Coil on plug failed - should I replace all?

S

SC Maintenance

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Jun 8, 2022
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My indestructable Xterra suddenly started running like crap after a about 80 miles of a 100 mile round trip. I nursed it home on less than 6 cylinders, hence it maintains its status as most reliable vehicle ever.

Anyway, P0304, swapped coils between 2 and 4, miss moved to 2 - so bad coil. I had a couple used junk yard ones I grabbed a while back so stuck one on - that seems to have fixed the miss. Changed the plug for good measure since I have a set here - there nearing time again - this plug has about 90K on it - spec is 105K change interval. Doesn't look good either, might have been missing intermittently for a while?

So anyway, should I change all 6 coils now that I have had one fail? I have the plugs, they are already in the to do category. I have a couple other items to do at the same time:

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Worn plugs are hard on the coils. Change all plugs ASAP. Coils, I'd wait till each fails. That's unless downtime is a hardship, then of course you factor what reducing chances of failure is worth vs the time and cost of multiple subsystems you prematurely replace, hoping that's enough.

Since you stated it's another set of plugs and 90K on a 105K interval, presumably putting the vehicle at 195K mi or more, the conservative, it's-not-my-money answer would be sure, replace the coils too, then don't wait till another 90K mi to replace the plugs next time.
 
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How many miles on your Xterra? Maybe keep a spare in the glove box. I imagine a new set could be pricey...
I would put a fresh set of plugs in. You can inspect the coils for cracking, whatever. Probably no reason to swap out the coils.

Good luck!
 
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I should have mentioned all coils have 390K on them. Its my hobby car. So I guess they don't owe me anything. I plan to keep this thing forever. No rust in South Carolina.

The OEM coils are Hanshin - aka Hitachi. Rock Auto sells Hitachi coils for $34, so I guess there now on the to do list? Four I can change in the dark with one hand, one is a bit harder, and one is under the upper intake - but I can change it without removing the intake - I have before. However I need to remove the intake to change a valve cover gasket anyway, so I will get it all done at once sometime this summer.

Thanks for the input!
 
I've been burned twice before on coils that should've been good

If it's not a financial hardship, use all Hitachi coils and the OE NGK/Denso plug, and roll on reliably

If the budget is an issue, put the new coils under the plenum/intake, now you have 3 spares to swap on the accessible bank
 
When you replace the plugs, you will disturb the boots on the coils. They may be fine for a few miles, but the moving of the boots will probably cause problems shortly down the road with coils that have that many miles. Replacing all the coils may be expensive, but not near as costly as having one fail completely on the road. My vote would be to replace all of them now with OEM or OEM equivalent coils.
 
390k? This things a beast and doesn’t owe anyone anything. Since you take 100 mile trips in it on occasion, my personal move would be to swap them all if it’s in the budget, or at least keep a spare in the glovebox with a cheap 10mm ratchet or whatever else might be needed for a quick parking lot repair.
 
Dave9 said:
Worn plugs are hard on the coils. Change all plugs ASAP. Coils, I'd wait till each fails. That's unless downtime is a hardship, then of course you factor what reducing chances of failure is worth vs the time and cost of multiple subsystems you prematurely replace, hoping that's enough.

Since you stated it's another set of plugs and 90K on a 105K interval, presumably putting the vehicle at 195K mi or more, the conservative, it's-not-my-money answer would be sure, replace the coils too, then don't wait till another 90K mi to replace the plugs next time.
Click to expand...
Exactly why I change 100k plus at about half claimed life. Cheaper than coils and car runs better.
 
SC Maintenance said:
My indestructable Xterra suddenly started running like crap after a about 80 miles of a 100 mile round trip. I nursed it home on less than 6 cylinders ... ...

So anyway, should I change all 6 coils now that I have had one fail? I have the plugs, they are already in the to do category. I have a couple other items to do at the same time:

View attachment 161075View attachment 161074
Click to expand...
Keep a spare and tools to change it in the vehicle. I don't like the look of burn and mixture on those plugs. Is your MAF clean, 02 sensor healthy? Gas milage at EPA rating or above?

Are those Denso TT? COP don't require TT, just waste-spark systems with double-ended shared coil. Denso TT fire from GND to Center better than a STD Iridium in the lost spark mechanism.

I would run a set of std NGK or Autolite Ir plugs.
 
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Ask yourself this question - "How will I be inconvenienced if this unknown part fails"? Only you can answer the question, and depending on your POV you most likely will be awarded with the correct answer.
 
Depending on the age, and model you may get a check engine light from replacing just a single coil. The light will obviously not hurt anything but most newer vehicles are capable of measuring the resistance between all coils/plugs, when it notices one with an abnormal resistance it can trigger the check engine light.

While you would have likely mentioned it the possibility is worth considering.
 
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