I figured I throw this out there just to collect suggestions on how to solve this problem with my CS. I am experiencing misfires/stumbling above 7k RPM especially in 3rd gear (or higher). The car is not throwing codes (I assume) or going into limp mode. I do not have official scan results yet from my shop from the latest occurrence. Does anyone have any similar experience or suggestion on what might cause this and how to resolve?

Here is a short video of the issue. The problem happens at about 0:15. I got off the throttle quickly to prevent further issues.


Some background... I have been struggling with this issue all year. I had the coils and plugs replaced but it made no difference. It had been getting progressively worse and we thought we finally solved it when we discovered that one catalytic converter was bad. Last week I had them swapped out for race headers and was hoping this was going to be the solution. The car is otherwise stock. Previously the car would lose power above 6k and experience misfires as RPM's rose especially with higher temps/heat soak. In the first session out this weekend with headers, the car felt great and pulled hard right to 7k RPM but then eventually misfired in 3rd with WOT above 7k. I only did a couple laps to get things up to temp and this was the first WOT run on the straight.

Any input or past experiences would be appreciated. I will have my shop take another stab at it but it would be nice to have some proven solutions to put us on the right path. I am thinking it might be fuel delivery related but have no evidence yet.

Here is the VBOX data screenshot from that session with a marker on the RPM where the misfiring was occurring.

 

Fuel cell or plastic tank?

Might be the foam deteriorating and clogging the fuel system/ injectors.

 

I agree with Yannick, check the fuel pump for foam debris. Ran into this on a GT4 MR late last year.

 

Fuel cell... I'll put this at the top of our list to inspect. Thanks guys.

 

Demonspeed now has replacement foam for for like $900.

if you have data logging, you should be able to see if the fuel pressure is dropping as the problem arises.

one other thing to check is the fuel connections in the cell. If you don’t click the plastic line in all the way, you’ll get this symptom (ask me how I know).

 

The plot thickens. The scan came back with one fault: "1530 fault – implausible camshaft signal"

I am leaning toward cam sensor now.

 

While i have no experience with this model u may also need to inspect the tone ring on the flywheel too.

 

As an update, I had both cam position sensors replace and ran the car on Sunday. It performed perfectly for 3 sessions in the morning. Then, the first session after lunch, the issue came back after just one lap. I brought the car in and had it scanned with PIWIS but unfortunately there were no codes this time. The issue seems like it might be aggravated by higher ambient temps. Historically it has popped up in afternoon session, not morning. This day it was 70's in the morning and 80's in the afternoon so not super hot but hotter.

@38D unfortunately I have data but it is VBOX and my car does not have a gateway so I don't think there is any way to get the important engine parameters logged. I emailed Racelogic and got their newest/best reference file but it does not include what I need. I am thinking about installing a Cobb on the car just to get comprehensive engine data logs. Eventually I will load a tune but for now this seems like the best way for me to log.

@coryf @Yannick-HST if the issue was foam deterioration and fuel restriction, would the symptoms be so intermittent or temperature related?

@De Jeeper My shop also mentioned flywheel as a service item and I don't know the service history on mine so it is on my list. Could the symptoms match and/or be temperature related?

 

Have you replaced the fuel pump relay in the front trunk?

 

<duplicate>

 

Sorry dont know. I just wanted to through it out as a possibility. I would persue the fuel delivery issies first.

 

When we had the problem, the car would run well for a few laps then start the missfire. It was also cornering load sensetive probably from the debris sloshing around with the fuel. It's very simple to check. Randomly we had the same code for a bad cam position sensor which did not fix ours either. The code was probably not related but just a potential common separate issue with the cars as they reach a certain age.

 

Thanks everyone for the continued support with this. I feel blind with this intermittent issue and no codes so these past experiences are super helpful! The other problem is that my normal shop is booked for August and travelling to support races so I am working with a shop that is capable but less experienced. I am doing a lot of my own legwork to expedite a solution and salvage the remaining track season.

@coryf This really sounds like my issue. I am going to focus 100% on this. Thanks for the further details!

 

I had a very similar problem 2 years ago shortly after I got my 981 Clubsport. Car would run fine in the lower gears, then would break up in 4th gear well below redline. That was the last track day of 2021.

My car would not start in spring 2022. The fuel cell foam had disintegrated. Low pressure pump in cell was completely clogged and high pressure pump on engine wasn’t much better.

The previous owner had let the car sit with very little fuel - which I found out later. It would have been easier, quicker, cheaper and less frustrating to just replace the foam when I bought the car. Live and learn. This after replacing the coils, fuel pump relay, cam sensors.

The shop I work with told me last week they have recently replaced the foam in a few other Clubsports with the same symptoms.

Good luck, Hope you find the root cause soon.

 

No direct experience here, but as an interested enthusiast, I wonder if fuel level could have also been a factor. Did you refuel between morning and afternoon sessions when it showed up last time? A lower fuel level causing the problem to return could point back to the fuel system as the issue - there would be lower pressure at the pump pickup point due to lower fuel level. This could then result in a fuel pump that has started clogging up not being able to keep up.