i noticed last night around 2 30 am when i was doing some hard 4th gear pulls on the highway, when i let off the throttle i could see 2 very large orange flame flashes light up the sky behind the car. Now i cant actually see the flames, but i can tell they must be quite large as they are quite bright and pronounced. Flames dont bother me at all, but the idea that maybe they are huge and could melt my bumper on fire or something is a slight concern, as well as the idea that maybe there is too much fuel on decel which could build up carbon, foul plugs, run high egt's, and contaminate my oil quicker (i can smell fuel on my dipstick)

My question is how do i tune this? if i remove fuel from the highest vacuum spot P1 would that help? would there be any drawbacks to this? I saw one map out of probably a dozen that had very low MS in the highest vacuum portion. When i say low it was like 0.024 or something like that. When i saw it i thought well thats strange, then later i started thinking... really why do we even need fuel in that portion of the map? and does it have any effect on deceleration? I would think on decel the injectors would just go to zero anyway, but that's the only time i have ever noticed being in that part of the map is when my foot is off the pedal. Comments?

 

First, what are your 3 Fuel Cut ( F/C ) values set at?

 

1400 for all 3

 

When you let off the throttle, it takes a little time for the injectors to turn off.
Attached is one of my 16 psi runs starting about 3200 rpm then letting off the throttle at 7200 rpm. I am using 20ms of Hold Off on Match Watch.

Look how long it took the AFRs to drop. That was 1.702 seconds on the log for the AFRs to drop down to 19.9 (air). If you look at your cruise tuning logs, you only use P1 - P5 up to about N5. Never use P1 - P7 above about N8. In reality you could put 0 ms in the areas only used for off throttle.

 

I suppose there would be no advantage to running 0 ms in those off throttle areas as the ecu shouldn't be sending any pulses anyway. So i'm guessing there is no way to reduce the amount of off throttle fuel being dumped into the exhaust then?

 

My example is the only one I had to show. I shifted to neutral as I lifted the throttle. That is why the revs went up. Fuel cut would have been faster if I lifted the throttle first than shifted to neutral almost like I was braking for a corner.

Since your fuel cut rpm is low, the 3 ways to reduce afterburn are:
(1) make sure that your boost AFRS are not overly rich.
(2) lean out any cells not used for driving that the revs would fall though when getting off boost throttle.
(3) lean out used cells for lower boost setting and cruise.