# Bad ignition coil **URL:** \ **Category:** Miscellaneous and Personal Stuff I Must Share\ **Created:** [September 29, 2020, 5:52pm UTC](https://boards.straightdope.com/t/bad-ignition-coil/921823 "2020-09-29T17:52:59Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![Cardigan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cardigan/32/187_2.png) [@Cardigan](https://boards.straightdope.com/u/Cardigan)\ **Post date:** [September 29, 2020, 5:52pm UTC](https://boards.straightdope.com/t/bad-ignition-coil/921823/1 "2020-09-29T17:52:59Z")
My car started running rough a couple of days ago. My mechanic friend stopped by and hooked his little diagnostic gizmo up. The error code said the ignition coil is going bad on my #2 cylinder. The good news is that’s a relatively inexpensive fix. If I knew what I was doing I’d replace it myself, but as it happens I don’t. My question is - would it be likely to damage the car if I continued to drive it the 2.5 miles between work and home for a couple more days without replacing it? ---
**Author:** ![74westy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/74westy/32/3950_2.png) [@74westy](https://boards.straightdope.com/u/74westy)\ **Post date:** [September 29, 2020, 5:57pm UTC](https://boards.straightdope.com/t/bad-ignition-coil/921823/2 "2020-09-29T17:57:25Z")
If that cylinder is missing, it will allow raw gas into the catalytic converter and wreck it. Is the check engine light flashing? If it is, driving could cause harm. ---
**Author:** ![Cardigan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cardigan/32/187_2.png) [@Cardigan](https://boards.straightdope.com/u/Cardigan)\ **Post date:** [September 29, 2020, 5:58pm UTC](https://boards.straightdope.com/t/bad-ignition-coil/921823/3 "2020-09-29T17:58:34Z")
It did flash on briefly. Doesn’t sound like driving it is worth the risk ---
**Author:** ![74westy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/74westy/32/3950_2.png) [@74westy](https://boards.straightdope.com/u/74westy)\ **Post date:** [September 29, 2020, 6:00pm UTC](https://boards.straightdope.com/t/bad-ignition-coil/921823/4 "2020-09-29T18:00:47Z")
If it’s not flashing on and off you should be ok but listen to the more knowledgeable posters who will be here soon. ---
**Author:** ![kayaker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kayaker/32/441_2.png) [@kayaker](https://boards.straightdope.com/u/kayaker)\ **Post date:** [September 30, 2020, 2:30pm UTC](https://boards.straightdope.com/t/bad-ignition-coil/921823/5 "2020-09-30T14:30:03Z")
> [@Cardigan](#): > > If I knew what I was doing I’d replace it myself, but as it happens I don’t. Your friend did the hard part by diagnosing the problem. [Check out this video, it’s super simple…](https://www.youtube.com/watch?v=5aVDcufzrBw) ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [September 30, 2020, 2:48pm UTC](https://boards.straightdope.com/t/bad-ignition-coil/921823/6 "2020-09-30T14:48:20Z")
> [@74westy](#): > > If it’s not flashing on and off you should be ok but listen to the more knowledgeable posters who will be here soon. It’s important to emphasize the difference between a check-engine light (sometimes called a “MIL”, = Malfunction Indicator light) that is flashing and one that is just steady on (without flashing). If the MIL comes on and stays on, you’ve got a problem that needs fixing, but you can continue to drive your car without worrying too much about it (though if your state has an emissions inspection, you’ll fail it). If the MIL is flashing, you’ve got a problem that may cause expensive damage if you continue to drive. In the present case, yes, ongoing misfire can dump unburned mixture into the exhaust stream; the cat can oxidize it, causing it to overtemp the catalytic converter. Worst case is a fire, but slightly less bad is the sintering of the catalytic material, reducing conversion efficiency; if that happens, you may fail an emissions check even after you fix the misfire problem - in which case you’ll need to buy a new cat, and those ain’t cheap. ---
**Author:** ![bump](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@bump](https://boards.straightdope.com/u/bump)\ **Post date:** [September 30, 2020, 4:36pm UTC](https://boards.straightdope.com/t/bad-ignition-coil/921823/7 "2020-09-30T16:36:11Z")
If it’s like my truck is, each cylinder has its own little ignition coil that sits on top of the spark plug. Replacing it would be pretty easy, I suspect, as the coils themselves just bolt to the head, and have a connector to the electrical system. To change the plugs, you have to remove the coils anyway. The biggest part will be figuring out which cylinder it is, if your OBD stuff doesn’t tell you. ---
**Author:** ![Dallas\_Jones](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dallas_jones/32/3277_2.png) [@Dallas\_Jones](https://boards.straightdope.com/u/Dallas_Jones)\ **Post date:** [September 30, 2020, 5:39pm UTC](https://boards.straightdope.com/t/bad-ignition-coil/921823/8 "2020-09-30T17:39:38Z")
What type/brand/model of vehicle are we talking about? Pretty simple fix if you know someone with a modicum of mechanical knowledge. Of course the vehicle likely has plastic engine covers that will intimidate most people from doing that. ---
**Author:** ![gotpasswords](https://avatars.discourse-cdn.com/v4/letter/g/c57346/32.png) [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)\ **Post date:** [September 30, 2020, 5:41pm UTC](https://boards.straightdope.com/t/bad-ignition-coil/921823/9 "2020-09-30T17:41:08Z")
It’s already known to be #2. The question becomes “Which one is #2?” On a 4-cylinder, it’ll be the second one away from the belt(s). On a 6, it should be the first one on the left, just behind the belt(s). ---
**Author:** ![K2500](https://avatars.discourse-cdn.com/v4/letter/k/f6c823/32.png) [@K2500](https://boards.straightdope.com/u/K2500)\ **Post date:** [September 30, 2020, 8:17pm UTC](https://boards.straightdope.com/t/bad-ignition-coil/921823/10 "2020-09-30T20:17:20Z")
Your left or the engines left? ---
**Author:** ![gotpasswords](https://avatars.discourse-cdn.com/v4/letter/g/c57346/32.png) [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)\ **Post date:** [October 1, 2020, 4:45pm UTC](https://boards.straightdope.com/t/bad-ignition-coil/921823/11 "2020-10-01T16:45:19Z")
Your left, as you look at the end with the belts. ---
**Author:** ![kayaker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kayaker/32/441_2.png) [@kayaker](https://boards.straightdope.com/u/kayaker)\ **Post date:** [October 2, 2020, 11:05am UTC](https://boards.straightdope.com/t/bad-ignition-coil/921823/12 "2020-10-02T11:05:54Z")
AKA passenger side ---
**Author:** ![QuickSilver](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/quicksilver/32/7832_2.png) [@QuickSilver](https://boards.straightdope.com/u/QuickSilver)\ **Post date:** [October 2, 2020, 12:08pm UTC](https://boards.straightdope.com/t/bad-ignition-coil/921823/13 "2020-10-02T12:08:23Z")
US or UK? ---
**Author:** ![kayaker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kayaker/32/441_2.png) [@kayaker](https://boards.straightdope.com/u/kayaker)\ **Post date:** [October 2, 2020, 12:09pm UTC](https://boards.straightdope.com/t/bad-ignition-coil/921823/14 "2020-10-02T12:09:01Z")
Argh!!! You got me there. ---
**Author:** ![california\_jobcase](https://avatars.discourse-cdn.com/v4/letter/c/9d8465/32.png) [@california\_jobcase](https://boards.straightdope.com/u/california_jobcase)\ **Post date:** [October 3, 2020, 1:48am UTC](https://boards.straightdope.com/t/bad-ignition-coil/921823/15 "2020-10-03T01:48:44Z")
More likely dashboard side if it’s front wheel drive. ---
**Author:** ![SmartAleq](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/smartaleq/32/163_2.png) [@SmartAleq](https://boards.straightdope.com/u/SmartAleq)\ **Post date:** [October 3, 2020, 5:43pm UTC](https://boards.straightdope.com/t/bad-ignition-coil/921823/16 "2020-10-03T17:43:55Z")
I realize I’m a weirdo, but when it comes to things like ignition coils (and plugs, and plug wires, and most things that come in pairs or multiples on cars) I prefer, if one goes to shit, to replace the lot. As has been pointed out, they aren’t terribly expensive (says the woman with a four cylinder engined vehicle that uses one coil for two cylinders) and my thought is that if one is going, can the rest be far behind? Besides, if I do them all at once (and yeah, absent any recent replacements I’d do the plugs and plug wires at the same time) if just one goes titsy, especially if it makes a habit of it, that’s a big tipoff something bigger is going on and replacing the entire batch is a really good troubleshooting measure. Can you tell I drive old cars that have probably had dodgy maintenance before I got them? 😉