Intermittent timing dropping to nearly zero at steady state cruise, repeatedly.

[NotSure]

This has been annoying, it causes a single "bump" when it happens, like a quick tap on the brakes.

Stock Gen4 6.2L with 2.3L Whipple. I have attached the cal and a small section of log where it was doing it repeatedly. At steady cruise, timing drops to nearly 0 for an instant (200 ms) and then returns. Holding a steady throttle it will do it over and over. I think I have every spark retard modifier logged but see nothing. The MVPI3 data in the log is just a manual switch marker I have wired in to mark areas in a log. I never see this happen under accel, just light steady cruise. Anyone have an idea?

[ABADZL1]

Are you running the AC when this happens?

[jsllc]

Yep I have seen this. Log all the PIDs related to timing and you should see why.

[Gpargament]

I agree with above i need to see timing is being affected, is it base advance, cfco advance, knock retard, burst knock, iat advance, idle/coast advance, etc... does your car come stock without spark smoothing enabled? not sure if that will help or not, but i know my spark transitions are smoother with it on.

[NotSure]

Thanks for the replies, I completely spaced the idea of a/c operation. I do remember just after the whipple install I reduced the a/c torque reduction (ECM 12888) about 20% at the 45 kpa MAP column, as it seemed to really "hit" when it cycled on and off at idle, which seemed to fix. But if anything, it would need to be reduced further (less torque reduction) to prevent the chug. Don't want to just slam it on and off, but it probably doesn't matter with the mass of the blower being driven on the same belt.

I wasn't logging a/c operation, will have to do so and confirm that is what it is. I did log all of the available spark retard pids, but not all of the advance ones. Spark smoothing is disabled in the stock tune and I have left it that way.

[ABADZL1]

I zero the ac tq table. The one under the torque management tab I believe. There's also ac compressor ramp in/out airflow settings that I tweak. I dont see the spark drop anymore when it cycles on/off

[RobZL1]

Ditto to that. Zeroing that a/c torque table will eliminate the feeling of it kicking on and off while cruising in my experience, and the ramp in/ ramp out at idle can be tweaked to keep it from throwing the idle too far out of control when it cycles.

[aharonc]

I get the same thing after I accelerate to redline and then just cruse.

[NotSure]

Thanks to everyone for the replies, zeroing ac torque reduction was the fix. Finally got around to driving it to confirm. Seems so simple now. So far I haven’t needed to adjust the ramp in/out for idle, but it is a stock cam, stable idle.