I got my car dyno tuned by a well known professional about a month ago. Since then the car drives sooo much smoother. The only thing is, when I shift, or when I let off the gas to engine break, it will pop, and seem to backfire. The engine doesn't hesitate or anything. The tuner said it may be the fuel cut options in Neptune RTP. I have tried fiddling with almost every option and it does not seem to get rid of it. I just had a friend behind me driving that saw my exhaust when it pops. It blows out black smoke. Any ideas will be appreciated. I actually have an hour long datalog session, if anyone would like to see it. Though, it won't have marks for where the pop occurs.

 

Your tuner is correct... Decel fuel cut settings need to be looked at.

 

Are there any suggestions you might have? Right now, parameters are at:
Below load: 249
Below TPS: 1%
Min RPM: 1900
Min Speed: 0
Cut Delay: Id say is about 40% of the bar.
Would it be unsafe to set the min rpm to 1300? If I drop min rpm to 1, would it not idle?

 

Do you have any exhaust leaks because I had the same problem when I knocked a flange loose.

 

It is possible there is a slight exhaust leak, he had recommended that as a possibility while we took it on a part throttle tuning run. Though only place possible would be where the headers connect to the cat, and the new donut gasket isn't sealing. The reason I considered that option ruled out is because I am using the same exhaust I had for my D15 that was in my hatch. The only difference being a hollow cat. It never popped with the D15, and it didn't pop when I swapped the motor and drove it for 2K miles before I got it tuned. As soon as he tuned it, that was happening. But I will definitely check for exhaust leaks today when I get under the car.

 

That damn donut flange is what is causing mine. No matter what I do I cant get it to seal up very well. I even added a few washers on the spring side for a little bit more clamping force and it helped but not completely.

 

I woundnt set the min rpm any lower than about 1600. Make sure your TPS is reading true 0% in the logs when at closed throttle.

 

Thanks, the TPS reads -1% when closed on Neptune RTP when datalogging. What does that indicate?