Hondata

Looking for advice on what else to try for smoothing out this symptom. At very low throttle inputs in cruise conditions, the engine goes in and out of overrun cutoff resulting in a surging/bucking of the car.

Contributing factors: high compression (12.5), big cams (Kelford 179-B), big injectors (FIC 900). The engine delivers quite a bit of engine braking. It's also running on E85, though that should not matter.

KPro V4 on a PRB ecu

I've dialed back the Overrun Cutoff MAP values and that helped. Interestingly, going from 10 KPa to 0 for Cutoff made a noticeable improvement even though the MAP signal never gets below 30. But it still cuts off/on even when set at 0.

Since the log does not have precision other than single full units of %, I can't tell if there is something changing in the TPS signal...maybe a half-percent? Pictured starting at 3:10 is a logged sequence where the TPS signal reads 0%, yet the Overrun Cutoff comes and goes. This is me tooling around in my moderately hilly neighborhood in 3rd gear @ 2800 rpm. There also another sequence around 4:10.

So it appears that TPS is the primary trigger for Overrun Cutoff, even though the MAP signal trigger point is the only one that can be changed in the tune. True?

Thoughts on additional ways to make this smoother?

You are hitting a rev limit. Try disabling the lean protection.

Spunkster wrote: Mon Apr 22, 2024 9:10 am You are hitting a rev limit. Try disabling the lean protection.

Tried it...no help.

Lean Protection shouldn't be in effect anyway, since I have that set for "Engine Load is over 89 kPa"...and this is happening at minimal MAP levels.

I also tried "Disable Fuel Overrun Cut-off Delay" ...no help there, either.