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<DIV>If you measure voltage from the distributor side of the coil to ground, you
are measuring drop across the ignition points. If that isn’t near zero,
your points have a problem.</DIV>
<DIV> </DIV>
<DIV>Jim Becker</DIV>
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<DIV style="font-color: black"><B>From:</B> <A title=soffiler@gmail.com>Stephen
Offiler</A> </DIV>
<DIV><B>Sent:</B> Wednesday, November 06, 2019 11:17 AM</DIV>
<DIV><B>To:</B> <A title=at@lists.antique-tractor.com>Antique Tractor Email
Discussion Group</A> </DIV>
<DIV><B>Subject:</B> Re: [AT] Questionable ignition coil</DIV></DIV></DIV>
<DIV> </DIV></DIV>
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<DIV dir=ltr>Voltage drop test only works with current flowing. In the
case of testing the ignition primary circuit, points must be closed.
Voltage drop across coil depends on whether there's an external ballast resistor
in the circuit. If no resistor, a good drop across coil primary terminals
is slightly less than battery voltage. But with a resistor, some of the
voltage drops across the resistor and some drops across the coil. I'm not
sure I can see how this test will tell you much about the health of the coil,
frankly.
<DIV> </DIV>
<DIV>SO</DIV>
<DIV> </DIV></DIV>
<DIV> </DIV>
<DIV class=gmail_quote>
<DIV class=gmail_attr dir=ltr>On Wed, Nov 6, 2019 at 11:16 AM Spencer Yost
<<A>spencer@rdfarms.com</A>> wrote:<BR></DIV>
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<DIV>
<DIV>Sorry to reply to my own message, but I forgot something. Also check
voltage drop. Going into the coil from the ignition switch, you should see
battery voltage. For instance if your battery is putting out 6.2 you should
see roughly 6.2 going to the coil. On the other terminal end of the coil,
there will be a slight voltage drop. However on my bad coil with the
Pacer voltage had dropped all the way to 3.7 from 6.3V. Can not
remember what a good voltage drop is. Surprising large if I
remember right, but not 50%. Maybe I’ll run to the Pacer a little later
and see.</DIV>
<DIV> </DIV>
<DIV>I don’t know electricity or electronics well enough to know how or why
that occurred with reasonable resistance readings but that measurement was the
only out of range number I got.</DIV>
<DIV> </DIV>
<DIV>I got that little tip from Brice Adams and what was the final straw
causing me to get an exchange rather than just continuing to run on the old
one.</DIV>
<DIV> </DIV>
<DIV>Spencer</DIV>
<DIV>
<DIV> </DIV>
<DIV dir=ltr>Sent from my iPhone</DIV>
<DIV dir=ltr><BR>
<BLOCKQUOTE type="cite">On Nov 6, 2019, at 11:03 AM, Spencer Yost <<A
target=_blank>spencer@rdfarms.com</A>> wrote:<BR><BR></BLOCKQUOTE></DIV>
<BLOCKQUOTE type="cite">
<DIV dir=ltr>With an ohmmeter across the two screw terminals, test
resistance. Then test across negative and the coil wire socket.
Make sure you don’t have zero or an infinite reading on either. Any other
reading is highly coil specific and hard to generalize. I
usually see 1-9ohms depending on which of the two tests, voltage, brand,
age, etc.
<DIV> </DIV>
<DIV>However, having said this, I find the tests generally useless as most
coils fail on load and heat and these tests do not rule out these
issues. For instance I once had a Farmall A coil that would die when
hot but tested fine on the bench. A new coil and the tractor purred
all day long for another year or two till I sold it.</DIV>
<DIV> </DIV>
<DIV>Another note: about two years ago I gave the Pacer a
tuneup. Would hardly run. I couldn’t figure it out until,
out of frustration, I put the old coil back on. Ran
great. The new coil tested fine. Fortunately I had
bought the coil from Napa and they exchanged it. The second new one
worked fine and I am still running on it. So you can get a bad coil
out of the box in these days of poor quality analog ignition
components.</DIV>
<DIV> </DIV>
<DIV>I’m sure others more knowledgable will jump in with additional
advice.</DIV>
<DIV> </DIV>
<DIV>Spencer</DIV>
<DIV>
<DIV> </DIV>
<DIV dir=ltr>Sent from my iPhone</DIV>
<DIV dir=ltr><BR>
<BLOCKQUOTE type="cite">On Nov 5, 2019, at 8:19 PM, Gilbert Schwartz
<<A target=_blank>vschwartz1@comcast.net</A>>
wrote:<BR><BR></BLOCKQUOTE></DIV>
<BLOCKQUOTE type="cite">
<DIV dir=ltr>
<DIV
style="FONT-SIZE: 12pt; FONT-FAMILY: helvetica,arial,sans-serif; COLOR: rgb(51,51,51)">I
would like to try and delve into the wide knowledge and expertise of the
members within ATIS. <BR>Is there any acceptable method of determining if
an ignition coil is good short of installing it on a running engine. Our
1949 AC G would not start a few days ago after being parked for a short
period of time. A quick observation determined the contact points were
beyond use. I went to the local auto parts store and was advised I
probably should replace both the points and of the condenser because they
felt like that condenser went first and it caused the points to burn up.
With this information I also purchased a new coil even though I wondered
if the coil was a bad. </DIV>
<DIV
style="FONT-SIZE: 12pt; FONT-FAMILY: helvetica,arial,sans-serif; COLOR: rgb(51,51,51)">Bottom
line; Is there any way to bench test a coil? We have several used coils
laying around here of questionable viability. I would like to pitch them
if they aren't any good. <BR>I appreciate anything you can tell me.
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