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Test ignition coil?

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Windancer View Drop Down
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    Posted: 25 May 2007 at 12:54am
Is there a way to check an ignition coil to verify
that it is outputting energy to power ignition points?
I have 6.4 volts at the + terminal on the coil (6V system).

As I remember, the coil is to boost the voltage to 10,000 /
20,000 volts? My multi-meter volts scale only increments
up to 1000 ACV.

I am not getting spark out the coil wire that attaches to
center distributor.
Thanks. Windancer
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TERRY Quote  Post ReplyReply Direct Link To This Post Posted: 25 May 2007 at 5:14am
Check continuity through the coil both on primary and secondary sides and chech for short between primary and secondary windings, also measure the resistance in primary and secondary windings.I think those resistances are in the manual..
You can also alternately make and break the primary circuit with a jumper wire and check for a spark from the secondary. That bypasses the distributor and points, because the points, rotor , distributor cap, loss of ground to the breaker plate etc could all cause loss of spark


Edited by TERRY - 25 May 2007 at 5:14am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sean Quote  Post ReplyReply Direct Link To This Post Posted: 25 May 2007 at 7:22am
David:

There is no quick 'n easy "good/bad" test w/only a multi-meter.  It needs to be done on a coil tester, or on-vehicle.  A multi-meter continuity test can tell if it's definitely bad, but not if it's good.
  • Primary side resistance should be 1.2 ohms.  Most meters aren't accurate at low resistances, due to test lead resistance.  Check the resistance of the leads themselves first.  Short them together & read the residual resistance, then check the primary resistance, and subtract the lead resistance.  That should get you close.
  • Secondary side resistance could be anywhere from 3 - 6 Kohms or more, just depends on the make/model of coil.
If either of these reads open-circuit, the coil is shot.
  • If the primary side is much lower than 1 ohm or so, you've probably got a shorted primary.
  • With so many Kohms on the secondary side, it's impossible to know if it has any shorted coils.
The high voltage spark only lasts for brief milli-seconds.  You have to make and break the primary to get spark at all.  As long as current is flowing through the primary, you'll have no voltage at the secondary.  When you break the primary circuit, then you'll have the brief hi-volt at the secondary.

Even if you get spark on a one-shot test, that won't tell you if it will operate at 2000 sparks per minute, or under compression (100psi), or when the coil is hot.  These have to be done under real-life conditions (a tester or on-vehicle).

You might check w/local auto-electric shops, some may still have coil-testers.

Sean




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Post Options Post Options   Thanks (0) Thanks(0)   Quote sudsie Quote  Post ReplyReply Direct Link To This Post Posted: 25 May 2007 at 12:22pm
  
 
 
              My local shop that did my starter & gen, said he didn't have the equipment to test coils?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sean Quote  Post ReplyReply Direct Link To This Post Posted: 26 May 2007 at 6:36am
Originally posted by sudsie sudsie wrote:

My local shop that did my starter & gen, said he didn't have the equipment to test coils?
Yah, and it's a shame.

Most shops just replace it if in doubt.  They make more money that way.  You have the search around, but some of the old time shops still have testers.

Sean
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