Over-revving: Interesting info

[Adam]

I was lurking on the PCA tech site and I learned that not only does the computer log any time an over-rev occurs, it also has different levels depending on how high the revs are. Here is the Q&A.

Question
oil pump shafted breakage/ motor over rev
This occured- accelerated from a traffic light in 1st gear to 4000 rpm, shifted into 2nd gear to 6700rpm then shifted to 3rd gear at 3200 rpm. Noticed a slight shudder in the motor, 5 seconds later display message said take car for service. No red light display. Delivered car to Porsche dealer. Was informed that car had overeved to 9500 rpm, one valve struck one piston head. Motor taken apart, oil pump shaft had sheared off from oil pump gear drive. Parts all over interior of motor.
Trying to tie all these events together. Car was not accidently downshifted at any time at high rpm. I am in agreement that motor overeved (computor log) but am looking for the reason why. Any information assistance would be appreciated. Thanks

Answer
Your description does not indicate a 9500rpm over rev. All 987 and 997 cars utilize a scale for these over revs and a 9500 is a 5 or 6. The over revs are also time stamped by engine hours. The chart below has the different ranges for over revs. There is also a special one called a 10200 that is not shown yet has its own special flag in the VAL or Vehicle Analysis Report that Porsche will run. This is considered by Porsche to be the RPM in which any of their stock engines would be catastrophically damaged.

Range 1: 7300-7500 RPM
Range 2: 7500-7700 RPM
Range 3: 7700-7900 RPM
Range 4: 7900-8400 RPM
Range 5: 8400-9500 RPM
Range 6: 9500-11000 RPM

What you should check is when this category 5 or 6 occurred. It may have been long before this and not had any direct impact on this failure. The pistons have been having issues with breakage and could cause the exact damage that you described even without any over revs.

This type of failure was also common in the older 911 SC pistons in which were cast and not forged.




Scott Slauson - PCA WebSite - 5/20/2008

[timothy]

Is there any way to access the engine over-rev data oneself? I'm thinking in terms of pulling the stats on a prospective Boxster before committing to a PPI.

Originally Posted by timothy

Is there any way to access the engine over-rev data oneself? I'm thinking in terms of pulling the stats on a prospective Boxster before committing to a PPI.

Depending what model year, and were the PPI is done, yes this info is available.

I request this info from the dealership each time I take my car in for an oil change. In the future, I will request this when I purchase my next Porsche, prior to finalizing the sale.

FYI- the 986 Boxster does not have 6 ranges like the 987. I think they only have 3.

[Jaxonalden]

Great post Adam!! Timothy, I just bought a Durametric diagnostic tool that you load software into a laptop and use the supplied cable that you plug into your car. Durametric allows free software updates off of it's site.

http://www.durametric.com/usedporschebuyersguide.aspx

This is that link to Durametrics "Used Car" page that shows you the info you want. The Enthusiast package cost me $250 and for me was money well spent. I had a airbag light that the dealer wanted $100 to clear and with this tool it took me 5 seconds!

[gmboxster]

I'm very much a novice when it comes to mechanical issues. I have a 1998 Boxster. Can you briefly explain how that device you bought can be used to further understand the health of your engine ?

[Jaxonalden]

GMBoxster,

Health of the engine? Good question. As for the diagnostic tool, if you go to the website and click on some of the links it will show you everything that you can see and things you can do. Our 986's are a little limited compared to other Porsche auto parameters that are available. Still allot of good information though. What I like is the real time reading you get with the engine running (dah) from all the sensors along with the same information in bar graph form on the bottom of the page.
For me personally to know the health of my engine I start with a compression check (wet & dry). This will tell me the condition of the rings and valves in all cylinders. If I'm looking at a used car I check the fluids, its a great way to tell how well the car was taken care of.

Hope that's the info you were looking for.

[Tool Pants]

Some more info is here. http://www.renntech.org/forums/index.php?showtopic=20076

[gmboxster]

Thanks for info. I'll do some reading. I want to learn about these cars.