How To Quickly Diagnose The Sneaky Weak Ignition Coil

A quick video to rule out or confirm a weak ignition coil, the symptoms of which present themselves as a fuel delivery issue.
I filmed the spark of a weak coil and a good strong coil which in person you can visually see the difference, but the differences are very subtle and hard to see in the video. So when checking to see if you have spark with a weak coil, you'll see that you do indeed have spark, but under load the spark isn't strong enough to keep up with increased fuel/air mixture and the engine bogs down or quits above idle under load. I'll show how the engine has a hard time starting and running with the weak coil, but immediately starts and runs strong and smooth with the good coil.
I describe the symptoms and behavior of the weak coil, so if you're experiencing these symptoms swap out the coil which is quick and easy to just jumper one in. You'll quickly rule out or confirm a weak coil. If it's not the coil, it's time to check fuel pressure, and fuel filters, or run circuits in the carburetor.

[@mosessich2163]

Thank you for the video! I am just starting to work on my own vehicles since I am only 17. I always appreciate when people share decades of experience!

[@mkdhdinfiniteendlessconten3873]

Hi. This is instantly and easily the most meaningful comment and compliment I've ever received. You will go far and do well in life with your outlook. I'm getting close to having 100 videos now, mostly on DIY/How to across many topics. I'm also working on and currently posting a series of videos from my Route 66 Trip in my 1974 Oldsmobile Cutlass Supreme. I even have How to Make Cold Brewed Coffee, Setting Up a Floyd Rose Bridge on a Guitar, and Changing Batteries in Old iPods and Tablets. While I might be showing "how to" do a particular task, I'm also teaching skills, methods, techniques and basics that apply to many situations you'll encounter. Go to my channel home and poke around, and you should find numerous videos that will help give you a good foundation. Some of my first videos are on doing a budget build of a Ford 302. I just loaded two-part series on the Ford AOD Transmision Rebuild. I hope to be doing an updated engine build video sometime soon. I look forward to seeing and hearing more comments from you. I wish you the best. Ask me anything any time. I'd be interested to know what you might be working on and assist you on your journey. :-)

[@garrettpolzin7235]

I’ve been trying to find a “fuel issue” for 3 weeks. I cannot wait to test my coil I have a pretty good feeling this is issue. You described my exact issue

[@mkdhdinfiniteendlessconten3873]

Hi. Thanks for watching and taking the time to comment. Ya, a weak coil that breaks down under load will give the same/similar symptoms as fuel starvation. You can ohm out the coil statically and it will appear to be fine since it's breaking down under load dynamically. Generally if you work on cars, you have known good coils on your shelf. It's a good idea to grab one every now and then when in the junk yard. I have a recent video regarding fuel starvation again with essentially the same symptoms which turned out to be a bad in line fuel pressure regulator. With fuel starvation the engine will often stall if you don't back off quick enough. With a weak coil the engine will stay running and bog down, but rarely stalls and will come back once you let off the gas. Anyhow let me know how it goes and if it was indeed the coil on your vehicle.

[@kennethhettig883]

Great way to test a coil, thanks for posting!

[@mkdhdinfiniteendlessconten3873]

Hi. Thanks for watching and taking the time to comment. This is one of my highest viewed videos, and seems to have helped a few folks out which is the whole point. One person who I know personally was experiencing these symptoms watched it, swapped the coil and problem solved. Bottom line, easiest way to test a coil and rule also out a fuel system problem is just swap the coil. Thanks again for watching.

[@GoatPilot04]

Small pro tjp for anyone here looking for help: For any older electronic distributor ignition, long wires w/ single coil, etc, do this at night or in your garage with the lights off. After you get it running, also check under the hood in the dark for any spark/ignition leaks arcing around the engine from bad/damaged wires, loose connections, bad/damaged/loose boots, damaged/burned through coil, etc.

[@mkdhdinfiniteendlessconten3873]

Hi. Thanks for watching and taking the time to comment. Yes indeed on checking for HV Leaks in the dark. It's less of an occurrence with modern plug wires. Used to be regular thing that plug wire insulation would break down after a year or so. A spray bottle of water lightly misting the system will really make the electrons put on a show and confirm the plug wire insulation is breaking down causing misfires and skips.

[@eddieconerly1222]

This is it from New Orleans please more content your delivery is awesome your info is great tell us more about your truck or you keep it running good so I can learn from you thanks

[@mkdhdinfiniteendlessconten3873]

Hi Eddie from New Orleans. I think you're my biggest fan. If I had a fan club, you'd be president. ;-) That's a great idea on the truck, so I'm going to do it as soon as the weather warms up with some longer days. I appreciate the compliments regarding my content and how I deliver it. I enjoy doing such things. There's a big cult following for The Bull Nose F-150's. They had a new cool look that was aggressive just like the body style before them, and much cooler than the styling changes they made after this version. As beat up as my truck looks, I get offers for it constantly. It's my daily driver. Except for a brief time, I've owned the truck since 1991 and it played a big role in my life taking my family and I on many adventures and hauling and towing many things many miles. I always tell everyone "I love that truck so much I bought it twice" which is actually true. It even survived a tree falling on it during a hurricane and has the battle scars to show it. I'll be doing body work and panel replacement on the cab, replacing/fixing/upgrading the A/C, building a new cool engine. The interior needs a lot of work. It originally had an awesome cloth bench seat, and the dude I temporarily sold it to replaced it with buckets, that are sort of ok as they open up the center hump, but they need reupholstering. I'm on the hunt for some vintage 70's Thrush Side Pipes for it and will be putting those behind a good set of long tube headers. The relatively new foreign made fuel pump is leaking oil at all the crimps and seams. I'll be doing a video on that in the next few days, so stay tuned. Thanks again.

[@barryallenporter8127]

Good video. I always forget the simple things and overcomplicate issues.

[@mkdhdinfiniteendlessconten3873]

Hi. Thanks, and thanks for taking the time to watch and comment. This problem is easier to diagnose on lower energy points ignition system since the coil output was lower and the plug gap smaller. it was more frequent in older style coils. HEI has a higher output and larger gap that even a weak coil will still jump. The importance of plug gap is you want the largest gap possible that the spark will jump. The larger the gap, the hotter the spark and the better the initial combustion of the compressed fuel/air mixture.

[@michealphy4013]

My HONDA CIVIC 1985 . took me 1 month been through 2 garages unable to diagnose the problem . Thanks alot for this information

[@mkdhdinfiniteendlessconten3873]

Wow, an 85 Civic! That's awesome that you're keeping it running. Great simple economic fun car. Glad my video solved your problem and helped you out. Thanks so much for watching and taking the time to comment.

[@nelsonluke-se2xp]

Thanks for that I'm leaning for coil symptoms.

[@mkdhdinfiniteendlessconten3873]

Hi thanks for watching and taking the time to comment. Ya, it's rare, but a weak coil will taunt you. in 50 years I've probably only had 3 weak coils, and never a dead one. It's quick and easy to rule out if you have these symptoms so it make sense to rule it out or confirm it before messing with fuel system stuff.

[@ryantabussi7180]

extremely helpful and good explanation thank you very much

[@mkdhdinfiniteendlessconten3873]

Hi. Thanks for watching and taking the time to comment. Hope the video helped you out.

[@ReedMJones]

Excellent Symptoms Description! Thank You.

[@mkdhdinfiniteendlessconten3873]

Hi. Thanks for watching and taking the time to comment. Thanks for the positive feedback. Hope the video was helpful for you. :-) Take a look at the rest of my videos when you have a chance. Might be something else of use for you. Thanks again,

[@melvis2017]

Thanks for the great job very good explanations and the great humor Thanks again for sharing with us all 🇩🇰👍

[@mkdhdinfiniteendlessconten3873]

Hi. Thanks for watching and taking the time to comment. Hope the video was helpful and glad you enjoyed my humor. I've got quite a few other videos on a variety of subjects that you might also enjoy. Thanks again.

[@melvis2017]

@@mkdhdinfiniteendlessconten3873 thanks for that plz more vidéos

[@TheJaredsalinsky]

This is very helpful. My ‘78 carbureted Ferrari is having that same ‘chugging’ and ‘hesitation’ when starting. And it takes a few times to get it started. Sounds exactly like your Ford! Can you ‘fix’ coils? Or clean them? Or do you just have to replace them? Thanks!

[@mkdhdinfiniteendlessconten3873]

Hi. Thanks for taking the time to watch and comment. Coils are not repairable. They're also filled with oil for cooling, of which old vintage ones had PCB's in them. A weak coil will also cause the exhaust to have the same nasty smell as when a gasoline engine "Diesels" when cut off and continues to run "very badly". It's similar to dieseling as the spark is so weak the fuel mixture barely ignites from the spark. It's quick, cheap and easy to see if it is indeed a weak coil and resolve the issue or rule it out and take a close look at carburation (I think your model is carbureted) and or ignition.

[@TheJaredsalinsky]

Thank you

[@Thunderbird1968]

Very helpful video, thanks

[@mkdhdinfiniteendlessconten3873]

Hi. Thanks for watching and taking the time to comment. Glad it helped.

[@gregander1241]

I don't know about that spark color issue, however there may be a difference between the two coils in terms of voltage.

[@mkdhdinfiniteendlessconten3873]

Hi. Thanks for watching and taking the time to comment. The spark color is kind of subjective as it has both purple and orange/yellow "aura's". I might have mixed them up when describing. Usually more purple is a higher voltage. Was just using that as a visual aid. Main point is that a weak coil will give fuel system symptoms. Only takes a few minutes to rule out jumping in a another coil. A friend of mine who works on modern computer controlled vehicles but has one older truck was having symptoms like I describe in the video watched this video and solved his problem in minutes after he'd been scratching his head for a while, being used to OBD Scanners and Fault Codes.

[@eddieconerly1222]

Man this is Eddie in New Orleans this is the second time you didn’t help me I have a 83 4150 you help me with the gas tank and now you help me with the coil cause my truck is doing the same thing that you describe thanks

[@eddieconerly1222]

👍

[@mkdhdinfiniteendlessconten3873]

Hi Eddie. You had me worried there at first due to a typo in your comment: "second time you didn’t help me", but I think that was supposed to be "Second time you did help me." Probably AutoFill filling in the wrong words. Hopefully that's the case, and glad my videos are helpful. That's my goal to educate and help, and eventually gain enough subscribers to have an income from this. Thanks again for watching and taking the time to comment. Stay tuned, lots more content on the way.

[@hammerhead19able]

Thank you so much!!! I think now I don't have to push it into the parking lot by the mall, helping my son.😂😂😂

[@mkdhdinfiniteendlessconten3873]

Hi. Thanks for watching and taking the time to comment. Can't tell for sure, but sounds like my video helped you out. Let me know if you have the time. Thanks

[@cbscherger9861]

It'd be interesting to see the difference in primary & secondary resistance between the 2 coils.

[@mkdhdinfiniteendlessconten3873]

Hi. Thanks for watching. I'll have to see if I still have that bad coil. Generally I have found that unless the windings are either shorted or open, that ohming it out is not a definitive check. The resistance range for an acceptable coil is wide and for the primary very low ohms. It lets you know you have a ratio of resistance from primary to secondary and that it will step it up. If it's breaking down under higher rpm it will still Ohm out ok and have you chasing fuel problems that aren't there. I'll see if I still have it and if so I'll put the readings in a subsequent comment. Thanks again for watching and taking the time to comment.

[@StephenPudumo]

Good.and.profitable.thanks.keep.it.up❤❤❤

[@Noliftracingbro]

Gotta 95 mustang gt it's doing the same thing I already have a new pump and assembly haven't put it in yet... And a new coil gonna try the coil in the morning

[@mkdhdinfiniteendlessconten3873]

Hi. Thanks for watching and taking the time to comment. Let me know how it goes. I think on a 95 the coil is part of the distributor if it's still a factory set up. Many people strip the EFI off and convert to a carburetor and put some sort of aftermarket Electronic Ignition like a Pertronix or MSD with a separate High Energy Coil, so I'm curious as to what your setup is. Anyhow, it will take minutes to rule out the coil and it is often the case. A friend of mine with a 6 cylinder 90's Ford was getting sort of stranded with an intermittent loss of power over 2,000 rpm and having to limp along, watched my video, tried the coil, and solved it. Let me know how it goes.

[@freshbutplain1144]

What if it’s backfiring? Could a bad coil cause that?

[@mkdhdinfiniteendlessconten3873]

Hi. Thanks for taking the time to watch and comment. It's possible if you're also experiencing that loss of power at about the same throttle point. If you're power is good check your timing that it's not too far advanced or jumping around from a worn distributor or worn timing chain. What you're thinking is a backfire could actually be a "Lean Pop" in the carburetor or a vacuum leak. If you carefully/lightly cup your hand over the carb and the RPM's pick up you probably have a vacuum leak which could be worn throttle plate bushings. Throttle plate shaft will wiggle around. A worn accelerator pump in the carb will cause it to lean pop, not giving that squirt of fuel it needs when you open the throttle to overcome the temporary lean condition of opening the throttle. Check those things and let me know.

[@waynecox5206]

Thank you brother i am trying to fix my 60 classic ford i am stumped its doing exactly what you described so im thinking faulty coil

[@mkdhdinfiniteendlessconten3873]

Hi. Thanks for watching and taking the time to comment. You can jump another in with some clip leads and know instantly if it is a weak coil. Mine has the slide on terminals so its a quick connection. If they're held on with nuts then it takes a few more mins to jump it in. Just make sure at least one lead is fully removed if jumping another one in to see if that's the problem. Let me know if it was the coil.

[@manwar999]

thanks

[@mkdhdinfiniteendlessconten3873]

You're welcome. Glad you found it helpful.

[@dylanjames4537]

Off to the parts store, my dads 1981 xd ford falcon with a 351 Cleveland electronic ignition coil just died😅 it gives blue spark off the plug has fuel but will not even cough the car ran perfectly when last parked up. So new coil before i get any further with the ignition system.

[@mkdhdinfiniteendlessconten3873]

Hi. Thanks for watching and taking the time to comment. The coil in this case is a sensible component to rule in/out and easy to swap out. The spark color can be hard to judge and doesn't come across true on the video, and honestly a blue spark is actually hotter. I was in a hurry doing the video and mis-spoke. Anyhow, it does sound potentially like the coil as having spark if it's not hot enough is essentially the same as no spark. Sounds like the ESC is working, so if you have the right amount of fuel (as in it's not too much and flooding) it's pointing towards the coil. This video has helped quite a few folks, so hope this solves your problem. Let me know if it was the coil.

[@dylanjames4537]

@mkdhdinfiniteendlessconten3873 brought a new coil about to test now.

[@dylanjames4537]

@@mkdhdinfiniteendlessconten3873 it was the ignition coil as suspected mate. Thanks.

[@mkdhdinfiniteendlessconten3873]

Yay!!!! Great news. So glad I made this video. It has helped quite a few people. Glad you're up and running again. Hopefully I've earned your subscription. ;-) Thanks again for watching.

[@aopspot4691]

I have a 1983 351 and when I start it up it idles high im guessing for the choke but when I give it gas to take the choke off it idles rough and stals

[@mkdhdinfiniteendlessconten3873]

Hi. Thanks for taking the time to watch and comment. Nice you've got an 83 with a 351. It's not the coil. Sounds like a vacuum leak or you're missing a cylinder which a high idle will mask and can also be caused by a vacuum leak. Your curb/base idle could also be set too low or mixture too lean. Cup your hand over the carb when you kick it down. If it picks back up it indicates too lean of a mixture which can either be a vacuum leak or your mixture setting. Check all your vacuum lines. My guess is they're old, so probably cracked. I'd plug them all coming from the carb including the Booster and PCV valve and see what it does. Your Booster could have a bad diaphragm and be leaking. If the issue goes away it's a bad hose or whatever the hose feeds has a leak. There's probably a vacuum tree on the back of the manifold that feeds several accessories like the AC/Heat and EGR Valve. (Oh ya EGR Valve could be stuck open). Some of those ports are extra and have rubber caps which will rot and fall off. Make sure every port is plugged. Point an infrared thermometer at each exhaust port on the exhaust manifold. If a cylinder is dead it will have a much lower temp. A vacuum leak on an intake runner that feeds that cylinder will cause it to lean out and not hit. If the throttle bushings are worn you'll also have a leak that's hard to find. Wiggle the throttle linkage lever. If it moves around it's worn and leaking. Let me know what you find out.

[@dellgregg4663]

Would this cause my truck to run rich? Carb is rebuilt and tuned. Trying to diagnose my running rich and taking forever to start.

[@mkdhdinfiniteendlessconten3873]

Hi. Thanks for watching. Very possible. Takes seconds to jump another one in to see. See if you can find one in junk yard for $5. New ones are $30. If it's HEI Electronic Ignition you'll need that type of coil. If it's points, a lower output coil, which in 2024 you're not going to find in a junkyard. Since you said it's running rich it's likely the fuel pump is putting out too much pressure. Measure it. Should be 5 - 6 PSI. Anything over is too much for the needle/float. I have numerous videos on this. Go to my channel home and you'll find them. Let me know.

[@cyrilgoulding9668]

I'm getting 9 volts to coil but nothing from it so bought a replacement and still no spark don't no what to do next as can't get engine started

[@mkdhdinfiniteendlessconten3873]

Hi. Thanks for watching and taking the time to comment. Is this an older ignition system that uses an External Resistor? What is the Key Position when you measure at the coil? Older systems prior to HEI Electronic Ignition put 12VDC across the Coil Primary with the key turned all the way to Start/Crank with the Starter Engaged. Once you bring the Key back to Run, the Voltage at the Coil is approximately 9VDC, so if you're measuring at the Coil with the Key in Run it would Normally read 9 VDC. What is the Year/Make/Model/Engine? What type of ignition? Points or Electronic? When you have no High Voltage Spark out, first thing to check is that you have a pulsing 12VDC in to the Coil. The Coil is a Step Up Transformer which requires an Alternating Current (AC) going in to function. Collapsing Felds in the Primary induce a Magnetic Field into the secondary which has more windings and steps it up over 20KV. Since a Car is DC, a pulsing DC (On/Off) in the primary as the result of Points opening and closing or a magnetic pickup into a control module produce a pulsing DC from the Distributor to the Coil. If you have points, its easy to visually (and Audibly) test this. With Cap off and Coil output grounded grab the rotor and rotate wiggle it back and forth. IT will only move a little against the advance. If the Distributor cam is close enough to allow the points to open and close, and the points are properly gapped you'll see and hear a little crackle when they open. With electronic you wont see anything, in the Dist, but will hear a pop and see a spark if you have the coil wire positioned close to the manifold. Let me know what you have and the results of what you try.

[@cyrilgoulding9668]

@mkdhdinfiniteendlessconten3873 thanks for replying, my car is a 1984 rover sd1 2300. With the key turned fully but not turning over im getting 9 volt I've check for a spark but nothing I thought was the ignition coil so bought a new one but still nothing coming from coil even thought 9 volts to it so I'm kinda stumped

[@mkdhdinfiniteendlessconten3873]

That car has Electronic Ignition, so the Ignition Module in the Distributor is what creates pulses to the coil. It's also a Lucas Electric which on it's best day is the worst system. I'm assuming that by 84 they were running Negative Ground. Lucas (British Cars) ran a Positive Ground possibly into the 70's. The Coil with the Key on puts a steady hot to the Pos side. You should be reading from the Pos side of the Coil to the Intake or some unpainted ground on the Engine. Don't read across the coil. In Run the Hot side of the coil would typically read 9VDC if it has an external Resistor. The Neg Side of the Coil is what get's the make/break pulse from the ignition module in the Distributor. It's highly likely that the Ignition Control Module in the distributor is bad. I can't guarantee it w/o directly troubleshooting it. There may be info online as to how to ohm out and check the module to confirm it's bad. You'll have to order that module on line. No one will have that locally.

[@vishallotey2053]

My royal enfield bike has starting problem And it stops during idling. Could it b a weak ignition coil ?

[@mkdhdinfiniteendlessconten3873]

Hi. Thanks for taking the time to watch and comment. That's sounding more like air/fuel mixture with the carb which when cold is controlled by the choke. Couls also be a vacuum leak after the throttle valve. If it smooths out cupping your hand over the carb, there's a vacuum leak. Weak will generally start ok-ish, although the one I showed was getting slow to start. If the bike is ok once it warms up, it's mixture. The weak coil will drop out consistently at the same speed/rpm under load and come back if you let off.

[@vishallotey2053]

@@mkdhdinfiniteendlessconten3873 thank u sir for the reply.will check all once again

[@ClaytonroystonDeKlerk]

I have a 1983 model prelude spark plugs will also keep fouling with bad distributor coil and when I try to take off engine feels like about to stall

[@mkdhdinfiniteendlessconten3873]

Hi. Thanks for watching and taking the time to comment. Was the coil the whole problem with the lack of power and plugs fouling?

[@ClaytonroystonDeKlerk]

@@mkdhdinfiniteendlessconten3873 yes how are u I do believe the coil is the cause for spark plugs fouling everyday also the car lights goes from bright to dim when rpm drops to 800 rpm and goes bright when idling at 1000 rpm I believe the alternator is also bad the spark plugs will smell like fuel on it when coil is bad and loss of power also misfire

[@mkdhdinfiniteendlessconten3873]

ah, the plot thickens. With these other symptoms it sounds more like the charging system is the root cause. The coil is actually a transformer that steps up the pulsing input which simulates an AC voltage from 12V to 20,000 and up to jump the gap in the plugs. If input drops, output drops proportionally with a weaker spark that will not jump the plug gap. The battery is used to start the engine. After it's running the alternator takes over. If the alternator is self exciting and functioning properly you can take the pos cable off the battery while it's running and the engine will keep running. Check your voltage with it running. Right after the engine starts and for some time after as it recharges the battery from the stress of starting, you should have 14.2 VDC at the battery. As the battery charges, the voltage will drop to 13 or so, but should always be over 12.6. Each cell is 2.1Volts. Check the running voltage first. There are other things to consider, but first rule out or otherwise fix the charging system if it is indeed not putting out the required voltage.

[@ClaytonroystonDeKlerk]

@@mkdhdinfiniteendlessconten3873 thank u for your advice i will replace alternator and coil i think it should run better after that

[@mkdhdinfiniteendlessconten3873]

You should check the voltage while it's running with a voltmeter as I described above. Takes less 5 seconds. No point replacing the alternator if it's good. Let me know. Curious to find out the cause.

[@danmichans]

I have a 88 F150 that will run about 20 minutes and then chokes out and dies got both new fuel pumps and fuel pump on the rails new, wondering if this could be my issue I put new plugs wires and cap on as well

[@mkdhdinfiniteendlessconten3873]

Hi. Thanks for taking the time to watch and comment. The symptoms are leaning in that direction after going through the fuel pumps unless of course the 12V to the pumps is dropping out due to corrosion or a relay letting go. Getting back to the coil, that is a typical symptom of a weak/failing coil breaking down, and it's quick to rule out. A friend of mine with a late 80's (might be 88) F150 was experiencing similar intermittent symptoms and had been through the fuel system watched this video and scratched his chin with a Hmm, swapped out the coil, and got rid of the problem. Again can't say for sure your problem is the coil (could be ECM) but it's cheap enough and quick enough to try to either fix it or rule it out. I by training generally don't shotgun try things hoping to fix it. I measure, inspect, determine the cause, then replace or resolve whatever it is. There are instances though when a symptom is so intermittent or specific that w/o having fuel pressure gauges, HV probes measuring coil output, scopes reading ignition signals while under actual use (most of which is impractical) that you have to resort to "trying something" that could reasonably be the cause. Let me know.

[@stevehunt3847]

Hi i have a coil its old primary reading is 0.4 but secondary reading is 1 ohm ..im sure it needs replacing its very old

[@mkdhdinfiniteendlessconten3873]

Hi. Thanks for taking the time to watch and comment. With those low readings, I'd say that coil is effectively shorted.

[@stevehunt3847]

@@mkdhdinfiniteendlessconten3873 thanks the secondary reading jumps from 1 ohm to 6 ohms on 3 different test I reckon coil is shorting out

[@mkdhdinfiniteendlessconten3873]

Hi again. For what it's worth, ohmming out a coil (actually a transformer full of oil for cooling) is somewhat of an exercise in futility. A baseline rule of thumb is the primary to secondary resistance ratio is 1:100, but that varies by application. In the 1960's - 70's you could for the most part swap coils between Ford/GM/Chrysler within types that used Internal or External additional in line series resistance. When cranking/starting, full 12 volts was applied to the coil. When the key went to Run it switched in a series Ballast resistor and dropped the voltage across the coil to about 9VDC. Running straight 12VDC to the coil will burn it out. On the other hand if you switch to a Pertronix Flame Thrower and Electronic Module to eliminate the points, it does require 12VDC at the Coil. So getting back to the "Futility of checking resistance", the resistance range coupled with the 1:100 ratio that your coil is reading 0.4 Ohms on the primary could theoretically be "good" if the secondary reads 400 ohms. Since yours is reading 4ish Ohms on the Secondary that does indicate a shorted secondary. Basically Ohmming the coil checks continuity. To know for sure, just swap it. Even if a coil checks "good" via resistance, the Ohmmeter is a low level static test. It's running a very low current through it and low voltage across it which can't detect insulation breaking down and windings shorting at 12,000 Volts.

[@DG-od4si]

nice video, thanks

[@mkdhdinfiniteendlessconten3873]

Hi. Thanks for watching the video and taking the time to comment. The spark visual and sound difference didn't really show on camera, so was disappointed in that. For real life troubleshooting you're just going to jumper in another one to confirm or rule out the coil. Jumpering in a coil takes just a few minutes. It's less than a minute on one of these slide terminal connections. Takes a few more minutes on a nut terminal connection. The HEI GM coils built into the cap are quick and easy too. If you have spark and similar symptoms to what I describe, jump in a known good coil and confirm a bad coil, or rule it out. If it's bad, then you can deal with that annoying wrap around mounting bracket if it's an intake manifold mounted coil. Otherwise move on and take a closer look at fuel system and carburation.

[@DG-od4si]

@@mkdhdinfiniteendlessconten3873 thanks again. i order that tool and this will help me to find which one of the 6 pencil coils are the sneaky, not working right

[@gregander1241]

what about spark advance? How do viewers know if he did'nt tinker with that?

[@mkdhdinfiniteendlessconten3873]

Hi. Not sure I understand your comment, but to verify timing and spark advance, just use a timing light and see where your initial timing is and total timing after increasing RPM. Try it with and w/o vacuum hooked up to the advance so you know how much of the timing is from the vacuum. Make sure and plug the vacuum line coming from the source. Probably should never have a total timing at high rpm over 36 degrees. Keep it under that. Again, not sure if I understood your comment. Hope my response was helpful. Also watch Thunderhead289 and Uncle Tony's Garage.

[@gustaveiserner6743]

Air gap for ignition testing outside of engine should be 7 mm , third of inch minimum. Air gap testing device available .

[@mkdhdinfiniteendlessconten3873]

Sorry for the delay. Good info. Thanks for adding that to the comments.

[@raymondrios7946]

on my 1978 f250 i can remove the spark wires from the distributor without getting a shock with the car on

[@mkdhdinfiniteendlessconten3873]

Hi. I get zapped every time on any car always. To avoid that I wear welding gloves and use insulated plug wire pulling pliers, and pre pull the wires at the cap and stick them back in loosely so I can pull the suspected ones quickly and easily. Otherwise, it's ZAP, for me anyhow. lol I use an infrared thermometer on the exhaust to find cooler cylinders and then know which wires to pull to see if there's a difference, then know where to check compression.

[@raymondrios7946]

sorry i did not finish asking the question Being able to do that will mean that I have spark problems Excuse me, I'm using a translator

[@aolegario1]

Hotter is blue/purple, weaker is orange/yellow brah

[@mkdhdinfiniteendlessconten3873]

That seems logical and what I was expecting as I weld and a high voltage arc is generally blueish, but I saw the opposite ehen comparing them. My main goal was to educate that a weak coil will give fuel delivery symptoms, and it's so easy to swap a coil and rule it out to try that first. Thanks for watching and taking the time to comment.

[@whitecracker4012]

going to give this a shot on my 91 maxum

[@jdg3079]

How about if its heating up?

[@mkdhdinfiniteendlessconten3873]

Hi. Thanks for watching and taking the time to comment. The coil will normally be warm, but not hot. If the coil is getting Hot, either the primary winding is developing shorts between windings, or depending on your year and setup, could be getting over voltage. Up until sometime in the 70's if I recall, most starting/ignition circuits put 12 volts to the coil with the key in the start position, and then in the run position the hot to the coil ran through a ballast resistor in one form or another dropping the voltage to 9 Volts to the Coil. My older GM cars have two wires to the coil hot side. One for Start and One For Run. If it's an older car many hands have been messing with it over the years. Often times people have rewired and run straight 12 to the coil not realizing this will burn up coils not intended for straight 12V. My 83 Ford takes straight 12. When I convert points distributors to Pertronix with a Flame Thrower Coil, they get straight 12V. Measure you voltage at the coil from Hot to ground (not across) and see what it is. Check the primary coil resistance with the wires disconnected from the Primary. If I recall, it should be 4-8 Ohms, but I need to check and confirm that value. What is the car/truck in question?

[@barry8642]

Good production the build up nice and slow for second coil then the twist it looked the same 😮 what??? You should try the entertainment industry it's worth it

[@mkdhdinfiniteendlessconten3873]

Hi. I think you're referring to how the spark looked. Ya on camera after I played it back they look the same which was disappointing. In person directly viewing there was a noticeable difference, but in the end one coil is good, and the other breaks down. Fun Fact: As far as what your eye vs a cell phone camera sees, did you know you can use the camera to tell if a Remote Control is working? Look through your camera screen while pointing the remote at it with a button pushed. If the remote is working you'll see quick faint light pulses. Must be frame rate etc. Can't see it with the naked eye. Thanks for watching. Peace.

[@barry8642]

Weak not all the way bad that's from ? Windings insulation getting compromised maybe

[@mkdhdinfiniteendlessconten3873]

Hi again. Not exactly sure, but suspect something like that. I think it's frequency related which affects the "Reactance". Higher RPM = Higher Frequency. An automotive coil is actually a Step Up transformer with a Primary and a Secondary and is a Reactive Component with "Reactance" (resistance that's only present when subjected to AC) which varies with frequency: XL=2piFL. XL is Inductive Reactance, pi = 3.14, F= Frequency, and L=Inductance measured in Henries. From the formula you see that Reactance is directly proportional to Frequency in an Inductor (Indirectly in a Capacitor). AC is simulated in an automobile with a pulsing DC. When the DC is applied, and then removed, the back EMF induces a voltage in the secondary which has more windings greatly stepping up the voltage. If the insulation on the windings which is a thin chemical coating breaks down, it shorts between windings while operating. The coil will ohm out ok since the Ohmmeter is applying very low DC. The resistance range to check a coil, both primary and secondary is wide. Unless the coil is open or shorted checking it with an ohmmeter is not conclusive. Thanks again for watching and taking the time to comment.

[@billyganoesr6546]

I thought a blue spark is a hotter spark than an orange spark

[@mkdhdinfiniteendlessconten3873]

Hi. Thanks for taking the time to watch and comment. Yes, you are correct. The hotter spark is blue. I mis-spoke. It's visible to the naked eye, but on camera they look the same. Thanks again for watching. Hope this video solved your problem if you were having these symptoms. It has helped quite a few people.

[@sunnylepone9600]

Great

[@mkdhdinfiniteendlessconten3873]

Thanks for taking the time to watch and comment. Glad you enjoyed it. Hope it was helpful.

[@KANSASIOUX]

That battery connect was falling off. Meanwhile I rebuilt carb! Lol

[@mkdhdinfiniteendlessconten3873]

Hi. Well, now you have a good connection and as a bonus, a rebuilt carb. lol Thanks for watching and commenting.

[@MikeB707]

Appreciate the effort but in all honestly, this method in no way helps anyone trying to learn how to properly diagnose a no start or stalling issue. Basically you had a theory and some luck on your side. At no time did you actually “test” anything. Fixing problems through a process of elimination doesn’t help anyone and can get pretty expensive if you’re just going to throw parts at it. Sorry if I’m being rude but there are way too many “mechanics” out there not knowing proper diagnostic methods.

[@mkdhdinfiniteendlessconten3873]

Well, I was waiting for you to make and upload the video with all the theory of how a coil works and how to check pointlessly check the coil primary and secondary with an ohmmeter which won't reveal a problem as it's a dynamic breakdown under load, show more testing than I already did, and also run fuel pressure checks, maybe even take the top of the carb and watch it run, etc, but looks like I'll have to make that video too since you haven't. lol Not only did I have a theory, I know the theory and teach it as an instructor with Master Mechanic and A&P Credentials with over 50 years of experience. There is no luck involved. When I replace a part, it's faulty. Period. The video exactly accomplishes what the Title and Description say. The point was to "Quickly Diagnose The Sneaky Weak Ignition Coil" which is exactly what the video does. I explained and demonstrated how similar and the subtle differences in fuel starvation and a coil breaking down under load. Knowing and recognizing those differences I didn't waste time on the fuel system. I have clear filters and can watch the fuel flow. I knew to grab the test coil I already have on hand and do a quick jumper of it to Quickly confirm it was indeed the coil breaking down under load which the only test is to swap it and confirm or rule it out. This is not "throwing parts at it". As for testing, I actually do show a spark comparison, but it's hard to see the difference on camera. Anyhow, after solving the problem in minutes, a few days later I thought it would be nice to make a video and help people out, which if you read the comments you'll see that it has. This video has been viewed just under 18K times in a year and from the people that took the time to leave a "Positive" comment and 226 Likes it certainly has solved this issue for those who took the time to comment. I'm sure there's more. So, you've given me a good idea for another video and since I don't want anyone disappointed I'll go ahead and make that video teaching/demonstrating/showing testing and theory. Maybe even give you a shout out. Stay tuned...

[@MikeB707]

I’m sorry if I pissed you off but my comment remains spot on. Having your video watched 18,000 times or 18,000,000 times doesn’t make it good content. It simply means you passed on your hackery to more unsuspecting people and created more hacks. If you’re in fact a “Master” / “instructor”, you should have taken the time to present a useful/ educational video. Now, because I pissed you off, you’re going to make a new video? That’s great. Just remember to delete the first one after you upload the new one. There’s already enough uneducated “back yard mechanics”out there watching unhelpful content such as yours. Let me know when the new video comes out. If it’s good, I’ll be the first to give it a thumbs up. Thanks for sharing your thoughts.@@mkdhdinfiniteendlessconten3873

[@jecrpalier]

But good spark always blue. Bad yellow/orange

[@mkdhdinfiniteendlessconten3873]

Hi. Thanks for watching and taking the time to comment. Yes, I agree on the spark color. I must have been kicked in the head by a mule when I miss spoke on that. I will at some point do a better companion video with a drill driven distributor and good and bad coil to show that better. Fortunately the main point of the video to rule out the fuel system if you have these symptoms has solved the problem for numerous folks. It's a quick check and most folks that tinker have another coil in their stash. Coils can have shorted windings that will check good with an ohmmeter as the resistance range for "good" on both the primary and secondary windings is a wide range. They'll appear fine at idle and low rpms but under real loads and the higher frequency of a higher rpm will break down over 3,000 rpm and their high voltage output will significantly drop. Seems like a fuel starvation problem (which I also have a video for) but is actually the coil. Again, thanks for watching and taking the time to comment.

[@vmunoz90]

Spark may cause battery to explode from gasses causing injury or blindness find a better safer way imo

[@mkdhdinfiniteendlessconten3873]

Technically, yes a remote possibility so I'll give you credit for noting that. Being that it's a healthy battery not drawing current in a charging situation there would be no Hydrogen gas present, at best negligible ppm's with the hood open and a breeze blowing it's not a factor. If that coil's spark couldn't light an atomized compressed fuel mixture in the cylinder it's not going to ignite possible trace hydrogen in free air.

[@johnmiley458]

@@mkdhdinfiniteendlessconten3873 That is exactly right. I've seen many batteries explode. It takes certain conditions. . In fact In Vietnam I got qualified EOD. The conditions for a battery explode weren't there.

[@acecraige6419]

Amazing,,,and,, so ,Borring,😅😅😅😅

[@daydae2213]

It don't look like a bad coil🙄

[@mkdhdinfiniteendlessconten3873]

Hi. Not sure why you would think that, but if I still have it, if you pay the shipping I'll send it you and you can see for yourself. ;-) It will start breaking down around 20 mph before the trans shifts to 2nd.

[@kevinsummers9449]

Thnx brutha

[@mkdhdinfiniteendlessconten3873]

Hi. Thanks for watching and taking the time to comment. Glad the video helped you out.