Stutter/Hesitation when going to full throttle

[K24Miata]

Hi all,

I have a K24A2 powered Mazda Miata running Hondata Kpro V4 on an 03 RSX ECU. The car has been running really well for the most part, however at autocross we've been having a weird problem where the engine stutters or hesitates when going to full throttle on corner exit (you can see it on the image below).



It almost sounds like the car is running into a rev limiter or traction control (which the car doesn't have). Weirdly, it doesn't seem to have this issue when accelerating in a straight line, only when coming out of a hard corner. The car was run at a track day a few weeks ago and didn't seem to have any issues, but it was cold and slick so we were taking it a bit easy. The only difference between the track day and the autocross is we added a supertrapp muffler to the exhaust at autocross because of the sound limits at our site. The problem also seems to be worse the warmer the car is (i.e. first couple of runs, not as bad, worse on subsequent runs).

I've attached a data log with the problem. I can't figure out what it could be, everything looks pretty normal. It's definitely not fuel pressure dropping, as I also have a AIM Evo3 system in the car logging fuel pressure.

Any thoughts are appreciated!

[Hondata]

My first thought is that you're falling out of VTEC due to lack of oil pressure.

Something is odd with the lambda. It is not going lean on overrun. If it is accurate, then you're running really rich at WOT - 11.2:1 whereas it should be 13.0-13.2:1

Anyhow, the stumble is because the injector is going from 13ms to 10ms. So your fuel needs tuning. See the point above.

I'd also get the speed input working.

[K24Miata]

Thanks for the input.

Could it be that the rich condition is being caused by the flow restriction of the supertrapp muffler we added after the car was tuned (it is running open loop)? I will pull the muffler and do some more test pulls to see if that corrects the AFR issues you identified.

Oil pressure logged on our AIM system shows no pressure drops.

[Hondata]

Nope, if the injector duration is falling then it is the fuel tables.

[K24Miata]

Interesting, thanks. Time to go back to the tuner I guess.....

Another interesting data point (but perhaps not relevant), the car seems fine when we run in a straight line. We are only experiencing this issue at the exit of a hard corner.