Over run backfire

[inj gtr202]

Kind of a bit of wank factor... but...

My old tune used to have a nice crackle and backfire after I gave it a good boot full then backed off the throttle and held it in gear.
Would it be because I'm using closed throttle maps to control the idle and spark at closed throttle that I'm not getting these events anymore? (pretty sure my old tune did not have closed throttle control)
Also what causes it ? high fuel loads? more spark advance ? (in the high vac areas obviously)
cheers

[antus]

Its the decelleration fuel cut functioning in $12p that stops it. Ive actually noticed the same thing in my car and considered disabling the fuel cut to get it back, it certainly sounds nice

Having said that, I havnt tried it. I would try raising "Decel Enleanment Param - Min DE BPW" a couple of milliseconds at a time so it cant cut your fuel completely and has to leave a bit in the pipes. The other Decel enleanment parms could probably be tweaked instead if that doesnt create an even crackle through the decel period

[inj gtr202]

Its the decelleration fuel cut functioning in $12p that stops it. Ive actually noticed the same thing in my car and considered disabling the fuel cut to get it back, it certainly sounds nice

Having said that, I havnt tried it. I would try raising "Decel Enleanment Param - Min DE BPW" a couple of milliseconds at a time so it cant cut your fuel completely and has to leave a bit in the pipes. The other Decel enleanment parms could probably be tweaked instead if that doesnt create an even crackle through the decel period

I have managed to get a direct copy of my old $A5 tune to run in $12P (thanks Holden 202 ) and even in $12p it has a nice over run backfire. I am however not running any closed throttle control so it runs exactly as it did before ( rich crap idle and rich light cruising). I am now going to turn on the closed throttle control and take some fuel out the high vacuum areas on this tune because it is dyno proven tune and does actually feel faster than my attempt at copying it.

Will see is it still crackles nicely by the time I finish leaning it out.

[Holden202T]

from memory the AFR table in that tune is a bit all over the shop, i didn't really want to copy it because of that, but after all the issues you had i just did straight copy over to prove that your tune would work in 12P with the A5 numbers and go similar.

i guess its something you can work on later but something to keep in mind