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I have already posted this good news on 6Speed but wanted to bring the members here up to speed too (pun intended. And although my car is completely stumble/hesitation free, my good fortune may or may not be the fix for others, though I find it mathematically unusual that there's more than one "issue"! With out rehashing every little detail I will breifly review what/where/when of my issue. I have posted regarding this since February. I liked my car and it's build/colors so much that I decided to have the X-51 kit installed in my 2013 C4s rather than the highly recommended option of selling it and finding a GTS4 cab. My dealer's most experienced technician (mechanic) did the install over a 2 week period in December 2016. He had very few "issues" and it went fairly smoothly. He had to replace one injector as one broke removing it and the kit did not come with new head bolts and he wanted them as well. I did the modification under the Porsche maximum recommended mileage of 25,000 miles (23,500) and after the required "break in" mileage of 500 miles, I discovered a very noticeable and unpleasant stumble around 3k rpm. Not always, not predictable, but frequently. And it was very annoying and disappointing to be sure. I had no such issue before the mod. I took the car back a total of 3 times, the last one being the charm. The dealer had the car for 2 full weeks and the mechanic (same one who installed the kit) found the "problem". At least for my car. See below, a copy of the service order. It is absolutely fixed! It drives so amazing now. The X-51 was awesome before if I put my foot in it, never stumbling under heavy throttle input, but under medium load, it would rear it's ugly head more than I could take. Especially after spending over $16k! The X-51 engine revs quicker to redline and the intake sound is intoxicating and throaty. I am very happy to have this outcome, and a bit surprised as I had just about lost hope from reading the huge thread on 6Speed. I hope others can get their's figured out. My car is fantastic now. I have had it back a week tomorrow and keep driving the hell out of it with a big smile on my face. So happy, so thankful.
There are many people reporting a stumble without an X51 install, so while happy your problem is fixed, seemingly caused by an improper installation, not sure how it will help those that have a stock (un modified) car with the problem.
There are many people reporting a stumble without an X51 install, so while happy your problem is fixed, seemingly caused by an improper installation, not sure how it will help those that have a stock (un modified) car with the problem.
Just maybe their cars came from the factory with the same connection issue! I do not have PSE, but evidently our cars are "wired" for it, base, S, 4s, manual. PDK, doesn't matter.
Lucky that warranty covered the labor since the aftermarket exhaust caused it! Unless the dealer put that on too... which would be their mistake
Did you read the fix? Sharkwerks Exhaust had absolutely nothing to do with the stumble! Had it on the car for over 2 years and 10k miles with NO ISSUES! The mechanic actually said that it would be a better exhaust with the X-51 than stock including PSE!
Never had the stumble on mine, but it's had the X51 on it from new. Strange the PSE connection would have anything to do with it.
The tech said the "connections" look identical! But would infact effect the car by not sending a signal to retard or advance the ignition/timing for the vario-cam, which caused the stumble! More to do with the coolant valve control than the PSE. Again, I do not have PSE but it is "pre-wired" from the factory. All I know is what he said and wrote AND the car is PERFECT!
Side question - what does Porsche charge for X51 parts/labor on a "used" 991?
X-51 kit from Suncoast was $9250 delivered to my dealer (no tax), and the install was a winter time contract of $6k. It cost a bit more as an injector and head bolts had to be ordered. Total was just over $16k. I already had SC. I did not get the PSE version. It did come with center radiator, heads, intake cams, and new 6 + 1 switchable intake. I also had installed the Rennline screen protector while the bumper was off.
Does anyone know where the PSE and engine coolant shutoff control valve connections are physically on the engine? I would like to be able to visually inspect.
05-21-2017, 10:37 PM
Stumble is fixed
. And although my car is completely stumble/hesitation free, my good fortune may or may not be the fix for others, though I find it mathematically unusual that there's more than one "issue"! With out rehashing every little detail I will breifly review what/where/when of my issue. I have posted regarding this since February. I liked my car and it's build/colors so much that I decided to have the X-51 kit installed in my 2013 C4s rather than the highly recommended option of selling it and finding a GTS4 cab. My dealer's most experienced technician (mechanic) did the install over a 2 week period in December 2016. He had very few "issues" and it went fairly smoothly. He had to replace one injector as one broke removing it and the kit did not come with new head bolts and he wanted them as well. I did the modification under the Porsche maximum recommended mileage of 25,000 miles (23,500) and after the required "break in" mileage of 500 miles, I discovered a very noticeable and unpleasant stumble around 3k rpm. Not always, not predictable, but frequently. And it was very annoying and disappointing to be sure. I had no such issue before the mod. I took the car back a total of 3 times, the last one being the charm. The dealer had the car for 2 full weeks and the mechanic (same one who installed the kit) found the "problem". At least for my car. See below, a copy of the service order. It is absolutely fixed! It drives so amazing now. The X-51 was awesome before if I put my foot in it, never stumbling under heavy throttle input, but under medium load, it would rear it's ugly head more than I could take. Especially after spending over $16k! The X-51 engine revs quicker to redline and the intake sound is intoxicating and throaty. I am very happy to have this outcome, and a bit surprised as I had just about lost hope from reading the huge thread on 6Speed. I hope others can get their's figured out. My car is fantastic now. I have had it back a week tomorrow and keep driving the hell out of it with a big smile on my face. So happy, so thankful. 
