NoPasaran

Today I was on unlimited A81 on the way to Stuttgart, Germany.

Generally, I am on German autobahns maybe twice a year and today was one of those times.

My car is manual, 2007 Turbo, with 570hp and 550lbft, stock clutch is 9000 miles fresh (everything was changed, including the flywheel).

First, I accelerated in 6th gear, not putting pedal to the metal, but depressing it at least 50%, I was already going above 125mph, enjoying the noise and acceleration, when suddenly the car "sneezed" (strange noise from the engine), there was a plume of gray smoke from the tailpipes (as far as I could see at that speed) and the car jerked, as if it was suddenly pulled backward. I immediately backed off.

Later, trying to accelerate with more than 50% depressed gas pedal in 5th, I again had this "pulled backward" thing, but no smoke. I backed off. And I had this happen again in 6th gear when I again tried to accelerate very vigorously by keeping gas pedal planted to the floor.

I am not happy. Sure, the car accelerates fine as long as I keep the gas pedal depressed about 1/3rd or less, but REALLY accelerate in 5th and 6th by keeping pedal to the metal I cannot do, for fear of this strange behaviour.

What can it be? Is it the tuner's map? Is it AWD shuffling the power around? Is it clutch slipping (I doubt because I do not see rpms suddenly increasing while the car is not accelerating)?

I guess most of you guys do not go at these speeds, as you live in the States, but maybe some of you have experienced something similar and can share the knowledge?

(P.S. On the positive note - consumption is great, noise is amazing, behaviour at high speed on bumpy roads is sweaty, my windows were getting steamed up, so I had to open them when there was construction on the road and speed dropped to 55mph or so, sweaty but still very sharp. I love Porsche, it is so original!)

atcbi5

Sounds like rev limiter is coming on early due to bad programming.

ca993twin

The rev limiter ummm... limits revs. It is not sensitive to throttle position or load, which is the problem as the original poster states.

Kevin

Sounds like the ECU started to dump fuel.. This usually is done when knock retard is engaged. You also could have felt the ECU enduced throttle intervention. ECU/engine protection. Bad fuel, not enough fuel (fuel pump failing 1 of 2)

Call your tuner and see what he recommends.

ChristopherG

Single cylinder misfire under load from an ignition coil going bad possibly?

Macster

Don't be too sure some of us Turbo owners in the USA don't enjoy autobahn speeds once in awhile...

More than once in my 996 Turbo I've been up to <static> and beyond <damned static again> and I have never had the engine react like you describe yours reacting. The engine in my car pulls like a locomotive until I run out of road or courage. I haven't quite obtained the factory V-MAX yet but I've gotten close enough...

Couple of thoughts, some have been covered already...

The tune could be contributing to this behavior directly or indirectly. But how to eliminate this possibility I can't think off hand other than if possible/viable to revert back to a stock tune -- unless other mods to the engine, turbos, intake or exhaust systems require the aftermarket/custom tune -- and see if the engine still behaves the same.

That is unless you feel the behavior is the early sign of possible engine trouble in which case the last thing you want to do is take the car up and down the autobahn at any speed.

Absent a CEL even if momentary I'd have to (probably) eliminate coils and plugs. But I note with that much tune both coils and plugs need to be in tip top shape. 9K miles given the aggressive tune might just be all the plugs can handle.

And a good point was made about gasoline. Of course you want to run a quality gasoline, the right octane rating and the tune may change the engine's octane requirements so read the tune fine print, and the gasoline wants to be fresh, fresh, fresh.

Another thought is that you admit to only getting on the autobahn twice a year one has to wonder the type of driving the car experiences the rest of the time.

You may have just encountered some engine cobwebs being blown out.

Sincerely,

Macster.

biglicks

I had a simlar problem with my 6tt on Saturday. Another suggestion I have had for the cause was heat build up. Mine ran fine for a while up to 170mph then when I tried again it behaved a bit like a rev limiter coming on (I wasn't near the rev limit) Unfortunately I don't know who did the tune in mine, so cannot go back to them to discuss.

Any thoughts on the heat theory?

Steamboat

I would only hazard a guess that the smoke is indicative of something letting go inside your motor and allowing a larger than normal quantity of oil to enter the exhaust system. The rest of the symptoms would be the ECU pulling timing, lowering boost, etc. in an attempt to prevent further damage. I would flatbed the car to a competent shop for a complete diagnosis.

L_perm

Put very simply, it sounds like combustion occurred when it wasn't supposed to, and the ECU shut things down a bit for safety.

Could be any number of things that caused it, many of which have been mentioned.

IMHO, if you can drive it without having the problem, and nothing else has changed, then you can drive it to your favorite shop. But, I wouldn't drive it anywhere else. I would also call your tuner and discuss.

Good luck,
Louis

Macster

It is a theory.

My thoughts?

Well, if it has any validity it was probably not due to just heat build up.

This assumes the car's cooling system is in tip top shape. Among other things -- like absence of any leaks -- you must be sure both radiator fans are working. These have known to quit and under milder driivng there is no real indication that one has quit.

Anyhow barring a problem with the car's cooling system, absent any signs from the coolant temp gage of a abnormal rise in coolant temperature or even a overheating warning light the engine temp was I believe just fine.

Porsche has done a very good job (better than good jog) on the aerodynamics of these cars -- the 997 a step or two above the 996 Turbo in this regard -- and if any car can take a sustained high speed run it is the 997 Turbo.

So if we consider your theory we can eliminate the engine's cooling system and the DME's reaction to an over temperature condition.

This leaves us with the tune.

Let us assume the aftermarket tune is not flawed or buggy.

Thus the engine's behavior could have arisen from the tuner just being cautious and in fact following the factory's lead in this area.

The factory/stock "tune" limits how long an overboost condition can last -- 10 seconds IIRC -- and then dials this overboost away and will not let it happen again until the throttle has been closed as would the case upon an upshift.

This is to protect the most exposed of the engine components -- valves, pistons, turbos -- from the prolonged effects of the higher heat load from the overboost. This dialing back also expresses a concern for the mechanical limits of the various pieces of engine hardware too.

The aftermarket tuner could have followed Porsche's lead in this regard and after some time with the engine running above a high load threshold the tune could have then limited throttle opening or adjusted timing or even gone into some kind of limp mode injecting fuel only every other intake cycle to allow the overheated engine components cool down.

In the milder from of overboost a close of the throttle is enough. When the overboost (if you will let me call it this arising from the aftermarket tune) is used a brief close of the throttle may not be sufficient to allow the overheated engine components time to recover so a more lengthy and more drastic/obvious dialing back of the engine's output is required and you encountered this.

So, you have a theory and frankly it ain't a bad one.

Sincerely,

Macster.

L_perm

You do have EGT sensors that will alert the ECU to shut things down if temps get too high. Depending on what mods you have, an aggressive tune might cause too much heat in one run to 170. Ambient conditions matter too. How hot was it? Do you have a high flow exhaust, upgraded ICs? A plugged air filter can cause problems too. Were your oil and coolant temps normal?

Just some things to think about.

Louis

Zeus993

Any update for us?

biglicks

not from me. I am in the middle of replacing my unknown tune with one from UMW. Currently running standard performance map.

For info, I have a completely standard engine, exhaust, IC's. Outdoor temps about 15deg C. Kevin at UMW did say "your previous tuned file did have some knock retard on the few minor 100% throttle "tip ins"" so does indicate something going on. In car I had no CEL, codes etc, normal gauge temps and was running 100ron fuel.

Sorry NoPasaran, I appear to have highjacked your thread a little, got involved when it was suggested we may have a common fuel issue, given our locations, therefore corss posting may be useful to us both.

Steve

NoPasaran

Thank you all for your comments.

Forgot to mention, I had no CELs during the drive.
Gasoline was Shell V-Power 100, full tank. I doubt it is fuel pumps, while I often run the car with very little gas as well (good for another 60-70 miles), so both pumps are working.
The car was tuned when it was 2000km old and plugs were changed according to Porsche manual at 60000km, and the car was running just fine inbetween 2000 and 60000, so plugs must still be OK.

The tuner, Sportec, has 15 years experience with Porsche, I do not believe in bad programming. Besides, the car was rolling roaded a few months ago at Sportec and I am sure they would not release the car if they had encountered the problems I had, in fact, they told me exactly this thing when I told them about the problem. They said that I should have the car examined immediately. The fact that I can still drive it in normal conditions (I drive it daily, today I reved it above 4000 in 3rd without any problems), they said, might indicate there is nothing very serious with it, but they have to investigate. Maybe bad pipes, maybe butterfly valve, who knows. Anyway, I drove it back from Germany, another 180 miles of unlimited track and I gone up to 200-230kmh for extended periods of time, everything running just fine. I drive the car daily even now, it behaves just fine.

So, early Monday morning I am off to Sportec HQ.

Oh, the car has the basic mods - exhaust with 200cell cats and H&R springs. Air filter is stock. Sportec are not known for crazy, "squeeze-all-the-juices-out", tunes, they are quite conservative.

NoPasaran

Hi, Macster

Thanks for your extensive comments, as usual!

You know, when I got that smoke that is what I thought as well, engine cobwebs, because most of the time the car is driven in the city and never sees 4000rpm, it is fast enough already at 3200 or so. That is why I tried a couple of times more, but, even though I did not get any more smoke, the car was "pulled back", I thought maybe it is AWD doing some reshuffling, but I will find out only when Sportec checks the car out.