tlaritz

Starting with this driving season, I have experience brief episodes of significant loss of power in my GT4RS when driven on the track. The power can be restored by coming off of the throttle and then getting back on the throttle.

Initially, I experience this problem when accelerating out of slow turns. But, the problem has progressed to occur mid-turn (with associated over steer) and even on long straights with constant full throttle and well away from any PDK shfits.

I have experience about 8 of these episodes over this driving season. Last year, there was no issue, when I drove during the full driving season.

There have been no indications or warning or error messages presented on the dash board. That is, no check engine light, no warnings or errors shown in the right pod, and no messages accessible thru the right instrument pod.

We've found no stored codes as a result of the dealer's scanner for codes 4 times. Twice we scanned at the dealership, a number of days after experiencing the power loss on track. Twice we have scanned the car at the track, without shutting the engine down between the power loss on track and scanning for codes. Thus, the dealer is at loss as to how to proceed to isolate the problem and remedy the situation.

Initially, the services guys questioned whether I might be left foot braking while on the throttle. I understand that many Porsche models will cut power under these conditions. My recollection and the Solo 2 data show that there was no braking during any of the power loss events. (In fact, I can't even invoke the power cut with left foot braking in my car, and I don't remember experiencing that power cut with left foot braking in my 981 GT4.)

Because the power loss can be restored by coming off and then on the throttle, I am not inclined to think this is a "limp mode" issue, with the car protecting itself from overheating. I understand that limp mode, at least in some cases, is indicated by a yellow warning indication in the right pod. And, ,in many cases, cycling engine power off/on is required to leave the limp mode state.

My anecdotal experience shows that the cooling system of the GT4RS is robust. Last July, at High Plans Raceway (altitude ~ 5000 feet), in the 90+ F afternoon, I ran two 25-minute sessions separated by 30 minutes. The engine ran fine, with coolant and oil temps in the low 250 F range, for the complete 50 minutes running out of a total of 80 minutes. There was not one stumble on the part of the engine or transmission. I was shocked when one service manager indicated that an issues with 4.0L engine cooling would require me to drive, forever going forward, a cool-down lap after every 2 hot laps.

There has been some concern that the DSC suspension controller I have installed might be a factor in these power loss episodes. I had no issues with the car in 2023 even though the DSC controller was installed for the entire season. I spoke to Tom at DSC, and he indicated that they have 5000 track miles, driven over 13 months, in their GT4RS with no power loss issues. Obviously, they have their suspension controller installed in their GT4RS.

The other non-Porsche part connected to the car is the Solo 2 DL v2 data logger. The dealer guys would like to rule that component out also. But, I have connected the Solo 2 DL via the Inventure CAN CL monitor (see: https://www.inventure-automotive.com...cts/can-sensor). This device allows for monitoring of the CAN bus without making electrical contact with the CAN bus wires. And, the device prevents anything the Solo 2 might transmit from being forwarded to the car's CAN bus. Further, I also had the Solo 2 DL installed my car for the entire 2023 driving season.

(Note: We have swapped out the DSC controller for the Porsche controller and disconnected the Solo 2 from the car to see if the problem persists. I'm off to Pueblo MSP this weekend for a DE.)

When accelerating from turns, the power loss has occurred after both left and right turns. And, fuel levels have been sufficient for all episodes.

The current mileage on the car is 12500 miles. I drove 20 track days last year, and about 12 track days this year.

On track, I always have sport mode enabled for the transmission, and almost never shift manually via paddles.

I'm sure that I have forgotten some major detail, so please do ask questions.

Shortly, I will be posting plots of the Solo 2 data for 4 power loss episodes.

Thanks

GrantG

Could it be traction control intervening? If you get wheel-spin on corner exit (or anywhere else), it will cut power to prevent this. BTW, maybe we met at HPR recently? Hope to see you there

You could turn off TC to see if this helps (just be prepared for a little oversteer).

Alan C.

I believe he indicated experiencing it on straights as well.

sdillon

Not trying to be Captain Obvious and this is probably a silly response, so disregard if you agree, but - the only similar experience I've had in mine was when I ran the fuel too low at the end of a session and momentarily starved the motor. I'm not suggesting you did that, but only mention it as something to look into - like perhaps your car has a fueling issue somehow / somewhere. Once when I did that my car threw a code, the second time at RA last weekend it was *very* momentary and there was no code.

Mine has been rock solid, and I have not experienced anything remotely close to a cooling issue, either. About 20 track days so far. Stock motor and drivetrain.

tlaritz

I've generated a series of plots of Solo 2 data, giving them to the service guys, in an attempt to help in diagnosing the problem. I generated the plots in Matlab vs RaceStudio. It was very difficult for me to generate a consistent set of plots, over the various power loss episodes, using RaceStudio. The plots below are what I call summary plots, with one page with 6 plots per episode. Soon, I will be posting added plots with more detailed data.

Attached is the first summary plot for power loss coming out of T5 at La Junta. All plots use lap distance as the x axis. The blue vertical cursor indicates the start of the power loss. On each plot, data from two laps are shown: a black, baseline lap with no power loss issue, and a red lap, which is the lap with power loss. For all plots, ~1000 feet of lap distances is represented across the x-axis.

The top most plot shows throttle position, in per cent. For the red lap, I lifted and got back on the throttle (at about 3400 ft),, which restored power, which is shown in the second plot.

The second plot shows a value TRQ_WO_MEC. It is one of about 8 torque values which the Solo 2 records for the Cayman platforms. Note in the red lap this torque value goes to 0 at the blue vertical cursor even though the top plot shows the throttle at 100%.

The next plot is engine RPM. Note how the engine RPM decreases (in the red lap) starting at the blue cursor until about 3400 lap distance. This is concurrent with the period where TRQ_WO_MEC is 0. It looks like (see below) the car initiated a PDK shift, starting at the blue cursor. (See below.) This shift was "short" occuring at ~ 8k RPM vs closer to the 9L redline.

The next plot is an unreliable indication of transmission gear. The ECU profile in the AIM Solo 2 did not correctly decode transmission gear for this PDK transmission. (This profile issue has just been resolved.) Not much can be inferred from this plot.

The next plot is the compute transmission ratio which I calculated. Is is calculated as 0.01911 * engine RPM / vehicle speed. (The .01911 takes into account units, final drive ratio, and tire diameter.) Porsche states the ratio for the GT4RS are:

1st: 3.75
2nd: 2.38
3rd: 1.72
4th: 1.34
5th: 1.11
6th: 0.96
7th: 0.84

During most of the plot in the red lap, the transmission ratio is ~2.5 (2nd gear) or ~1.5 (4th gear). Starting at the blue cursor, there is an extended period, of about 0.5 seconds, where the transmission is between gears. One thought is that the PDK is trying to simultaneously engage 2 gears. Another is that one or both of the PDK clutches are slipping. At around 3000 ft on the x-axis, there is another period of time where the computed transmission ratio (in the red lap) is between the values in the table above.

The final plot shows vehicle speed. Of course, the speed for the red lap is lower than the speed of the black lap starting at the cursor where power is lost.
I forgot to say above that the car has about 12500 miles on the odometer today (9/6/2024). At ~11000 miles, we changed the transmission fluid and filters, and sent fluid samples to Blackstone labs for analysis. Those reports are attached. Blackstones's analysis said that the values were consistent for a transmission of this age.

I will post more summary plots soon.

Thanks.

tlaritz

Yes, TC intervention is a good point. And I have yet to find the bit indicating traction control intervention in the CAN bus data stream for logging in the Solo 2. (If anyone knows the message and bit value for TC intervention, I'd love to have it.)

In the past, the TC intervention I've experience has been much more subtle--ie, engine power is not reduced to zero.

One of the forth coming episodes occurred mid-turn (HPR T12) and the power reduction was so great that oversteer resulted. If that was TC intervention, then it's "cure" did much more damage than good.

And, as pointed out, another of the forthcoming episodes occurred during the HPR highway straight, in 4th gear, at speed. The wheels speeds showed no slipping. I'm reluctant to think that TC intervened here.

But I will continue to consider TC intervention.

Thanks.

PS I have started also collecting data with the Track Precision app. It records TC intervention, which will be helpful going forward.

At this point, no question is a bad question. Please ask questions whatever they might be.

GrantG

That is curious, but it is possible to have wheelspin even when going straight (particuarly when tires are worn and track surface is less than ideal).

tlaritz

Yes, fuel starvation has been discussed. For the four episode I'm documenting here, the fuel level has been above 13 gallons. So, I would discount fuel starvation at this point.

Another important detail: When exiting a turn, the power loss has occurred coming out of both right (ie, HPR T6) and left turns (La Junta, T5).

I'm less inclined to think that oil starvation is at play here, given the design of the car's lubrication system.

tlaritz

The wheel speeds of the rear wheels (WHEEL_RR and WHEEL_RL in Solo 2 parlance) did not show wheel slippage during the power loss episode on the long straight.

GrantG

It’s not oil starvation. Not only because of dry sump, but you would have a low oil pressure code stored as well.

mwar99

Maybe not fuel starvation because of fuel level, but maybe a fuel pump, injector, filter type issue? The fuel could be "starved" in other ways potentially.

tlaritz

Attached are the summary plots of a loss of power when accelerating out of T6 at HPR, a right hand turn. The black line is for a baseline lap without power loss, and the red line represents the lap with the loss of power.

These plots are in the same format as those shown for episode 1. Again, the vertical blue cursor is located at the beginning of the loss of power as seen in the TRQ_WO_MEC plot.

In the red lap, the engine RPM was 8370 and the throttle at 100% when power was lost. In the black lap, the 2-3 upshift occurred at 8900 RPM, much closer to redline. (Note that there is a brief decrease in torque during upshifts, I assume for rev matching.)

Based on transmission ratio in the red plot, the shift from 2nd (ratio of 2.38) to 3rd (ratio 1.72) took about 0.5 seconds. In the black plot, the 2-3 shift required just over 0.1 seconds. In the red plot, the transmission immediately did a 3 to 4 (ratio 1.34) shift and never downshifted again after the throttle returned to 100%.

I know this is a lot of detail, but I don't know how to better proceed. I'm trying to show the added details in layers, one layer at a time.

Thanks

tlaritz

Good questions about alternative ways which fuel starvation can occur.

Does anyone know if a fuel pump, injector, or filter issue would result in a stored code?

If not, I'd have to ask my dealer service guys about these alternatives.

tlaritz

One more comment about fuel starvation in addition to my response elsewhere.

There seem to be symptoms in both the engine and transmission data. But because the engine and transmission work closely together to perform shifts (for example), I am reluctant to say that symptoms in the transmission plots exonerate the engine, or visa versa. Thus, I'm hesitant to point to transmission "abnormalities" to rule out engine fuel starvation. (This is a subtle point. But, I don't think I'd be in my situation if the problem was simple to solve.)

So, I'm agreeing that I should investigate other ways fuel starvation can occur.

Thanks.

bantam1

I would not be investigating how, but rather, if you have fuel starvation.

the way that I would do that is to datalog fuel rail pressure.