This is the 3rd engine I've tuned with a Powervision. (Two 110s and a 120R) All make great power and run cool and smooth. However, each one all had a decel pop or two right around 1800 rpm.

I know it's not just me, I hear this in so many Twinkies of all displacements.

What are the recommendations for smoothing this out or eliminating?

FYI, it's basically as stock CVO Limited 110 w/ Jackpot XXX 2-1-2 header, V&H Monster Ovals and ventilator ac.

 

I get absolutely no decel pop, I run 13.8 afr in the 20kpa range.

 

I too am running 13.8 in the 20kpa range.

 

You could add some spark advance in the decel columns front and rear if both are popping and lower the decel enleanment table by 10% at a time till it's gone or you get to 0 in the temp ranges you have pop. And go even richer in the AFR 20 Kpa column.I'm at 13.6 MOL. Try to find a balance between all 3 areas.

 

Thanks, I'll try that.

 

The ECM pulls timing at 1800 is what I read on rapid rpm drop

 

I hadn't heard that,But you may be right. I''ve also enabled Closed Throttle Spark after seeing some zero's in spark advance columns in data logs, however there were 0's at higher RPM's yet still during deceleration,But not all the time. So in the 118 *F Columns of the CTS ,I've set the tables to match my Spark Advance tables.Been so long I'd forgotten about that. Oh, I enabled those tables by setting Closed Throttle Spark Max TPS to 0.9.

 

after reading that I went to my data logs and sure enough it can be seen. yes there are times of zero advance at other times but brief ones and not noticed like the one at 1800. I think a lot of PPL try to tune out an event caused by the ECM without knowing

 

Add fuel in the affected range. I like using a 12.5 - 13.00 AFR between 1200-2500 RPM.


During decelerating (throttle plate closed) there is a lot of vacuum. This cause the air fuel mixture burn slower due to the low pressure. Any unburned fuel enters the hot exhaust manifold and causes the popping. Adding fuel actually increases cylinder pressure under these conditions and burns the mixture faster.