Why does spark exceed spark table value (sometimes) on decel?

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canuck1
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Why does spark exceed spark table value (sometimes) on decel?

Unread post by canuck1 »

The highest value anywhere in my FN2200 spark table is 43, but for some reason, after moderate accel to 4000 rpm, followed by a closed throttle decel I have logged as high as 49 dbTDC, generally about 2 secs after releasing the go pedal.

Just wondering why this happens?

Sean
canuck1
Posts: 67
Joined: 2021 Mar 31, 17:29
Location: Victoria, BC CANADA
Vehicle Information: QH, TunerPro RT 5, GUFX_220418.xdf, A9L2_220405, DECIPHA_220505.ADX, 395w, AFR 195CC Renegade heads, Comp XE274HR cam, Siemens-Deka V 80lb/hr (shorties), Mass-Flo-EFI style 4bbl throttle body with GM maf on top. Custom long tube headers, sidepipes, 5 spd manual.

Re: Why does spark exceed spark table value (sometimes) on decel?

Unread post by canuck1 »

OK, looks like FN389 Dashpot CT spark multiplier is the culprit! the actual dbTDC value made me nervous but checking it against FN389 x SAFTOT, I can see it's adding timing to try and more quickly stabilize idle speed from closed throttle transition.

Sean
decipha
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Re: Why does spark exceed spark table value (sometimes) on decel?

Unread post by decipha »

yep
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