DeTomaso Mailing List: March 2000, Message #55

On Thu, 2 Mar 2000, Steve Liebenow wrote:
> As a hardware engineer.... I have a real problem with a software type
> trying to esplain hardware functions.....  :)))

Always the potential for massive confusion there... but I did do well in
fizzix in college, so I guess I can play both sides of this fence.  :-)


> Andy's description of the wasted spark theory has my brain buzzing
> backwards.... not getting into the theory of electron flow and
> what-have-you.... but, how can a plug fire backwards when the ground
> potential is the same as another plug....

In a wasted spark ignition system, the block is not grounded relative to the
spark - it floats with no particular potential.  The coil high-voltage
windings are not grounded on either end.

The current travels from the coil through one spark lead to the center
electrode of one spark plug, jumps the gap from the center electrode to the
side electrode (which is the backward spark), travels through the block to
the side electrode of the other plug, jumps the gap from the side electrode
to the center electrode (the forward spark), and returns to the coil through
the other spark lead... completing the circuit.

By the way, the spark in the cylinder which is not on the compression stroke
(it is instead on the exhaust stroke) is an "easy" spark because the
ionization potential in that cylinder is low due to the low pressure.  And
yes, motorcycle engines have used wasted spark ignition for eons.

-Andy
#3822

72 Pantera - Rocky             91 Miata - Steve                 96 A4Q - Rudolf
80 928 - Phantom        87 E350XL - Andylance (FOR SALE)       84 RZ350 - Sting