Twin Cam EFI vs. Carb Ignition Coil Harley EFI & Harley Carb Discuss Twin Cam EFI vs. Carb Ignition Coil in the Harley Tech & Harley How-to forums; Can someone please explain what the actual difference is between the ignition coil for EFI models vs. Carbureted Twin Cams?...

[budzilla]

Can someone please explain what the actual difference is between the ignition coil for EFI models vs. Carbureted Twin Cams?

[cntrhub]

The technology has evolved into what is known as, "sequential fire." Old carb points and electronic ignitions would fire twice. Think of a set of points on a 4-cylinder. There are two points for 4 cylinders. But the points open twice. Once for fire on the one cylinder, but in the next sequence of that other cylinder about to see the spark, it is off a stroke and fires a blank cylinder that does nothing on the spark occurrence.

With the latest ignition, the dual fire or points firing twice is now eliminated. With the FI at this stage, has the ability to reference fire each cylinder on it's own. Meaning, it fires as if it was one cylinder with it's own fuel plot.

So, not only does the technology know what cylinder it last fired from, it now can tell you which cylinder lost spark. This is done with each individual coil. Known in some circles as a, "Spark Stick," you do not have to feel for a dead cylinder. The dash will tell you that the sequence needs to know who to fire off if that one spark stick is out of range as in a dead short inside; a short to ground; or the connector came off. These basic shorts will be monitored so as to guide you to who signed off on the, 'sequence' = Spits a code ~ Front bank code flashing bla-bal code number 1 or front cylinder. Something like that.

Basically, those are the two differences between coils. One coil without sequence uses one for all cylinders. And in sequence fire, you need one coil for each cylinder. The coding is self diagnostics. The individual coil is more for, 'starting purposes.'

[budzilla]

I'm not sure I'm following you. I understand the difference between dual-fire and single-fire ignitions. All 02-later Delphi EFI and carbureted models have one single-fire coil and fires each cylinder individually. My question is, why do the carb models use a different coil than the EFI models? Resistance?

[Hammerhead Pat]

I honestly don't know the difference between the two, but I do like your forum name! Sounds like an old Cheech and Chong movie Welcome to the forum, someone here will get you the correct info!

[shovelmike]

I wasn't aware whether there was a difference between the coil for an EFI bike and a carb bike. If they carry different part numbers my guess it that there is a difference in the resistance in the primary windings, these new systems are pretty touchy.

[frisco-rigid]

Hey Bud

You may be right,, resistance would be all it is unless they just want to make a guy think he'd better spend the dough to get the "correct" OEM coil..

All coils do the same thing with resistance being the diff..

They go from 5 Ohm's down to 1.5 Ohm's..

It is my understanding that you can use a Higher Ohm coil in a lower Ohm application but using a Lower Ohm coil than is recommended, could be destructive to the electrics.. I learned why once but forgot,, look it up and get back to us..

In-other-words, just for example, you can use a 5 Ohm "points" coil in an electronic ign that requires 3 Ohm's with no real prob..
But you should not use a 3 Ohm coil with points cuz it'll burn out the points contacts and make them arc.. I found out the hard way..
I have used a 3 Ohm coil with a DynaS that requires NO LESS that 5 Ohm's for a short time with no prob but I wouldn't advise it cuz I was just experimenting..