Unusual Problem (I Think)

[Yellow05C6]

So this is an unusual combination. But I see this issue in my

[Yellow05C6]

So this is an unusual combination. But I see this issue in my ’06 Z06 also. Low speed ‘chatter’. At 25-35 MPH in 1:1 drive the engine seems to surge then relax with the result being a lot of drivetrain chatter. Now for the combination: It is a ’72 Vette ‘restomod’. It is a GMPP ZZ6 350 ci engine with port injection / single plane intake / Holley throttle body and a 411 ECM (OS 12212431). The distributor is a ‘dual sync’ modified so that it creates both the cam and crank signals for a Chevy Express Van (Low Resolution Crank signal). The transmission is a Tremec 5 speed w/ a 3.73 rear end. The car runs great in all other conditions. But this combination even chatters in 3rd gear! I can minimize the problem by lightly cycling the throttle, adding load then reducing it. Any insight into how to eliminate or even just reduce this problem would be appreciated. Maybe disable Spark Smoothing?

[dhoagland]

Can you post a log, possibly your tune file too...
My knee jerk reaction is o2 sensor feedback (trailer hitching), but if you're open loop that aint it

[Supercharged111]

Could also be timing related, I believe in that area of the map you want to kind of flatline the timing to reduce cam surge.