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How to test CDI, Magneto stator coils & Ignition coils on Fuji engines
The following applies to Polaris blue Fuji engines (except the Pro 785).
Polaris red domestic engines are covered in a different thread.
According to the 1992-1998 Service Manual, the Fuji 780 stator and ignition coil ohms are as follows (1997 780 Fuji engine used for reference).
Notes: 1992-1993? Fuji 650 engines may have slightly different test numbers (750 also?)
The 'early' Fuji engines used an 'analog' version of the ignition system, later year Fuji engines use the 'digital' system. The exact differences are unclear to me at this time, but CDI and stator from the two types can not be interchanged.
In most cases, the wires are to be unplugged from everything else when testing a component.
The actual CDI can not be tested. What you do is test everything around and connected to the CDI (including stator and all grounds). If everything else seems correct, then the CDI may need replacing.
In many cases, a replacement CDI from a different year or engine size can be used. You may need to compare the ignition timing curves to confirm that you will not have overly advanced or retarded ignition.
Some Fuji owners have even converted to the more aggressive Pro 785 CDI, but this requires changing the ignition coils and related wiring.
Red/Purple to Yellow: 0.6 ohms (Alternator coil - battery charging)
Red/Purple or Yellow to Black: Infinite/open/no connection
White/Yellow to Black: 220 ohms (Trigger coil)
Blue/Red to Red/White: 90 ohms (Pulser coil)
Red/White to Black: Infinite/open/no connection
Red/White to Green/Red: 490 ohms (Exciter coil)
Black stator wire grounding check
Disconnect the wires from the battery negative, then check Black stator wire ohms to the end of the heavy Black battery wire, and separately to the end of the smaller Black battery wire (if you have one). Both measurements should be under 1.0 ohms, and very close to zero ohms.
I think there should be zero ohms between the Black ignition coil connection on the CDI to the engine block (with battery negative wires disconnected).
All ground connections must be clean and tight. Grounding is critical to proper operation.
Side note: As far as I can tell, two of the three ignition coil secondaries are grounded through the other coil primaries to reach the actual black CDI wire and engine ground.
A rather unusual configuration
Ignition coils (each)
Black to Black/White: 0.6 ohms
Black to Secondary lead: 3.3K ohms (3,300 ohms)
Black to Black/White (with all three coils connected in series), but not connected to CDI: 1.8 ohms
The spark plug caps/boots should measure 5,000 ohms (5.0K ohms) each.
Total resistance through spark plug cap and wire and coil should be about 8K ohms to 9K ohms
Note: Ignition coil primary wires are connected in series.
If any of the coil primaries is open or shorted, none of the coils may be able to fire the spark plugs.
All three spark plugs fire together, every time. Three sparks per crank revolution. It does not matter which spark plug/coil connects to which cylinder.
Exception is the Pro 785 CDI, which fires each spark plug separately.
Other possible causes of no-spark
Black/Yellow stop switch may be shorted to ground.
With Black/Yellow wire to CDI unplugged, do you have spark?
If yes, then check Black/Yellow wiring and stop switch.
With lanyard in place, Black/Yellow switch wire to ground should measured open circuit. Lanyard removed, should measure near zero ohms.
Polaris red domestic engines are covered in a different thread.
According to the 1992-1998 Service Manual, the Fuji 780 stator and ignition coil ohms are as follows (1997 780 Fuji engine used for reference).
Notes: 1992-1993? Fuji 650 engines may have slightly different test numbers (750 also?)
The 'early' Fuji engines used an 'analog' version of the ignition system, later year Fuji engines use the 'digital' system. The exact differences are unclear to me at this time, but CDI and stator from the two types can not be interchanged.
In most cases, the wires are to be unplugged from everything else when testing a component.
The actual CDI can not be tested. What you do is test everything around and connected to the CDI (including stator and all grounds). If everything else seems correct, then the CDI may need replacing.
In many cases, a replacement CDI from a different year or engine size can be used. You may need to compare the ignition timing curves to confirm that you will not have overly advanced or retarded ignition.
Some Fuji owners have even converted to the more aggressive Pro 785 CDI, but this requires changing the ignition coils and related wiring.
Note: For testing low ohms, you must first check your meter offset.
Short the probes together, and record the ohm reading. Do this again to confirm the reading.
This is your meter's ohm offset - the amount that the reading differs from the actual ohms.
When you measure a low ohm coil/wire, record the number.
Now subtract the offset from the measurement - the result is the actual ohms value of the thing being measured.
Example: Probes shorted, meter reads 0.4 ohms.
Probes connected to coil being tested, meter reads 1.1 ohms
Subtract the 0.4 offset from 1.1 reading gives you 0.7 ohms actual
1.1 - 0.4 = 0.7 ohms
Most digital multi-meters are only accurate to within 1 or 2 counts, so a meter reading of 1.1 could actually mean 1.0 or 1.2
Magneto stator coilsShort the probes together, and record the ohm reading. Do this again to confirm the reading.
This is your meter's ohm offset - the amount that the reading differs from the actual ohms.
When you measure a low ohm coil/wire, record the number.
Now subtract the offset from the measurement - the result is the actual ohms value of the thing being measured.
Example: Probes shorted, meter reads 0.4 ohms.
Probes connected to coil being tested, meter reads 1.1 ohms
Subtract the 0.4 offset from 1.1 reading gives you 0.7 ohms actual
1.1 - 0.4 = 0.7 ohms
Most digital multi-meters are only accurate to within 1 or 2 counts, so a meter reading of 1.1 could actually mean 1.0 or 1.2
Red/Purple to Yellow: 0.6 ohms (Alternator coil - battery charging)
Red/Purple or Yellow to Black: Infinite/open/no connection
White/Yellow to Black: 220 ohms (Trigger coil)
Blue/Red to Red/White: 90 ohms (Pulser coil)
Red/White to Black: Infinite/open/no connection
Red/White to Green/Red: 490 ohms (Exciter coil)
Black stator wire grounding check
Disconnect the wires from the battery negative, then check Black stator wire ohms to the end of the heavy Black battery wire, and separately to the end of the smaller Black battery wire (if you have one). Both measurements should be under 1.0 ohms, and very close to zero ohms.
I think there should be zero ohms between the Black ignition coil connection on the CDI to the engine block (with battery negative wires disconnected).
All ground connections must be clean and tight. Grounding is critical to proper operation.
Side note: As far as I can tell, two of the three ignition coil secondaries are grounded through the other coil primaries to reach the actual black CDI wire and engine ground.
A rather unusual configuration
Ignition coils (each)
Black to Black/White: 0.6 ohms
Black to Secondary lead: 3.3K ohms (3,300 ohms)
Black to Black/White (with all three coils connected in series), but not connected to CDI: 1.8 ohms
The spark plug caps/boots should measure 5,000 ohms (5.0K ohms) each.
Total resistance through spark plug cap and wire and coil should be about 8K ohms to 9K ohms
Note: Ignition coil primary wires are connected in series.
If any of the coil primaries is open or shorted, none of the coils may be able to fire the spark plugs.
All three spark plugs fire together, every time. Three sparks per crank revolution. It does not matter which spark plug/coil connects to which cylinder.
Exception is the Pro 785 CDI, which fires each spark plug separately.
Other possible causes of no-spark
Black/Yellow stop switch may be shorted to ground.
With Black/Yellow wire to CDI unplugged, do you have spark?
If yes, then check Black/Yellow wiring and stop switch.
With lanyard in place, Black/Yellow switch wire to ground should measured open circuit. Lanyard removed, should measure near zero ohms.
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