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A closer look at a coil on plug mis-fire – Auto Repair Chat

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We all to often (myself included) over look opportunities to further our skills and learning. Lets take a closer look at a routine repair in the shop (bad coil swap out) and see what we can learn from it.
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50 thoughts on “A closer look at a coil on plug mis-fire”
  1. Avataaar/Circle Created with python_avatars Andrew B says:

    Hi from Australia. My Toyota with 5vzfe had a bad misfire with unburned fuel smell. I watched this video and learned how to test the coil packs. Pulled each coil and found number 3 had half the resistance of the other 2 on the secondary side (waste spark ignition). Swapped in a spare for the old number 3 and as you would say Mr O. "bada bing bada boo" – misfire gone. New coil on order. Thank you for your channel, I am very grateful to you.

  2. Avataaar/Circle Created with python_avatars Paul Coomer says:

    Thanks for doing all that to teach us !

  3. Avataaar/Circle Created with python_avatars Jeff Smith says:

    amazing explaination!!!!!!

  4. Avataaar/Circle Created with python_avatars houshang saadati rad says:

    Hello .Witch way good to diagnosing car. Do you offer or recommend to take course for diagnosing car please gave me idea. What college or training recommend.

  5. Avataaar/Circle Created with python_avatars JaguarBlack says:

    Man..i wish you 2 can look at my car. It'll be so great just to learn from you.

  6. Avataaar/Circle Created with python_avatars Ginger Sechelski says:

    Remember the good old days you just threw them in the garbage and bought a new one for 15 bucks🤣

  7. Avataaar/Circle Created with python_avatars Antonio Claudio Michael says:

    Very informative video Eric O showing the Primary and Secondary Winding that waveform is going to come in hand. Definitely different than a WaySpark System Nice work as Always Eric O super high Resistance on that bad one 40 plus thousand ohms higher than a good nice Showing why it's bad and comparison to a known good of the same brand as well as known good of different brand @SouthMainAutoRepairLLC

  8. Avataaar/Circle Created with python_avatars Glenn Waren says:

    What if you had a misfire replace the plugs a misfire went away the next day it's back what could it be

  9. Avataaar/Circle Created with python_avatars Turk Ari says:

    I have a chevy silverado 2500hd 02
    Check engine light on security lights on jumping Check engine light, gage cluster no works no speed odometer or rpm, only engine temp gage, when you drive ding ding sounds making me crazy, what I have done in my engine is full tune up ,exhaust manifold gasket replacement, I have p0300 misfires code, my main problem security light and gage cluster since 1a year.
    How I'm driving is I disconnected bmc body modules unplugged so it's not bothering me with sounds, I also hooked up my scanner that's only way I can see my speed gage and all gage is works if I unplug code scanner completely out I don't see nothing works no ligh in the gage cluster ,what would you recommend thanks 😊

  10. Avataaar/Circle Created with python_avatars Charles Downs says:

    what is best coils to use on pontiac grand prix.3.1. se.? ac delco. i think delphi is exact same? i cant get no answer in pontiac club . so i plan on delphi.

  11. Avataaar/Circle Created with python_avatars Shawty El says:

    Great video on board explanation.thanks guys

  12. Avataaar/Circle Created with python_avatars Daniel Silva says:

    Wow! That was a very nice video. Great explanations on terms and what things should look like. I like that you are doing your thing and then you had an unexpected issue happens. It happens to many people and it can be discouraging…. I just change my spark plugs and now I can’t get the truck to idle/lose of power.

  13. Avataaar/Circle Created with python_avatars Dependable Auto Truck says:

    I would have thought that if wire was broken at top the secondary wouldn't build heat to burn it would just charge primary wouldn't be any secondary output

  14. Avataaar/Circle Created with python_avatars Kayla Marie says:

    Great video as always! If we put you two guys in lab coats and hang a chart on the front of that truck and you might as well be two electro cardio surgeons discussing a patient. I am sure to the non initiated who do not turn wrenches it sounds exactly the same. Heck I do wrench and know what's up and it still sounds the same! Dr. Eric and Dr. Ivan lol. You guys are incredibly smart! I learn tons of stuff from you and your videos. Anyone who bitches about why getting your car fixed needs to tune in and watch the processes that take place.

  15. Avataaar/Circle Created with python_avatars Radical HippieTech says:

    yes for sure scope I just seen a bad coil fry computer driver. If the computer would have been replaced with out looking at the scope it would fried the new computer. Snap on has markers for 350 each. Scope scanner and OHm showed a issue. When I change something I need at least 2 things showing it bad not counting symptoms. Great Video as always

  16. Avataaar/Circle Created with python_avatars Roberto Perez Rivera says:

    A very good class keep on teaching, go bills

  17. Avataaar/Circle Created with python_avatars Garage door service says:

    I can’t ever find a goddamn coil pigtail for one of these coils so I guess I’m have to live with a misfire

  18. Avataaar/Circle Created with python_avatars Julius Brown says:

    What wrong when coil pack heat up

  19. Avataaar/Circle Created with python_avatars JD RS says:

    Never buy the aftermarket coil on plugs for your vehicle, when it comes to having to replace these. Always replace them with the OEM brand that came with your vehicle.
    I learned that the hard way.

  20. Avataaar/Circle Created with python_avatars Ricky The tech guy says:

    All ways enjoy your videos

  21. Avataaar/Circle Created with python_avatars Drew Bush says:

    That'll teach you to leave the back door open lol. All we needed was scanner Danner

  22. Avataaar/Circle Created with python_avatars VLS says:

    I like that guy i used too watch him alot

  23. Avataaar/Circle Created with python_avatars \ron cox says:

    yeah i can see how a bad secondary can affect the primary wave form on a scope ,but after swapping coil and knowing the coil was bad why would you even hook a scope to it unless the coil was not the problem, there"s just to many things with these newer cars that cause misfires and you really don"t need a snap on scope just to confirm you need a coil. but i do need a scope ,maybe i can pay for it by charging $$$ for diagnosing bad coils.I learned some thanks

  24. Avataaar/Circle Created with python_avatars Paublus Americanus AMERICANUS says:

    Ivan drew the return back to the plus side of the battery. That would dead short the battery. Did he mean after it went through the battery?

  25. Avataaar/Circle Created with python_avatars Paublus Americanus AMERICANUS says:

    Comes back and punches the primary in the face. Hah so why not just fire? Well no

  26. Avataaar/Circle Created with python_avatars Old Geordie Geezer says:

    Almost 40 years ago I joined the Military and spent 18 months in the classroom learning electronics, and being shown the basics of how Radars and Radios work. This included fault finding and replacing components on boards.
    Imagine my disgust when in the late 80s manufacturing changed towards sealed module replacement.
    While it was almost an insult to my training eventually sealed units won the day and board changing was the way of the world.

    Many years later while working overseas, running an maintenance division in a military organisation, I looked to employ Engineers with the same background as me because I believed a thorough understanding of what goes on inside "the box" was essential.

    The downside of this recruitment policy was that they had an inability to just change the unit and move on, reducing their efficiency significantly.

    The benefit is in identifying WHETHER it works or not. There really is no benefit to understanding HOW the unit actually works.
    If it's dead, change it, move on, next job.

    In finishing – love the videos, just happen to disagree with the requirement for a closer look, other than for personal interest.

  27. Avataaar/Circle Created with python_avatars rehnmaak says:

    The oscillations are actually a result of the capacitance in the circuit possibly parasitic capacitance in the coil oscillating with the coil inductance basically a classic LC resonance circuit.

  28. Avataaar/Circle Created with python_avatars Gordon says:

    I was doing some of the same measurements in 1960 using an old heathkit scope.

  29. Avataaar/Circle Created with python_avatars R. B.L. says:

    A Note:
    Bought the Autel MK808 and it actually does have a misfire counter for dodge, just saying.

  30. Avataaar/Circle Created with python_avatars Darren O'Gorman says:

    Excellent work guys!!!

  31. Avataaar/Circle Created with python_avatars eyesalooking says:

    Good stuff. Well explained even for a beginner like me. I only wish that I had the Snapon Scanner. I just got the Launch 126E as my first scanner. It doesn't detect any misfires on a 2003 Ford Focus that is running like crap. I just purchased an in-line spark checker for recessed plugs that can also test coils. Hope it helps figure what is going on.

  32. Avataaar/Circle Created with python_avatars robert boykin says:

    Used to be about 1K ohms per inch [ plug & coil wire]

  33. Avataaar/Circle Created with python_avatars Spartacus says:

    You know, I learn a lot from your videos (thank you, btw) but I’ll know how to use a verus and not have one, lol

  34. Avataaar/Circle Created with python_avatars Chip Burns says:

    I get a random misfire at idle always but When I start the car I have a dead cylinder for about 20 seconds then its fine. I replaced the cop’s and plugs but no results. I also forgot to screw in two spark plugs but found out once I started it lol. What do you think is a good way to find the misfire?

  35. Avataaar/Circle Created with python_avatars northpostman says:

    Whether or not the primary and secondary windings are connected depends on coil design. If they are connected as Eric and Ivan have illustrated here then the coil is "Married" or it is a tapped transformer design. If they are not connected, it is called a " Divorced" or a true transformer coil design and relies completely on mutual induction between the coils. In the case of a "Divorced" coil, the second leg of the secondary winding would be connected to another spark plug as this is the design used with waste spark systems. The "Married " coil design is used with conventional and COP type coils. In either case, the path to ground for the secondary winding is across the gap of the spark plug. The primary side of the coil will have ignition feed not battery at the positive terminal, the negative side of the primary winding will be grounded by a transistor in either the PCM or ICM depending on system design.

  36. Avataaar/Circle Created with python_avatars Gladmar Chatlein says:

    Nice demonstration guys..very educational !
    I apprecited so much the drawings and explanations on the white board.
    Thanks for your efforts guys.

    Blessings for you guys !

    👍😎

  37. Avataaar/Circle Created with python_avatars Michael Knorr says:

    The second leg on the secondary circuit goes to ground. The magnetic field in the secondary circuit excited the current ti the point that it can flow through the gap in the spark plug also.

  38. Avataaar/Circle Created with python_avatars Michael Knorr says:

    The physical wire from the coil secondary to the contact to the plug has a break. Coil saturation voltage is high. Enough to jump, but it goes to ground in the system.

  39. Avataaar/Circle Created with python_avatars Shane Harrison says:

    Cool work both of you and its info well used and saveing the wave forms is a good idea to help in diagnosing

  40. Avataaar/Circle Created with python_avatars Scott Craft says:

    Hey I just been watching like every day! You guys are awesome down to earth people that you don't see every day. I am a dodge ram 1500 man and I haven't see to many vids on them. Just because they don't break down like the foreign car do lol.

  41. Avataaar/Circle Created with python_avatars Ridge p says:

    Can a weak plug wire cause a PO353 on a 2005 Ford Taurus 3.0 new 6 wire coil module? Good spark at coil post, little weaker at plug end of wire?

  42. Avataaar/Circle Created with python_avatars Ridge p says:

    Great info guys! Both guys are smart!

  43. Avataaar/Circle Created with python_avatars Old Geordie Geezer says:

    Sorry Eric, but your pal Ivan doesn't contribute positively to your videos. He has an arrogance that just makes me want to look for something else.
    It summed him up perfectly when he referred to swapping coils as "caveman diagnostics", then when you corrected his reading of the resistance of the coil and his response was "whatever!"

  44. Avataaar/Circle Created with python_avatars Tome oftheAncient says:

    Interesting video but for me there are too many cooks in the kitchen.

  45. Avataaar/Circle Created with python_avatars textbook2o11 says:

    This is really an exceptional video. Great combination of engineering and practical knowledge. Thanks for sharing your wisdom.

  46. Avataaar/Circle Created with python_avatars Freddy Flintstoned says:

    Densoless. hahahahahaha

  47. Avataaar/Circle Created with python_avatars Albert's Auto Diagnostics LLC says:

    Please do more picoscope videos im a new user trying to learn thank you 🙏

  48. Avataaar/Circle Created with python_avatars Paul Yuricek says:

    For those of us who do not have an oscilloscope is there a way to check those coil packs? With a DVM possibly?

  49. Avataaar/Circle Created with python_avatars lhoanii says:

    I have really tried to like Ivan. Initially, he kept interrupting Eric which annoyed me. He seems a little more respectful in these later videos. There is something about Ivan that I simply don't like. Oh well, good video for c.o.p. ignition short.

  50. Avataaar/Circle Created with python_avatars bill massey says:

    bad coil. problem was figured out. no further talk was necessary. I know this is an old video. do your diag. replace coil. move on.

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