This is an image of the dyno plot of my new motor, compared to the old one before a side seal let go. We are unable to determine the cause of the rough power curve and would appreciate any info if you have seen something similar. Trying to get it on track this weekend.

It is in my race car and the only relevant mod it has is a 55 mm intake restrictor and a RB computer flash.

We've tried new coils with no change, double checked intake valve wiring/plumbing. Intake is stock. Injectors were just serviced.

Thanks,
AC

 

That break-up at the high end looks a lot like bad coils, but you say you've tested that.
Was the same restrictor and RB flash used on the previous engine?

Is it pulling timing at all?

 

Looks the same with previous coils (Sake Bomb), above is stock coils.

Yes, restrictor and ECU unchanged.

Haven't logged timing during a run, not sure how to do that actually.

Forgot to add that knock sensor is connected but isolated from the engine.

 

Hrmmm. Might want to connect that knock sensor back, if possible. I guess if it was really knocking you would have found out the hard way by now. But it still wouldn't hurt.

AFR doesn't seem to do anything weird, right? Hard to see in the photo.

 

And the diagnosis was:

Bad APV servo motor. Interesting that it did not throw any codes.

Thanks for reading

AC

 

Cool, nice find. I'm kinda curious how you diagnosed that given that it threw no codes. Just for my own education

 

Swapped in a known good one and problem was resolved.