Replacing all coilpacks

Joined
Jun 25, 2009
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Chicago
I've never replaced all coilpacks. Logically i understand the situation.

We can assume all coil packs have roughly same lifespan and should all go out roughly the same amount time. But I've always replaced single coilpacks unless its a rear bank and then I might suggest doing all 3 rears.

However I'm working on a honda fit. No exactly cylinder code, just a P0300 random misfire. It slightly misfires at idle but definitely at 3-5k RPM. Looking at the misfire counts, its primary on 4 and 2 but 1 and 3 still misfire as well. Reading the forums, seem like the motor likes to eat coilpacks at 75k. The car I'm working on is at 100k.

I replaced #4 and while it was the main cause, the other cylinders still misfire slightly. I'm tempted to sell the other 3 coilpacks just to rule out that.
 
Joined
May 25, 2005
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ROCHESTER, NY
IDK the proper procedure for testing the coil packs except for "process of elimination" by moving them around from plug to plug. If you've determined that the cp's are the issue, replace them all. And make sure you use OE!!!!!

Don't rule out other factors that can cause misfires.

Spark plugs are good/gap, oil around the plugs?
Valve cover leaking inside?
PCV?
 
Joined
Oct 17, 2019
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Close to arctic circle
If you plan keeping the car for a long time, replacing all of the coils are a good thing. Combine that with spark plug replacement and you are doing well. After a quick search online it seems like coil packs last about 100k and your car is at that mileage right now, might as well do it.
I did on mine at 110k mileage as i plan to keep the car, i need it as i can`t afford new one.
 
Joined
Oct 9, 2004
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13,089
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Cincinnati, OH, USA
My set of 8 RA Densos just showed up yesterday for the 4.6 2V Grand Marquis in my sig. At 135K, it's overdue-new plugs stopped the code it was throwing, but the butt dyno still feels missing at light acceleration on the highway.
 
Joined
Nov 20, 2006
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MA, Mittelfranken.de
I bought one of these, excellent tool that works perfectly. It can save a lot of money. Well worth owning IMO.
You do not have to remove the coil or disconnect anything just touch the top of the coil with the probe and get a lot of info about its condition good/bad.

 
Joined
Jun 26, 2003
Messages
12,673
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Illinois
If I remember correctly on an '08 Fit I had, you have to remove the intake and part of the cowl to get at the coils. If you're going through all that trouble, replace them all.
I took a similar strategy with my daughter's V6 Escape. One of the rear coil packs was bad. Since she was buying, it was three new coil packs, 6 new plugs and a gasket set as the intake had to come off.

I replaced the rear packs and plugs, and just the plugs in front. Kept the two "good" coil packs as spares if a front one failed. She drove it another two years that way before trading for her 2015 Prius a year ago.

I believe it had over 150k miles when I did the replacement and probably around 170k when she got rid of it, so I wasn't about to suggest she spend a lot of cubic dollars on that rust bucket.
 
Joined
Jul 20, 2020
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77
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Omaha Ne.
Many coils are wired in series with each other, and some fire twice per engine cycle. Called wasted spark, anyhow usually you get get a series of coil failures one after the other. Ford 4.6 and 5.4 is one example.
 
Joined
Nov 3, 2018
Messages
1,273
Location
CA
Probably needs a valve adjustment. Check the MAP sensor voltage at hot idle in park. If it is over .9-.95v, it needs adjustment.
Back in the old days, a vacuum gauge was your friend. Now with the new tech, live data is your friend.
 
Joined
Apr 3, 2017
Messages
3,081
Location
Ontario, Canada
We always recommend all of them. Customers often refuse and only want the bad one replaced, then they are usually coming back every couple of months with another misfire. I always do them all on my own cars.

And as a BMW tech, what’s engine vacuum? LOL
 
Joined
Apr 1, 2019
Messages
699
Location
Pennsylvania
I bought one of these, excellent tool that works perfectly. It can save a lot of money. Well worth owning IMO.
You do not have to remove the coil or disconnect anything just touch the top of the coil with the probe and get a lot of info about its condition good/bad.

Whether the scope on a rope works or not depends alot on the construction of the coil. Pencil coils like on a Honda have the coil windings down inside the spark plug tube which makes it incredibly hard to get a decent signal with the scope on a rope or even a COP pickup and a regular lab scopes. As coil shielding gets better and better it gets harder and harder to gain any info about secondary with an inductive pickup. We usually have to use high tension extension leads between the coil and plug so we have a place for a regular secondary pickup.
 
Joined
Apr 1, 2019
Messages
699
Location
Pennsylvania
I've never replaced all coilpacks. Logically i understand the situation.

We can assume all coil packs have roughly same lifespan and should all go out roughly the same amount time. But I've always replaced single coilpacks unless its a rear bank and then I might suggest doing all 3 rears.

However I'm working on a honda fit. No exactly cylinder code, just a P0300 random misfire. It slightly misfires at idle but definitely at 3-5k RPM. Looking at the misfire counts, its primary on 4 and 2 but 1 and 3 still misfire as well. Reading the forums, seem like the motor likes to eat coilpacks at 75k. The car I'm working on is at 100k.

I replaced #4 and while it was the main cause, the other cylinders still misfire slightly. I'm tempted to sell the other 3 coilpacks just to rule oI

I would start by actually testing to get to the bottom of the misfire rather than playing swaptronics with the customers money
 
Joined
Feb 20, 2007
Messages
6,579
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Southeast
I had misfires years ago in a 2.2L ‘ru. It was from a timing belt which stretched enough to cause a random burp at idle. Nobody could figure it out, it was by chance that I replaced the tb early when the water pump failed and the misfire went away.
 
Joined
Nov 20, 2006
Messages
29,177
Location
MA, Mittelfranken.de
Whether the scope on a rope works or not depends alot on the construction of the coil. Pencil coils like on a Honda have the coil windings down inside the spark plug tube which makes it incredibly hard to get a decent signal with the scope on a rope or even a COP pickup and a regular lab scopes. As coil shielding gets better and better it gets harder and harder to gain any info about secondary with an inductive pickup. We usually have to use high tension extension leads between the coil and plug so we have a place for a regular secondary pickup.
I tried it on a 2020 Honda 1.5 and it worked fine but I can see where it could be a problem. Just another tool that may not work on everything like so many others. As you say when it doesn't you find something that will.
 
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