What causes a throttle to close and reopen during a dyno run?

[davepl]

I was watching a dyno run of a modified LS7 (on an engine dyno, not chassis) and the throttle was closing itself about half way and reopening around 4500rpm. I couldn't hang out to find the cause, but I always was curious what would cause the ECM to do it...

I do know they were having trouble keeping up sufficient fuel pressure on the high end, where it was taking a great deal of volume and still wanting 60psi (at close to 700hp mind you). But I didn't think that was related.

Someone is now describing that issue on an LT-4, and I'm curious as to the cause. Some have suggested the DD tables, but I'm too new to proffer a guess.

Can anyone explain what strategy or event would cause the throttle to back off during a dyno pull like that? I have no idea if it will throttle cut when it goes lean, for example, so it's a total noob question but I appreciate you humoring me (presuming you do!).

I'm guessing its when actual torque production exceeds the amount commanded by the driver demand table, but I could use an overview of that even if that's right!

Thanks!
Davce

[Higgs Boson]

The ECM can and will reduce output when things don't look right. Could it be fueling? Yes. Could it be as simple as achieving commanded torque? Yes.

Typically you will want to post the tune if you want more specific answers.