Sajan

Update:
New solenoids are behaving the same way when testing via PIWIS and when logging. So what I saw was "normal". Car drives the same.

So far I have wasted money on:
- different oil
- fuel injector cleaners
- coils, plugs
- diff throttle pedal
- camshaft solenoids
- PSM on/off trick
waving the white flag for now.

there are some thing on my mind I do want to try but at this point I have wasted a lot of time/effort/money on this..going to pass on these:
- valve lift solenoids
- throttle body
- HPFP

duxsi

Don't feel too bad, for many have tried but none have conquered..

Sajan

I need to drive a 911 from someone who claims to not have this issue. I NEED to know for myself there's a car out there that doesn't have this issue.

There's one major thing that we need to eliminate. The actual DME itself. But doing that doesn't seem very feasible or cost prohibitive.

Has anyone tried trading the car in to see if that fixes it. LOL..

ettenw

Another data point: A couple of days ago I turned on my ignition but didn't start the car. I then turned off stability management (PSM) and noted that there was not the usual message on the instrument panel saying PSM is off. I then turned it back on and started the car. I went for a half hour test drive and I think I didn't feel any stumbling. I'm not 100% sure because of the occasional bump in the road plus I'm undoubtedly hyper sensitive about the stumble. Today, I started the car normally, not doing anything with the PSM. Another half hour drive and no stumble. This is on a 2016 Cayman S, manual, so it's the 3.4 liter engine.

tmarino

THe one solution I have found that works is to keep the RPM's over 3K as these cars do want to run................this advice was from my dealers service manager who also runs a 911.

Sajan

any luck for you with PSM on/off?

Can anyone confirm (or even check if you have a scanning tool) if the N020 and N040 actual intake camshaft angle for bank 1 and 2 is supposed to be the same?
It's under the DME --> Camshaft adjustment section

duxsi

Haven't had the time to test again..
Will try all permutations this coming week.

IWOA911

Is the hesitation during smooth acceleration from 2500-3000 or are you romping on it? I have a fairly new to me 2013 w/x51 and will have to see if it occurs in that range?

Sajan

Here's my go to test scenario:
Get it warmed up.
Put it in Sport, Manual mode
5th gear, start at 1800-2000 rpm, cars probably at around 40mph...start giving an additional 25-50% throttle (try to keep this steady)..as the RPM starts climbing/speeds picking up...you should feel 2-3 stumbles/stutters. one around 2200...2500...2800..
you should feel it a quiver.

now if you were to go from standing still...you would feel this as more of a pause at those RPM ranges.

I am pretty much convinced (until proven wrong) it's a symptom of the variocam system. whether it's a flaw in the software, a dme hardware issue, wiring or one of the various components (sensors/solenoids)..we will never know.
Maybe one of the sensors is giving erratic info. Maybe one of the solenoids are lazy. I changed 2 solenoids but that didn't make a diff. I browsed through the threads on here and the other forum, no one has changed the camshaft sensors from my understanding and maybe for $25 a piece, it's worth a try.

The PSM off and on has been an interesting development. Unrelated? Coincidence? who knows.

Watson

Very insteresting logs. Can you remind me what are the actuators of the camshaft for : variable timing, right? intake or exhaust side?

Assuming the actuators of the camshafts are related to intake valve opening or exhaust valve closing events, it is very strange to see the solenoid actuator values vary so much (which may explain why stumble occurs).
You are sweeping a relatively small engine map area (2000 to 3000 rpm, 35% to 40% of maximum torque request) so I would assume the targets for all the valve opening and closing events should be relatively similar.

It might be a stretch - one thing coming to my mind is maybe a software strategy used by the DME to clean the camshaft actuators (to shear off any hard particules that could stuck the valves of the solenoid actuators) - that would from times to times go from 0% to 100% as a preventive cleaning.
A bit strange to me that such a strategy would be applied when torque request is not 0% (due to obvious driveability reason which is the stumble we are looking at) so I might be wrong.

Some guesses:
- Do we have a common point regarding all cars affected by the stumble, are they all above a certain mileage (30kmiles, 50kmiles)? I am wondering if the DME has a counter based on mileage to make this cleaning strategy more frequent above a certain mileage or as mileage increase...
- Or the DME has a model inside (not dependent on mileage) that "predicts" the "ageing" of the camshaft actuators and decides to launch these cleaning strategies more frequently. Which could explain why after a DME reset, no stumbles occur for a while : at the beginning after the reset, the DME thinks it is dealing with a brand new engine and then "learns" that the engine might need more cleaning (rightfully or not).
Unfortunately, I am just speculating, the 2 points above could be totally wrong. Hopefully, someone really knows well the Siemens ECU logic of the 9A1 N/A engine and can share their knowledge.

Watson

I agree it seems related to the valves operation of the engine. Do you mean valve timing or valve lifting (or both)?
- Flaw of the SW : has anyone flashed an ECU tune with a totally different SW (such as MOTEC, etc) than the factory Siemens SW and found out that the stumble disappeared? It could be quite easy to swap between softwares and prove it.
- DME HW issue : need to find a good car with same drivetrain as your car and need to swap DME between 2 cars. Problem will be how to pair the new/other DME with your car - can the pairing of a new DME into your car can be achieved with the PIWI?
- Wiring issue : need engine out and new engine harness, hopefully it is not the case but a visual inspection of the wiring going to the camshaft sensors would be good.
- Camshaft sensors : yes it is worth trying.

For the PSM off/on situation, doing an A-B-A multiple times on several cars to prove that it is the rootcause would be necessary, although I am not holding my breath.

Sajan

The ones from the log are the intake camshaft solenoids. They control timing. From my understanding the 991.2 and onwards don't use the same part. They use this.
Of course the DME needs to know where the camshaft is that's where the position sensor helps.

Then there's the 2 solenoids that control lift.
- I need to see what others have said about different tunes.
- DME swap will be a pain. I was thinking of picking up a spare DME off ebay to try coding via PIWIS.
- Ya wiring would be a major pain..
- I ordered the sensors and they will be here this week. Can't hurt at this point lol..

I replaced the timing solenoids. After I do the sensors, I will move onto the lift solenoids.

tmarino

Has anyone isolated this 'stumble' issue to particular variant of the 991.1? Do GTS cars with the X51 Powerkit exhibit the same behaviour? Do the GT3's have the same issue? I would assume these are running all different DME units as they are all different in engine internals, intake etc. but I could be wrong about that. Trying to rule out the previous comments about the issue being related to the DME and or factory programming. Does anyone know of a car(s) that may be equipped with and aftermarket custom DME that has this tuned out or is strictly related to emissions as many have surmised? Thoughts??

pfan

My 2013 S has been stumbling since day 1.

PSM off continues to work well.

Joec500

I am very curious about this stumble, I have a 2013 with over 100k miles and the only time I get a dip in power is when I lose traction and TC kicks in. Are there any videos posted that demonstrate this stumble?