Any Idea What's Causing This? - 98 Vette
 

Pretty much stock 98 Vette A4. Only a Corsa Catback and some kind of K&N dual cone filter kit. That's it. Everything else was stock. 104K miles. Was tuning it on the dyno and every pull had the little dip. Absolutely nothing showed up in any of the data logs that might be causing it. Any ideas?

http://www.MyOnlineImages.com/member.../98Vette_1.jpg

there was a post where someone figured out why (very long post) and a pretty well known person on here. But from what I followed in the post he hinted but never released the info. Best guess is in the tune or converter locking or unlocking. Hopefully someone else will chime in with some info. I tune mine myself and its not in mine but it is common on c5s.

I saw one like this before and it was a fuel pressure drop off causing the motor to lean out.

Looks kind of like timing being pulled out for some reason.

My car was getting false knock and looking like that, so we mellowed-out the knock sensors.