Ignition Coil question

[desmodoktor]

'02 M750, 7500miles.

What are the signs when an ignition coil goes bad?
Wet spark plug? compression loss? back firing? not steady rpms?

[Howie]

The cylinder with the bad coil will misfire.  Could this cause a wet plug?  Yes.  Compression loss?  NO, that would be mechanical.  Not steady RPMs?  Possibly.  So could a bad spark plug, coil, fuel injector, computer, vacuum leak, and several other possibilities.  Guessing is expensive.  Diagnosis is your friend.  The coils have a primary and secondary resistance (I don't know the spec for your bike)  A no spec shade tree diagnostic method is swap coils and see if the miss switches to the other cylinder.

[bikepilot]

^  There are basically two ways coils go bad.  First they can have an internal fault.  This is detectable by measuring the resistance of the primary and secondary.  Specs should be in the service manuals.  Most bikes run 2.5-4.5oh on the primary.

The second way they go bad is the insulation breaks down so that the spark rather than going out the wire and jumping the gap in the plug finds it easier to jump out the side of the coil and into something near-by.  If its this method of failure the oh reading won't pick it up, but the symptoms will generally be much worse when riding in the rain vs in the dry.

[ducatiz]

^  There are basically two ways coils go bad.  First they can have an internal fault.  This is detectable by measuring the resistance of the primary and secondary.  Specs should be in the service manuals.  Most bikes run 2.5-4.5oh on the primary.

Ducatis run 5ohm primary +/- 0.5

[bikepilot]

Good to know - that's a lot of resistance.  I wonder if any performance improvement would be had with a lower-resistance coil?  For comparison Nology coils tend to be around 2.7oh, stock SV coils are around 3.5-3.7oh and stock TL coils are around 4.2oh.

[Speeddog]

Good to know - that's a lot of resistance.  I wonder if any performance improvement would be had with a lower-resistance coil?  For comparison Nology coils tend to be around 2.7oh, stock SV coils are around 3.5-3.7oh and stock TL coils are around 4.2oh.

More here on primary resistance:
http://www.ducatimonsterforum.org/index.php?topic=45643.msg835880#msg835880

[desmodoktor]

here's what happens...
if i hold the throttle open on 2000rpms steady in Neutral.. the rmps are going to go up and down , 1700-2500rpms.. at the same time you could hear smth clicking in front of the bike.. looks like its under the air filter.. like its giving spark then shuts down , rpms go lower then it clicks again .. rpms go up.. and so on..
The spark plugs have 200miles on them .. when i pulled them out.. the vertical cylinder is white and dry.. however the horizontal is much darker and wet... if you see inside my 2 pipes .. one of them is darker than the other one.. which means one of them doesnt burn the fuel properly.. correct??
+ yesterday i was riding on the parkway.. doing 80mph @ 5000rpms .. for 30 min .. then i slowed down to 60mph @ 4000rpms.. and the bike started jumping up and down .. it would lose power than gain again .. backfire like 5-6 times and lose power again.. what i did is : dropped 2 gears and accelerated .. everything was normal after that..    idk what to look first ?
Does what i said make sense?

[ducatiz]

Good to know - that's a lot of resistance.  I wonder if any performance improvement would be had with a lower-resistance coil?  For comparison Nology coils tend to be around 2.7oh, stock SV coils are around 3.5-3.7oh and stock TL coils are around 4.2oh.

Some folks have experimented with the 3ohm type (from Dyna) and found they tax the charging system a bit more.

[junior varsity]

I've got the 3 ohm Dyna's on my M900 with no troubles. Will one day upgrade the rectifier to a mosfet one from Rick's Motorsport Electrics or rob an OEM from the new line of Ducati's, which have mosfet circuitry as well; and take Rick up on a higher-output stator.   That's neither here nor there, but the goal would be to provide stimulus to the heavily taxed charging system.  (Ohhhh, humorous language use when read thinking of contemporary political situations! har har har!)

[Graymonster]

I've got the 3 ohm Dyna's on my M900 with no troubles. Will one day upgrade the rectifier to a mosfet one from Rick's Motorsport Electrics or rob an OEM from the new line of Ducati's, which have mosfet circuitry as well; and take Rick up on a higher-output stator.   That's neither here nor there, but the goal would be to provide stimulus to the heavily taxed charging system.  (Ohhhh, humorous language use when read thinking of contemporary political situations! har har har!)

Hi. Im buying 3ohm Dyna Mini's to my m900 -98. Witch sperkplugs are you using  junior?

[LowercaseJake]

Liam from FastBikeGear recommends Nology PFC-06 (.6 ohm) for our bikes, fwiw. At least the carby ones. I used em briefly and they worked well, price is GREAT, you just have to be handy enough to fashion a bracket. Or go the zip tie route...