In a message dated 2/10/00 2:05:57 PM !!!First Boot!!!, DICEMAN469@aol.com
writes:
<< Ok, who can explain how the computer controls the timing?? The way I see
it,
the coil gets power and doesn't fire until the rotor passes on distributor
cap contact. I don't see any type of vacuum or electronic soleniod advance
on
it, so I am confused. I know I can push more timing on this engine without
pinging, and I'm trying to find a way to do it, without sending the computer
back to superchips.
>>
The computer has no idea where the distributor rotor is, it relies on the
distributor being properly installed for this.
Here's my explanation:
When the truck is cranked, the computer has no idea where the engine is in
the rotation, so no spark or fuel injection is provided. As the truck is
cranked, the computer looks at two sensors, crank position sensor and
distributor synch sensor.
While rotating, the signals look something like this for a V8 (crank on top,
synch on bottom):
________---_______---_______---_______---________---______---______---______--
-________---__
________---___________________________________________________________________
---__
The crank postion indicates each cylinder passing TDC (or some fixed value
below TDC) and the
synch signal indicates #1 cylinder passing TDC (or some fixed value below
TDC). The crank position sensor would be sufficient if
it were only used for the ingnition timing, because the computer fires the
coil based on this signal, and
the relies on the distributor rotor to mechanically route the spark to the
correct cylinder.
Because the magnum is sequentially fuel injected (meaing only the cylinder
that is on the intake stroke gets a fuel charge), the computer
needs a place to start the injector sequence (The sequence is constant and
follows firing order).
The distributor synch is onlyused during cranking to tell the computer which
crank
position pulse is the #1 cylinder, thus the beginning of the injector firing
sequence.
Once the sequence is started, then the crank position pulses are all that is
required to tell the
computer to fire the injectors.
Ignition timing can be advanced or retarded by controlling how long after the
crank position pulses occur
that the computer fires the coil.
Fuel injection timing, once initialized, is not changed, only the pulse
widths (injector ON time) is changed.
Newer Distributorless ignitions have one coil for every two cylinders, and
fire the individual coils similar to the
way sequential injection fires the injectors, but two cylinder get the spark,
one on the compression/power stoke
transition, and one on the exhaust/intake stroke transition.
Even newer coil on plug systems have an ingnition coil on top of each plug.
The computer sends a low voltage pulse to
each coil when required, and the coil fires the plug. No more high voltage
ignition wires, so higher voltages can be used without
risk of wire breakdown and electrical noise.
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