Re: Slight hesitation or miss when cold - opinions?

I am having an intermittent issue with my 2009 C2S Coupe approx 30K miles. I thought I would post this here as the expertise appears very high. Pedro has done a good job with this forum.

Odd, I get a miss when accelerating slightly when the engine is cold. It appears to be around 3200 RPM but I am not sure it is dependent on RPM. No lights.... no other symptoms.

Do misses register in the computer? Any ideas or anything I can check myself? I have an OBD2 reader but I haven't popped in on yet.

By the way, I have not found a quality forum for 997.2 cars..... any one recommend one?

Peace
Bruce in Philly

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Bruce In Philly (2000 S Boxster, now '09 C2S)
I am having an intermittent issue with my 2009 C2S Coupe approx 30K miles. I thought I would post this here as the expertise appears very high. Pedro has done a good job with this forum.

Odd, I get a miss when accelerating slightly when the engine is cold. It appears to be around 3200 RPM but I am not sure it is dependent on RPM. No lights.... no other symptoms.

Do misses register in the computer? Any ideas or anything I can check myself? I have an OBD2 reader but I haven't popped in on yet.

By the way, I have not found a quality forum for 997.2 cars..... any one recommend one?

Peace
Bruce in Philly

It would appear to be then a hesitation.

With no CEL and thus no error codes there's not much you can do...

Well, there are a few things. Check for pending DTCs.

You can monitor intake air temp and coolant temp before, during, and after the hesitation event to see if one or both varies in a way that might explain the hesitation. I am thinking perhaps of an intermittent failure of one sensor which momentarily causes the DME to have to adapt or attempt to adapt to a sudden change in temperature. Ideally, if the test tool supports it, you should also monitor the short term fuel trims looking for some sudden but brief change in the fueling. Oh what the heck, while you're at it monitor ignition advance too.

I'm thinking the behavior you report could be an early warning sign of pending fuel pump trouble.

Anything done to the car recently? Add an aftermarket CAI perhaps? Change a fuel filter? Plugs?

was acting up, on its way out.

I'm not current on the newer cars, whether these have a weak AOS.

You're not running some goofy oil viscosity in the engine are you?

What is the spark plug change interval for your car? 30K miles is a bit early imho for NA engines though of course if the book calls for a change.. I'm there.

But I would not recommend a plug change otherwise, at least not yet.

Let's see 2009... that's the DFI engine. One possible explanation is valve and engine chamber deposit build up. With DFI there is no cleaning spray of fuel hitting the back side of the intake valves. This area can accumulate deposits as there is some flow of exhaust gases into the intake under some operating conditions. This is normal.

But the result is the valves can build up deposits which interfere with the air flow into the chambers. These DFI engines are highly sensitive to anything that interferes with the with the air flow into the chamber.

Engines of cars that are driven more sedately are more likely to develop these deposits since the engine operates in the rpm range at which some back flow of exhaust into the intake at least as far as the valves are occurs.

Thus you might consider using Techron a bottle or two as per directions to help remove any deposits.

If at any time the hesitation becomes more severe or there appears any other abnormal behavior shut off the engine first ask questions later. I do not believe anything serious is wrong or will go wrong this is just my usual CMA advice.

Which brings me to another bit of CMA: Obviously I'm not at the car and I do not know how serious the hesitation is. You might, in fact you probably should have this checked out by a qualified tech just be sure there's nothing serious going on. Actually any hesitation is serious as it is clear the engine is not operating as it should and this is always cause for concern.

I doubt it would be the fuel pump since the hesitation only happens while the engine is warming up and not after it's a operating temperature.

first hand the behavior there is the possibility an Italian tuneup is the wrong thing to advise.

But often I hear from the techs that someone brings in a vehicle with some sort of vague not running right/or at its best complaint and that is just what is recommended. Take the vehicle out and drive it harder.

RennTech.org is an excellent source for technical information. As far as a social site goes.........it's difficult to beat Pedro's Board.

Bill

... the MAF is causing the hesitation.
If it's only happening when cold I can almost assure you it's the MAF.
You could clean it and see if it helps.
Happy Boxstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

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Edited 1 time(s). Last edit at 05/09/2013 06:11PM by Pedro (Weston, FL). (view changes)

Pedro, I will do the MAF cleaning this week. I need to look at the air filters anyway as I was in and out of seriously filthy dusty places lately and wanted to check them anyway.

Another question: Can I bang these air filters on the ground and get some more life out of them like we did in the "old days"?

Regarding the hesitation, I found quite a few folks who have this issue from 997.1 to 991 and it appears to be, fundamentally, a variocam issue. But not always noticeable in all cars - this is really odd to me. From a poster in another forum:

"I had this on my 997.1 and notice it on my 991 C4S which I have had for two weeks. It is very noticeable to me, slightly more when cold.

On my 997.1, I took it to the dealer a few times and they said it was the variable cam adjustment that takes place at around 2,800/2,900 RPMs. The reason I took it in more than once is I couldn't believe it was that noticeable and was convinced it was a defect with the engine, eventually accepting their explanation. I had hoped it would be improved on my 991 but after driving it, I think it is about the same.

I'm a little surprised that Porsche hasn't done a better job with their variable cam system. I accept it as a somewhat weak feature of an otherwise great car."

So, we will see after I clean the MAF. But I am thinking, it just may be part of the wonderful charm of variocam.

Peace
Bruce in Philly

At about 3000 RPM the car seems to stumble a bit which coincides with a dip in the engine torque curve; there is no such drop on the 991 but a substantial one on the 981. Click on the technical spec footnote on the HP rating and the HP/TQ curve will show up.

[www.porsche.com]

It peaks around 2500 and falls off to 3500 rpm, then recovers to the torque at the 2500 rpm level at about 4000 rpm.

The torque curve on the 991 seems to be a steady rising curving by comparison.



Edited 1 time(s). Last edit at 05/12/2013 10:39PM by MikenOH. (view changes)

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Boxsterra
n/t

That sounds about right on the 981S.

Regarding the 991/981S 3.4L comparison, if you look at the 3.4L 991 torque/HP curve, you can see Porsche did things differently on that motor vs. the 981S--smooth torque curve vs. drop off, providing 20+ ft.lb of TQ and 35+HP.
Different induction system, larger exhaust header? Sure doesn't look like an ECU tweek.

At a quarter mile from my house the cross street goes uphill for a hundred yards or so and there's what feels like a subtle washboard surface for a couple seconds. Keep in mind some hilly roads develop a bit of a washboard as the asphalt is pushed around. Many heavily traveled intersections develop this, too, from what I suppose is the frequency of braking. Subsequently, I've observed the effect during level, cold start travel. Within a few months of getting the car I questioned the dealer about this, and if I recall, they said it was a characteristic of it being DFI. It could be, too, that I sometimes have a "nervous" foot and I'm unintentionally feathering the throttle somewhat. Again, let me stress in my case the effect is nothing like a miss or hesitation; more like a vibration if anything, and nowhere near as apparent as the classic 3k rpm vibration many earlier motors have.

I think the hill is the mild load or slight acceleration where it shows up. I will report back when I go to the dealer in a few weeks.....

Bruce in Philly