Riccardog

I am looking at buying a used 997 (as per my other post) which has the following readout from the DME for 'over revs':

Type 1: 3570
Type 2: 588
Type 3: 152
Type 4: 69
Type 5: 0
Type 6: 0

My question is, would the "Type 4's" be something to worry about?

Fin Fever

No

gpjli2

If it happened more than 40 hrs of operating time ago and there is no cel or other issue forget it. (This more or less from a service bulletin someone posted at one point)

No HTwo O

Yes. Worry.

I would not buy that car. Do as you want.

Riccardog

Thats useful advice...

For the record, I am having a compression and leakdown test.

No HTwo O

There's a TON of info on Rennlist about over-revs. Use "search" and read the posts. Doing comp & leakdown is a waste of money on this car, IMO. There are 100's of Porches for sale without range 3-6 over revs. Buy one of those.

How many miles ago was the last oil change? Do an oil filter dissection too.

Luxter

Type 4 = 7,900 - 8,400 RPM's
Potential damage to the engine.
Your call....
It actually looks like just one big misshift.
Type 4 = 23 crankshaft revolutions likely in lower range of 7,900 - 8,400 RPM's
Type 3 = 51 crankshaft revs
Type 2 = 196 revs
Type 1 = 1190 revs
Overall not the end of the world.
I would however look elsewhere.
The CPO may be denied if in ranges 4-6 IIRC.

Riccardog

Exactly because there is a TON of information it is difficult to distill it all, particularly with respect to "Type 4s" which seem to be 'on the fence' a bit more than 1 -3 and 5 -6, therefore my specific question.

Having since spoken with 4 different Porsche specialists from OPC to independents (after my post last night) and reading some of the posts on here and 6speedonline, I have gained enough information to assess my options and decide that I will in fact buy this car.

The OPC itself said that a compression/leakdown would be required to allow the car back onto the official warranty and that normally for the type 4's they get allowed back on. So I don't see which facts you base your 'opinion' on?

I also think its a question of how risk prone one is. For me, ~0.1 seconds at 8400rpm max over 47k miles is not ideal but its not also tragic.

If it comes to it the car is sold by a repuatble independent and is warrantied for 1 year. After that I will stomach the cost of a rebuild when it comes (not "if"!).

Quadcammer

when did the type 4 overrev occur?

No HTwo O

Pay to have new plugs put in , and ask to see the old ones.

Riccardog

Ok, this is something that is baffling me. They plugged in the Autologic System and we went to the relevant menu but it only showed the number of ignitions but not the timestamp next to each one. I've been trying to find out online why this could be but there isn't much information.

Any ideas much appreciated!

Yep, new plugs part of the sales deal, though will request them to keep the old ones for me as I hadn't thought of that.

Btw, I take it you're an aircooled guy? Rewind 10 years ago and I was just buying my 964 C2 and became quite a regular on Rennlist (username: Riccardo), those were the days of Adrian Streather, Viken (pcar.com) and some of the other old timers, bet they're all gone now.

No HTwo O

I'm neither an 'air-cooled guy' or a 'water pumper'. I just enjoy my Porsches. But, I am guilty of being a lesbian in a man's body.

Macster

You want to know at what time (engine run time) the overrevs occurred.

I have a couple of AutoXrays laying around. They are good OBD2/EOBD code readers/data viewers but they are not specially designed to work with Porsches.

I believe that only an OPC with a PIWIS (although I think this has been deactivated and now OPC's must use PIWIS2) can not only read the overrev counts but also the time at which the occurred.

If you find the overrevs occured just minutes ago...

But if they occurred hours of running time ago, any damage that the engine might have sustained would have become evident almost immediately.

A leakdown/compression test is nearly useless. The best test you can give the car the engine is a thorough test ride/drive.

You want to ride in the car for around 15 miles while the seller demos the car to you and then you want to take the car out as a driver covering this same route and driving the car in the same way.

This gives the DME time to identify any problems like misfires (from a bent valve for instance) to any problems with any other area of the engine and its population of sensors/controllers.

Sincerely,

Macster.

cello

Macster, I'm curious. Are over-rev caused damage usually "caught" by DME 'faults' in your experience? Wondering because over-rev damage can be in differing forms; the typical bent/misaligned valve to connecting rod stress, etc. BTW, honest question: I dont know the answer.

I do think tho that time/miles from the event can lend confidence that same did not truly damage the engine (or that any warranty would not be honored solely due to same). Maybe paradoxically, I would want to know the engine was run hard (not abused) after the range 4 event. That is, I think it confirming to some extent if the engine were run in high rpm ranges for a decent amount of time post the event and no faults or troubles showed themselves...

OP - No one can foretell. If the potential issue is factored into the price, and you are comfortable that the same represents a deal and a reasonable risk given your intended usage and situation, then go for it...

Macster

Thankfully I have no direct experience with overrevs and damage arising from them.

In almost all cases if there's any damage arising from the overrevs the driver knows about it right now. The engine or pieces of it start to break up. Most often a valve head contacts a piston and the valve head comes apart from teh valve stem and that's that.

In other cases the valve or valves get bent and the engine will manifest misfires.

In most engines what limits its max obtainable rpms (and after obtaining these to continue to function with no after effects) is when the valves float. (As an aside, my 02 Boxster has a redline of 7200 rpms. Even today with over 250K miles on the engine it occasionally gets taken to redline, and once in a great while I even hit the rev limiter. Valve springs are an amazing bit of hardware!)

Now the DME constantly measures the speed imparted to the flywheel by each cylinder on its power stroke and if the DME detects an under (or over) performing cylinder over a rather brief span of time it will turn on the CEL and log one or more misfire error codes.

This overrev business has been discussed quite a bit and the other day -- well weeks ago now -- I asked a very experienced senior Porsche tech what is considered acceptable and what is not acceptable.

He said (paraphrasing) the overrev counters don't matter as long as the engine is not exhibiting any signs of trouble and the engine has been run some times since the last overrev event timestamped.

At the dealer service department, if a car comes in with a sick engine and there is a warranty claim the overrev counters are read to see if there was an overrev event, one that was caused by a missed shift. The presence of overrevs in the higher ranges can be reason to deny the warranty claim. He did not provide any details.

For us layman, the tech told me that before buying any used Porsche the engine must be run long enough, under varying scenarios to give the DME a chance to detect and flag any issues that may have arisen from an overrev in the higher ranges or any other issues the engine or its population of sensors/controller may have.

Briefly, the car must be driven a total around 30 miles. In this time over this distance the DME will run a series of tests testing the misfire detection system, knock control, O2 sensors, converters, vapor recovery/tank ventilation and one or two others. In some cases the tests are run twice.

As long as the engine behaves, as long as the CEL remains off (and that this bulb does come on when the key is turned on and goes off when the key is turned to engine start and the engine fires) the engine is healthy.

Now the tech said the overrev counters don't matter... But they do matter, at least to me, and I'll explain: What the overrev counters say to me is how the car was driven, treated. A few (some) overrevs in the lower range doesn't bother me. If I come across a car with lots in the lower ranges and even some in the higher ranges, even if the engine would pass with flying colors the 30 mile ride/drive test I'd be leery of the car because I would suspect it had been driven hard. But each buyer or prospective buyer has to make his own determination what he will and will not accept of a used car.

Sincerely,

Macster.