In the field, a weak spark condition usually results in ignition coil replacement. However, there’s also the chance of an igniter issue causing poor saturation and prematurely limiting current flow in the coil windings. Rare, but possible, and it’ll burn you if you’re not aware of it. This is where the low amp probe and a lab scope shines during diagnostics.

Engine Performance Diagnostics chapter 1 page 2, 14 - 21

symptoms 50

  • intermittent stall, hesitation, misfire
  • intermittent hard start

fix 50

  • replace ignition coil igniter

test shown enh 50

  • how to use an in-line spark tester to identify an ignition issue
  • how to use a low amp probe to view a coil current waveform
  • how to use a lab scope to view a coil primary voltage waveform
  • analyzing a coil current waveform, identifying current limiting
  • using lab scope triggers during testing

Tools used

  • in-line spark tester
  • Picoscope automotive 4 channel lab scope
  • inductive low amp probe

end faq


(Chapter 22) No Spark Troubleshooting, Ignition Coil & Module Testing

Related videos:

How to test for a shorted ignition coil (Honda Distributor):

Basic Ignition Description, Operation and Testing (any car):

Ignition System Designs, Operation and Testing (an SD Premium video):

Ford 5.4 shorted coil primary winding and bad computer driver:

How to identify a shorted ignition coil (Honda C.O.P.):

end faq

For more information on this topic, I have written a “field manual” called Engine Performance Diagnostics which is available as an eBook or paper book.

Want even more diagnostic training? Whether you are a DIY trying to fix your own car, someone looking to become an auto technician, or a current auto technician that wants to get more into diagnostics, subscribe to ScannerDanner Premium. There is a 14 day free trial.

On ScannerDanner Premium I will bring you right into my classroom at Rosedale Technical College. You will find page for page lectures taken right from my book as well as exclusive classroom type case studies. What is so special about these classroom case studies? I pull live problem vehicles directly into my classroom and we troubleshoot them in real time, using and applying the theory and testing procedures we learn during the classroom lectures. There is no better on-line training of how to troubleshoot automotive electrical and electronics systems anywhere!


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0 # ScannerDanner 2018-01-26 15:08
Quoting Guest:


Post this to my forum brother. We can help you better there and maybe find you a good diagram 
0 # Guest 2018-01-26 13:12
Hello Dan,
Just watched your basic ignition system description. Blown away by your knowledge and ability to simplify components and how things work. You refereed to the set up of coil, igniter, pickup as old style, however, that is exactly what I have in my 1985 Toyota pickup. The original igniter was replaced with the type of igniter in you diagram . Now I understand how it works. Right now I have a no start situation. The key would not make a sound when I turned to start suspected starter.Took it off to test. had 12 volts on the S wire. put it back in and truck started right up first time . tried to start it again started made no sound,had no spark from coil. my book says RELAY. there are only 2 relays, on says emission control? there is no emissions on this truck the other is not marked. Dealer does not know how many prongs the starter relay is. No mechanics around me want to even look at it. Having a dire emergency. I have 1.5 volts coming out of distributor wires with just key on. Need immediate advice. Lives depend on me being mobile.