- Hey I'm Evan, head of engineering for RM Stator.
Today we're gonna talk about testing ignition coils.
They're an important part of your
ignition system and they're easy to test.
They do have coils of wire inside them
so we can measure the resistance
across those coils and make sure that they're correct.
So make sure you look up the spec on
our website so you know what you're testing for,
and set your meter accordingly and
I'll show you how to test a couple of 'em,
and that'll be a good way to make
sure your ignition system is working correctly.
Okay, so we're gonna start with a
simple single spark plug ignition coil.
These coils have two coils inside of them,
a primary and a secondary so the
primary we can always test between,
there'll be some sort of wire coming out
or a terminal, at least one if not two.
There's only one terminal, we're gonna
measure the primary resistance,
the primary coil between the terminal or the wire and
ground or the mounting bar that runs through it.
So you can see there's a metal bar that
goes through the center of the coil.
If there was two terminals like
some other coils have or two wires,
we would measure the primary between the two wires.
So here I'm gonna hook up my meter
between the terminal and the grounding
or mounting bar in the center.
And the primary resistance is generally
very low on an ignition coil.
Some are around one ohm or less,
can be as high as three or so on a
performance coil, just depends on the model.
So, you always wanna look up the
spec on our website so you know what
you're testing and what is should be.
So here I can see that it's measuring
about point five for the primary, so that's fine.
And now I'm gonna measure the secondary.
So, depending on the type of coil
there's different ways to measure it.
On this coil that's meant for a
single spark plug, the secondary coil is
between the ground or the mounting bar in the center,
and the spark plug terminal at the end of the wire.
So to reach it, I'm gonna go ahead and
put this in here and plug it down in there.
So this should be in the thousands of ohms.
I believe this one's rated at four point five K,
or 45 hundred ohms, so I can tell
that my meter's not showing anything.
Well, it's 'cause it's set to expect a
measurement of two hundred ohms and
I'm trying to measure four point five K or 45 hundred.
So I need to bump it up to the 20 K setting,
which is closest resistance range
above what I'm trying to measure,
and now I'll see that the meter
jumps up and show four point five K which is correct.
So for a simple single spark plug ignition coil like this,
that's how you measure the primary and the secondary,
and that tells us that the coil's
in spec and should be working fine.
All right, here's a different kind of
ignition coil similar to the other one
but this one is meant to fire two spark plugs,
so we see it as two plug wires coming out.
If we look at the other side, we also see that
it has two wires for the wiring harness connection.
So basically, we test it the same way,
it just looks a little different.
So to test the primary coil inside,
we're gonna connect between the
two wires that connect to the wiring harness.
And again, the primary resistance should be low,
so I looked up the spec, I know it's about half an ohm
which is what I'm measuring and
I have my meter set to the lowest range to account for that.
So that looks good, then I wanna test the secondary.
Now the difference on a dual output coil like this is
you measure the secondary between the two spark plug wires.
You're not measuring from the mounting or
grounding bar to one or the other.
So to take my secondary measurement,
this doesn't have caps on it so
I've put some nails down inside
to connect to the wiring inside.
So I connect to those guys and
my meter is not showing anything.
Well, I know the secondary should be high,
I believe it's about 10 K or 10 and a half,
so I want to bump my meter up to the
20 K setting which is the closest
setting I have above what I want to measure and
I'm measuring about 10.3k so that's perfect,
that's what the spec is and that's in range.
So that's how you test a dual output coil.
So let's look at one more, a cap coil.
Okay, so here's a different kind of
ignition coil, it's called a cap coil
because it actually sits on top of the
spark plug like a cap so the coil's
all embedded inside this unit.
Same thing as the others, it has a primary and
a secondary coil inside, we can
measure the resistance of both of them.
On a cap coil you'll generally have
two terminals inside a connector,
which I have my meter connected to.
And I looked up our spec on our website,
I know that the primary is very low,
about half an ohm which is what
I'm showing here, zero point four, so that looks good.
And then I wanna measure the secondary resistance,
which is from one of the terminals inside
to the tip that would connect to the spark plug.
So if I connect my meter to it I'm not showing anything.
That's because it's a lot higher than this,
I believe it's about five K or four K.
So I connect my meter to it and
I move my meter up to the 20 K setting,
and now I can see four point four K, which is correct.
So that's how you measure a cap coil,
and I hope this shows you how to
test the different kinds of ignition coils
you might run into on your vehicles.
They're easy to test and easy to
see if they're a problem and you can
go to rmstator.com to replace 'em.