4
Part #FAST4-101
Revised 7/9/07
FAST™
3400 Democrat Rd.
Memphis, TN 38118
Phone: (901) 260-3278 Fax: (901) 375-3408
www.fuelairspark.com
Ignition Strategies
CRANK TRIGGER:
Using a crank trigger with an XIM™ is similar to using a crank trigger with an XFI
™
. The crank
trigger is used to determine engine speed and position. And a separate cam input signal (one pulse
every two engine revolutions) is used to locate the start of the firing order. As with an XFI™, the crank
trigger should be installed so that the pickup and one of the magnets in the crank trigger wheel are
lined up with each other when the engine is approximately 50 degrees BTDC.
The number of crank pulses the XIM™ expects to see per revolution (number of magnets in crank
trigger wheel) is equal to half the number of cylinders. An 8-cylinder engine uses a crank trigger wheel
with 4 magnets, a 6-cylinder engine uses 3, etc.
The cam signal needs to occur between 10 and 80 degrees before a crank input (which works out to be
between 60 and 130 degrees BTDC for a 50 degree crank reference angle). The cam input is typically
setup to occur before the crank pulse that corresponds to the first cylinder in the firing order. But other
locations are permissible with appropriate coil wiring.
The XIM™ has two sets of outputs for controlling coils – EST and COIL. The type of coil being used
determines which set of outputs is needed.
The EST outputs are used with “smart” coils such as those found on GM LS1 engines. These coils
have built in coil drivers. They are controlled by a 0-5V square wave. They charge while receiving a
5V signal and fire when the signal drops to 0V.
The COIL outputs are used to directly charge traditional (usually 2 pin) coils. Each coil is connected to
a COIL output from the XIM™ and to switched ignition power. The COIL outputs are held low to
charge the coil and released to fire the coil.
The coil outputs – either EST or COIL – fire one at a time in alphabetical order starting with output A.
They need to be wired to each coil according the engine’s firing order. EST/COIL output A goes to the
cylinder associated with the first crank signal after the cam input (which is typically the first cylinder
in the firing order.) The following table shows examples of coil wiring for a small block Chevy with a
1-8-4-3-6-5-7-2 firing order.
XIM™ EST/COIL Wiring (Coil per Cylinder) for Different Cam Signal Locations
EST/COIL Output
A
B
C
D
E
F
G
H
Sequence after Cam Input
1
ST
2
ND
3
RD
4
TH
5
TH
6
TH
7
TH
8
TH
Cylinder # (SBC w/ Cam Before #1 Crank Signal)
1
8
4
3
6
5
7
2
Cylinder # (SBC w/ Cam Before #4 Crank Signal)
4
3
6
5
7
2
1
8
