We have had three out of four coils go in our 2000 Nissan Sentra. We know this is an unusual problem and so we think something else is causing the coils to flip their lids. Any ideas as to what the underlying cause could be?
By the way, the check engine light always says “Swirl Valve” - but nothing’s wrong with that. While I don’t think they’re related, maybe you know better than me.
If the swirl valve problem has been checked and verified as trouble free (why does the CEL keep saying otherwise?) then I would ask how many miles on the car and how long are the spark plugs allowed to remain in the engine without being replaced?
Aged spark plugs can kill ignition coils over time.
I’m not sure why the swirl valve keeps coding… wish I knew because it makes it difficult to register the car every year. They’ve checked the swirl valve two years in a row and found nothing wrong (but that doesn’t keep the code from coming back, even within 30 miles).
The car has 145,000 miles and the spark plugs haven’t been changed since I got it (5 years ago)… so that sounds like a good fit (in all my infinite wisdom). If they say that than I’ll feel safe in making a repair.
Thank you.
About how much should it cost to replace spark plugs?
Replacing the plugs should not be much at all. I prefer Autolite, Bosch, or NGK plugs and generally use the regular copper core plugs which are inexpensive. Platinum plugs are more costly but last a bit longer on average. Try to stick with what Nissan recommends for your car and you won’t go wrong.
Labor varies so that’s hard to say. The east and west coasts are higher usually. Here in the mid-section of the country one could probably figure on 40 bucks or so labor and plugs will probably be in the 10-20 dollar range depending on the plug type used.
JMHO here, but whenever coils are replaced the plugs should also be replaced at the same time unless it is known for a fact the plugs were just recently changed. With the coils removed one is already 95% of the way there anyway so spend a few more minutes and kill two birds with one stone. Hope that helps. 
(And the plug gap should always be double checked before installation. It should never be blindly assumed the gap on the plugs is correct for the application.)