Tech'ish question. Inquiring minds want to know.

[rapieper at yahoo.com (Ron Pieper)]

I can only answer by telling you my experiences with this via Megasquirt, where I learned from
someone on their forums that you can eliminate the backfiring you are desiring by leaning out the
mixture at VERY low vacuum levels - seen only with the situation of zero or negative load with the
engine typically decelerating.  With MS, that's really easy to do.  I leaned out that range, and
presto, no more pop-pop-pop.

This was only evident with my free-flowing exhaust (straight through) because a normal exhaust
muffles it greatly.

Sooo...we can extract from that that your engine is getting more fuel in those conditions than it
needs, and some 'explosion' is likely happening in the exhaust system.  With CIS, I reckon you're
stuck with it.

I guess the little holes you write of could cause or amplify this, but it happens anyway under the
right conditions.

Dan Bubb, please shed your light here.

HTH

Ron

--- Scourge <scourge@cogeco.ca> wrote:

> So I've been wondering. 
> 
> What makes a car backfire? Not regular loud single shot backfires, but the awsome little pop pop
> pop some cars have on heavy downshifting.
>  My golf used to do it like mad, I loved it. Made it sound so raw and hardcore, lol. Non of my
> rocco's have ever done it.
> 
> One guy I know once told me it was cause by small holes farther up the exhaust(I guess he meant
> near the DP) that while leaking a bit would also create a sort of scavenging effect and pull
> some air back into the exhaust system. That air had oxygen in it and could then act as an
> accelerant with the bit of unburnt fuel and it would ignite in the exhaust, thus creating the
> "pop pop pop" when downshifting. I have no idea how accurate this is.
> 
> Any thoughts/input??
> 
> -George -missing crazy things my golf could do(like shoot flames out the tailpipe!)
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