Jim Miller WB5OXQ wrote:
>The timing is controlled by a crank position sensor at the flywheel and the
>device in the distributor controls the injector timing so if it is off that
>is causing fuel to be injected way off time and that would definately cause
>backfiring
>
>
Its very hard to make a late-model EFI system backfire. This is
especially so with the Magnum beer-barrel intake manifold with its long
runners. This usually means something is bad wrong. In order to get
combustion into the intake manifold it would take some kind of fuel
entering at a point earlier than the fuel injectors and then getting
ignited somehow. Valve timing is the usual suspect. I would seriously
doubt that the distributor fuel-sync would cause this. In fact, you can
loosen up the dist holddown and turn the dist in either direction as
much as you want and most people cannot tell any difference in the way
the motor runs. There is a "sweet-spot" dont get me wrong - but this is
usually less than 10 degrees (out of 720 degrees) of crankshaft
revolution and only results in small fluctuations in rpm (typically
3-400 and in rare cases 600rpm) mostly at idle - that and about < 1mpg
fuel economy difference. Think of it this way - if the injector(s) were
CONTINUOUSLY supplying fuel in all 720 degrees of crankshaft revolution
(actually very common as injectors leak) - all of this fuel will be
sucked away at the next intake valve event. When that intake valve
opens - if there is ANY hot gasses or combustion still in the chamber -
you WILL get backfire. Thats fuel sync vs timing re: backfires.
Shane
This archive was generated by hypermail 2b29 : Fri Feb 06 2004 - 11:46:36 EST