how to test ignition coil

[Josse]

Can anyone please explain how to test a  400/4 ignition coil using a multi meter

thanks Josse

[Johnwebley]

do you know the values/readings you want ?

 basically use the both power leads,and see if you have a circuit,

and the same ,with the plug leads remove the plug caps and check if you have a circuit,

its worthwhile renewing old plug caps as they tend to "burn out" with a greatly increased resistance  ,

[Lobo]

Hi Josse,

Within each coil there are two separate windings... the primary winding (a few hundred turns) & the secondary (HT) winding @ a few thousand turns. For the coil to work each winding must be complete. So... as John says, set your multimeter to the continuity scale & for test (1) put the 2 probes across the primary winding (yellow & black/white or blue & black/white),  and for test (2) across the secondary winding (ie the two spark plug caps)

In both cases there should be a complete circuit.

The manuals (I have) do not quote typical resistance readings.... and I can only suggest you test both coils and check that the results are similar (rather like compression testing). If they are ... well good.

Sadly the coils / leads / caps all 'degrade' due age, ie even if the results match you're not home & dry. Perhaps a kind member with new / known good coils could supply some readings.... I'm away from my bike til Feb unfortunately so can't help in the short term here.

Finally, why not lop the tip off a spark plug and in its place wind a stiff copper coil abouts the threads & then to a new tip... and crank the bike. If you can get a spark at (say 5mm) I'd reckon all's well.... the test equipment mentions 7mm. (But honestly I'm a bit out of my depth on whether this test would work / be valid ... Bryan...OddJob?)

Simon

[Bryanj]

If you remove the side electrode from an old plug and put this in a cap you should be able to get at least a 5mm gap jumped. The book does say 7mm and the testing machine used to overdrive the coils a lot I.E. make them spark a lot faster than at tick over so was a lot better than a kick over test.

I have had Lucas coils fail when they got hot but never a Honda one, if fact I have only changed them due to lead damage/too short or physical damage in an accident

[El__burro]

Set your multimeter to the continuity scale & for test (1) put the 2 probes across the primary winding (yellow & black/white or blue & black/white),  and for test (2) across the secondary winding (ie the two spark plug caps)

In both cases there should be a complete circuit.

The manuals (I have) do not quote typical resistance readings.... and I can only suggest you test both coils and check that the results are similar (rather like compression testing). If they are ... well good.
Simon

Sorry to jump on this thread but it is exactly what i was looking for.
I have done the test Simon suggests above and it gives me continuity when i connect either the blu and black/white or the yellow and the bl/w.
My issue is when i connect the ht leads from the same coil, they both read about 14.0 ohms but no continuity.
Faulty?

Thanks
El__burro
Cb750 k2

[Lobo]

Hi El_burro,

... "jumping on threads" is both welcomed, and more often than not, beneficial to all as new questions arise. And frankly, I'd quite like someone to jump in too... as HT circuits are not my strong point.

However.. my thoughts until put right...

At 14 ohms this secondary (HT) winding is certainly duff.... it sounds like some kind of internal short. Are you quite sure you've got the correct scale on your multimeter.... if you'd said 14K ohms we might have been in the right ball park; for whilst I can't find a specific value for these old Hondas, most searches I do, state HT coil norm ranges between 10 Kohm - 20 Kohms.... ie about 1000x the value you're getting.

So yup, your HT coil is indeed showing continuity (ie not open circuit)..... but in this case, too much!

Simon.

(the primary winding / low voltage circuit should be abouts 5 ohms I think)

[AshimotoK0]

I am just getting all of the materials together to do a write-up on refurbing coils (materials must be cheap and readily available to everyone) . Main thing is replacing the HT leads (as I briefly mentioned in an earlier post). So watch this space ! On the primary, if you don't have a meter that measures low ohms accurately then connect the two primaries in series on the pair of coils and connect (briefly) across a 12v battery. Measure the voltage between the centre point of the coil connections and + terminal and then negative terminal. If the coils are OK then the coils will act as a 'potential divider' and you should have roughly half of the battery terminal voltage at the mid point (within 10%). Obviously, if you have a meter that measures low resistance accurately , which from memory is typically about 4.5 Ohms, you can simply measure it. (this assumes that both coils don't have a faulty primary (RARE!))

I think shorted primaries are a rare occurrence on 'Tec' /  Nippon Denso coils though (well on all of the ones I have seen) , it always seems to be the  the HT lead  that fractures , hence my restoration write-up I am doing. On the US import CB350K1 I got from DK last year, all the electrics were all in  pretty much pristine condition for a 45 year old bike but the HT leads look floppy around the exit point from the coil and, even though the resistance meters out  OK, I will replace them.

Ash

[SteveD CB500K0]

Ash - a few years back I added a FAQ on the US site which showed how one member had replaced the HT leads on original coils (lots of epoxy if I remember)

Have you seen this?

Maybe we need a FAQ on here as I see more and more really useful stuff that won't get indexed properly (eg Bodd's 400/4 wiring diagram won't show up in a search as it doesn't use the words "400", "wiring" and "diagram" anywhere in the text!

[AshimotoK0]

Ash - a few years back I added a FAQ on the US site which showed how one member had replaced the HT leads on original coils (lots of epoxy if I remember)

Have you seen this?

Maybe we need a FAQ on here as I see more and more really useful stuff that won't get indexed properly (eg Bodd's 400/4 wiring diagram won't show up in a search as it doesn't use the words "400", "wiring" and "diagram" anywhere in the text!

Yes I am using epoxy (liquid) and black epoxy putty Steve. Problem is I have access to stuff other members (test gear/chemicals)  may not have so I want to stick to readily available materials. One hard to get item is the thin walled rubber sleeving that goes over the HT lead. I'ts around 1mm wall thickness which is really  hard to find in nitrile rubber.

Ash.