Nate Tempest

So I noticed the past couple days that when doing second gear pulls, I sometimes feel the car hesitate (not pull as hard) between around 4k and 5k. Turbo comes on strong right after shift from 1st gear, up to ~4k, then seems to back off a bit, then pulls hard again from 5k to redline.

It doesn't happen in first gear, and it seems to only happen for the first one or two pulls in second, then not anymore. Happened like that both days. Car well warmed up from regular driving; wasn't cold for these.

Any ideas what could be causing this?

bondjockey

Does it have a tune? If so I would datalog your car and start there.

Nate Tempest

I had that thought, but no, I don't have a tune (yet) unfortunately. Maybe this is an excuse to get one...

Still holding out hope though that someone's going to reply with, "Yes! I had exactly that symptom, and the cause was _____."

IMI A

Coil pack or sticking turbo actuator rod?

Macster

No CEL? No pending codes?

Sort of reads like given what you wrote the engine's intake -- and this includes the intercoolers -- experienced a bit of heat soak and under hard acceleration the DME had to back off timing possibly boost because of this.

Is the gas fresh? The right octane grade? Is the engine in good tune? Engine air filter good? (Don't laugh. I just replaced the engine air filter on my Boxster -- the filter was clearly past the point it should have been changed -- and the engine is running remarkably better.)

How old are the plugs? Not saying you should throw parts at the behavior but with Turbos the plugs, air filter, fuel filter, O2 sensors, are all even more critical than with other N/A models.

With my 996 Turbo I replaced all 4 O2 sensors when one manifested an error code (bad heater). Afterwards the engine ran better.

Then more recently I had the tech replace the coils along with the plugs -- the plugs had around 10K more miles to go before they were due but the tech advised replacing them at the smae time as the coils -- and the engine ran better afterwards. I've had the plugs replaced before with no improvement from the engine so the improvement was I think due to the coils.

The behavior you experienced could be due to just a Turbo engine in need of a "tune" that is a refresh of wear items that play a vital role in how well the engine runs.

Nate Tempest

It wasn't particularly hot out when this happened, and it was for the first couple attempts, then it got better (when the engine would've been hotter if anything). No CEL. Not sure about pending codes.

Air and fuel filters were changed in November. It is almost due for its 8 year spark plug change, so that might be worth doing regardless. I believe it's on its original coils, but normally those should last a long time.. (They're not even listed in the maintenance schedule.)

So, since I need to change the plugs anyway, might as well do that and see if it solves the problem, then go from there. Just need to see if it makes sense to change the coils at the same time.

ble2011

I thought most issues relating to the engine not running its best is related more to coils instead of plugs?

Nate Tempest

Honestly if it were plugs OR coils it seems weird to me that it would only manifest in this very specific situation. Idle is rock steady. Something like an O2 sensor feels like a better fit. But I'm no mechanic.

JG 996T

Add O2 to your while you're in there. Sounds like car needs a tune up (plugs coils O2s)

I have UMW tuner on the way.

Nate Tempest

Since O2 sensors are easily accessible, wouldn't it make sense to do plugs/coils first, and see if problems are solved? No need to replace working parts unless they're hard to get at, right?

JG 996T

Maintenance item. Just widebands. But you're right easy access.

Macster

The engine would not have been that much hotter. The cooling system sees to that.

During these runs the intake system loses some heat soak though but if the car is stopped can rather quickly regain the heat soak. (My 996 Turbo has a 2nd engine compartment fan fuse that when installed keeps the engine compartment fan running all the time the engine is running and this tends to keep the engine compartment cooler during slow driving and when stopped for a light.)

The intake can get quite warm from heat soak and it can take some time at speed to remove this heat. In the meantime the heat can affect the engine's performance.

There is the issue too of the DME and its learned adaptations. At the strip generally the 1st run is for the "DME" to get it to unlearn what it has learned under more sedate usage. This is more a myth than real as the DME constantly adjusts to inputs to deliver the torque requested by the driver yet maintain safe engine operating conditions (and clean engine operating conditions) at all times.

Still if the engine has not be pushed hard at all for a while the 1st run or two can blow some cobwebs out. Sometimes when in my Turbo I get someone who wants to "race" me. The car will be ahead of me and we are entering the freeway and the driver of the car ahead will floor the accelerator. Often this is probably the first time the engine has been unleashed in months of driving and the engine emits some visible exhaust. "Cobwebs."

Granted coils are not a scheduled maintenance item. They do degrade though as I learned from my experience after having the original ones replaced albeit at around 140K miles.

For both my Boxster and my Turbo when I've talked to the tech about coils his recommendation is absent any CEL that can be caused by a coil as long as the coils do not show any signs of any cracking or other signs of deterioration to leave them alone. He did say these should be handled with care. It is not nice to coils to just toss them around against each other.

'course, if the engine is down a bit on power and there are no clear indications of what the problem is then coils have to be suspect.

When you have the plugs changed talk to your tech about replacing the coils if you want. At plug change time if you want to replace the coils that is the best time. While the cost of the coils is not that much the labor can be a bit on the high side and changing the coils at the same time as the plugs saves some money in labor and that's a plus.

IMI A

Any news on this OP?

Nate Tempest

Not yet. I'm doing a clutch job (with BBI slave upgrade, woo!) at the same time, so just collecting parts right now. Went ahead and ordered a Cobb AP from Sam @ bydesign at the same time, so I can do some data logging (and then a tune - woo again!)

MadScience

Try graphing the O2 sensor data. Even a generic code reader/phone app will do that, since it's part of the emissions data. If it's slow to react, change it.

Also, a full set of bosch sensors for the 997.1tt is like $350, hardly a big deal.