BMW, Corvettes, Nissan, etc. deal with the over-rev questions - this isn't just a Porsche issue is it?

 

I bet they have "black boxes" too for warrenty claims, alone. Other here will know for sure.

 

Damage from overrevs does not respect engine output.

In fact, I dare say an engine making 400hp would be less likely to suffer damage from overrevs compared to an engine making 150hp.

There's no reason to put 'robust' in quotes regarding late model Porsche engines. These engines are putting out in some cases 2 to 3 times the HP theier older counterparts were putting out and these modern engines have to be robust to do this, from the first engine start to thereafter.

Primarily the damage from overrevs is from valve float and all other things being equal an engine with heavier valve hardware will suffer from valve float at a lower rpm and subsequently is at risk to damage from overrevs at a lower rpm threshold than one with lighter valve hardware.

Our modern engines have pretty light hardware although they do have those zero-lash lifters now compared to older engines with their mechanical lifters. However, Porsche has done a good job of making these items strong, yet light.

One thing that owners who like to experiement with different oils, weights of oils, fail to consider is that a heavier oil may make the engine more prone to overrev damage because the heavier oil adds drag to the valve lifter and can keep the valve from closing as fast as it should.

The valve spring has to close the valve but to do this it has to move not only the valve, but the weight of all the valve hardware on top it, between the valve stem tip and the camshaft lobe. This is the lifter but it is also the hydraulic friction of the lifter bucket in the bore in the head.

Sincerely,

Macster.

 

I have no direct experience with other cars in this area but my WAG is they do it about the same way.

All car makers at least those that offer manual transmissions have to be concerned about overrevs due to a missed shift and subsequent engine damage and a warranty claim.

Also, there is some value to this data (along with a multitude of other data the DME collects/stores) to the factory which probably gets the data when the vehicle is brought in for a service or warranty claim and this data is downloaded from the engine controllers (and other controllers) and shipped to the factory which puts the data into a database for on-going analysis.

Sincerely,

Macster.