Barry Schwartz wrote:
>
> This is not meant as a flame (no pun intended), only a little
> clarification, without getting too technical -
> I . . .disagree with the following comment -
> [the car is supposed to backfire on the "overrun". "]
> When the one on my Truck failed (1.8 liter inline four), I got a nasty,
> VERY loud backfire whenever I let off the gas, especially during shifts
> when I was accelerating hard, which was most of the time with that small a
> motor :-). When I replaced the non operating "diverter valve", the
> backfiring stopped. That's WHY it's there. On my truck it's actually
> called an anti backfire valve, but performs the same function as the
> diverter valve. (vacuum controlled air diversion or re-routing so to speak)
> it's there to PREVENT backfiring, *NOT* to prevent a controlled burning in
> the exhaust, which is what the air injection is supposed to accomplish.
> Early air injected, emission controlled vehicles are purposely designed to
> run a richer fuel/air mixture, so there is additional unburnt fuel in the
> exhaust (just outside the combustion chamber, in the exhaust header or
> manifold) to actually promote this burning, when the air is injected, and
> just one of the reasons that early pollution controlled vehicles got a bad
> rap for poor fuel economy. Backfire, SEVERE backfire, not the nice
> popping/burbling sound from a cam at deceleration, is an indication that
> something is not operation correctly. Were talking about a violent
> explosion, at the tail end of the car, not a controlled burn. No auto
> manufacturer would actually cause it to happen, besides the damage it could
> cause, the noise would be unacceptable in any production vehicle, (we *are*
> talking about production, not racing vehicles) and would not be considered
> "normal operation". If it's backfiring LOUDLY, at ANY time, something is
> wrong. The purpose of all those controls, is to promote controlled
> burning, and reduce pollution of some form or another. A loud backfire is
> an uncontrolled burn, something definitely not the norm-
>
> Barry Schwartz (San Diego) bschwart@pacbell.net
>
> 72 FI, V6 Spitfire (daily driver)
> 70 GT6+ (when I don't drive the Spit)
> 70 Spitfire (long term project)
actually, we are both probably correct. since i ahve not heard your
backfire, i cannot comment on loud vs violent vs a satisfying burble
_there ain't no such thing as slightly pregnant - the diverter valve
does serve the function of venting excess pressure to atmosphere. the
air pump serves the purpose of inducing air into the system to eliminate
unburned fuel. overun is the one scenario where it is possible for a
volume of unburned fuel to be sent out the tailpipe. ted
--
Ted Schumacher
TS Imported Automotive
404 Basinger Rd.
Pandora, Ohio, USA 45877
Ph. 800/543-6648 USA/Canada FAX 419/384-3272 24 hour
Ph. 419/384-3022 - tech./general information
Web page http://www.tsimportedautomotive.com
New-Used-Rebuilt-NOS-Performance British car parts.
200 - 300 parts cars in our British-only salvage yard.
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