When to replace Ignition coils.

[87warrior]

When I bought my '99 it had 246k miles on it and was running with a very slight hesitation, but no CEL. With the engine cover off I noticed coil #1 had a big Duralast "D" sticker right on top, so I replaced it with a Denso coil. It ran butter smooth again. The other 7 coils looked to be original.

At 268k miles I was on I70 in western Kansas headed home from Colorado (for the 4th time in a year) and would occasionally hear a thunk noise which I attributed to a suspension bushing that needed replacing. The next day I drove it to work without issue until I took it out for lunch. It ran very rough and the CEL started flashing, I pulled P0303 with the Torque app. Replaced coil #3 with a Denso and it is back to smooth.... and that thunk noise I was hearing hasn't returned in 2 months. I suspect the noise was the start of the coil failure by way of a miss.

I now carry a spare Denso coil in the small cubby in the back

 

[2001LC]

I'm always curious of spark plug condition of these failed coils. It's seem very few are even checking.

 

[Wellcraft19]

Goodies arrived yesterday - and yes, will do plugs as well here today. I am just as curious as 2001LC to see what (if any) difference there is in condition on the plug. They are due to be replaced anyway.

 

[Wellcraft19]

New and old spark plug. Both carried about the same electrode gap, about 1.0 mm, so I left it at that (should really be 1.1 mm). Really not much visibly used (even after cleaning it up).
Did only do one plug yesterday as I was running out of time, and will replace all the other ones when the weather has gotten a bit warmer and I can do this and enjoying it.
Funny thing though, is that the 2004 FSM indicates "Spark plug should be replaced every 100,000 km (60,000 miles)" while everywhere else I've could find mention 120,000 miles.

 

[2001LC]

New and old spark plug. Both carried about the same electrode gap, about 1.0 mm, so I left it at that (should really be 1.1 mm). Really not much visibly used (even after cleaning it up).
Did only do one plug yesterday as I was running out of time, and will replace all the other ones when the weather has gotten a bit warmer and I can do this and enjoying it.
Funny thing though, is that the 2004 FSM indicates "Spark plug should be replaced every 100,000 km (60,000 miles)" while everywhere else I've could find mention 120,000 miles.

View attachment 1392443

You'll also see in other spots Toyota/Lexus recommending 60K miles on the spark plugs. It has to do with pollution control requirements. Bottom line is inspection for leaks, resistance and gap all within spec. But since a set cost is much as one coil, changing all plugs as soon as one gap starts to change is good PM.

 

[steelynorm]

2000 lc 239k about to embark on long road trip. Grab son from college.

I pick up locally.
Maf cleaner 8 plugs, a case of 5w-30, new air, oil and drain plug gasket.


No major issues..
With pm.
However I looked at my coils I would say half have hairline fractures in them.
Sorry no pics....my bad.
No cel ..... yet

Probably will pick up One density to have as a backup
I wish I could just buy a full set of densos without having to take a second out.

 

[oakback]

With me at all times is a OBD scanner, a spare coil, and a basic socket set. Once it misfires hard enough to get a code indicating which cylinder (or when it fails completely), I'll replace it wherever I am. This worked for me in the past.

When I replace one I'll buy another spare to keep on board.

 

[RootMeanSqr]

I used to do the exact same thing, until I had replaced 3 on the side of the road within a period of 10-15k miles. At that point, I sucked it up and replaced the rest of them in the comfort of my garage. But I still carry a spare, one of the ones I had taken out.

 

[AZRed]

I replaced my spark plugs the other day, they all appeared normal but I have two ignition coils with slight discoloration. Is this a sign they will fail soon in the future. Engine runs fine, no rough idle though on a side note I am try to diagnose a low MPG issue. Wondering if two bad ignition oils could cause low MPG but if they were bad I would be experience error codes and rough idle which I am not. Below pick is one of the discolored ignition coils next to a normal looking one. Any help on either issue is appreciated.

 

[Julian Stead]

The one on the left looks new, the one on the right looks like it has been in a while. Who knows how long they will last, look at your fuel trims to see if anything is wrong for mpg.

 

[2001LC]

I replaced my spark plugs the other day, they all appeared normal but I have two ignition coils with slight discoloration. Is this a sign they will fail soon in the future. Engine runs fine, no rough idle though on a side note I am try to diagnose a low MPG issue. Wondering if two bad ignition oils could cause low MPG but if they were bad I would be experience error codes and rough idle which I am not. Below pick is one of the discolored ignition coils next to a normal looking one. Any help on either issue is appreciated.


View attachment 1569519

This is a very subjective thing when looking at signs of heat on coils. Yes heat is the enemy/killer of coils, but no one can say how long that one will last. I've looked at some coils that failed and most show signs of heat like that. But I did not see them before failure. The test shown in OP would give better idea, but good luck finding someone with scope/equipment like that.

It will be an excellent experiment if you leave in it and it fails soon (10K to 20K). Anecdotal evidence like that is what will enriches this thread. But now with new plugs at proper gap, coil should cool down a bit and less likely to fail.

As for MPG, I'd first look to vacuum lines, throttle body cleaning and disconnecting battery for twenty minutes while MAF cleaned. You've now got new spark plugs which should help MPG and protect coils. Also newest revelation is over filling oil in crank case, seem this can knock MPG down 30%. Check and try running a tad below high line of dip stick if above. Also tire size, weight and pressure will have it's effect. Along with any electrical device(s) running, like cabin fan running.

Fuel injectors & fuel pressure regulator can have their effects on MPG. A can of 44K can in gas tank can help, but servicing these is only sure way to know.
When to replace fuel injectors

 

[hifu]

209,000 no faults yet

 

[apdxyk]

In 2UZ-FE?

Never. Simply change all the boots when you do your spark plugs. This will save you some money and a lot of frustration.

 

[2001LC]

In 2UZ-FE?

Never. Simply change all the boots when you do your spark plugs. This will save you some money and a lot of frustration.

?

 

[Efjayforty]

I have replaced 6 of them on my 98 but only on two cylinders. I had one go out and replaced it with a new coil from O'reilly's auto. It went out after a year or so and I replaced it under warranty that time and one more time. I had another go out and bought a replacement from Advance Auto. It blew also and I replaced it under warranty one time. One of them blew AGAIN and I bought a used denso off ebay for $20 and it has been running ever since. I travel with a spare (another ebay $20 purchase) ready to go. I have owned the truck for 11 years and when my kids were little, I would let the car run with the AC on sitting in a parking lot or wherever when it was really hot outside and they were asleep or whatever. It took me a few times to come to realize that the sitting and not moving when the temps were high was the one thing that was in common with them blowing. It was never that day but maybe a couple of days or a week later and then one would blow.

 

[2001LC]

In 2UZ-FE?

Never. Simply change all the boots when you do your spark plugs. This will save you some money and a lot of frustration.

@apdxyk I'm unclean on what you mean "boots". Are you saying change all the boots that fit at bottom of coil over spark plugs?

Or are you calling coils "boots" and saying replace all coils (very pricey) at same time as spark plugs?

 

[Rolocado]

211k and put er back in

 

[white_lx]

Just replaced the spark plugs on '00 LX470 with 81k miles (02/00 build date). As far as I know, these have never been touched.

Pretty disappointing to find out that coils 1, 3, 5 and 7 were all cracked. Coils 2, 4, 6 and 8 are fine. Other than the cracks the coils look pristine. No CEL and engine is running great. Seems like a bad batch of coils for the worker on the driver side of the engine.

Spark plugs looked pretty good too with gaps between 1.10mm and 1.15mm. Replaced plugs, but re-installed coils for now.

 

[2001LC]

Interesting all on the easiest side to access. Possibly someone switched coils at some point.

Having one maybe two bad, but four and no indication of high heat .......strange.

 

[white_lx]

Interesting all on the easiest side to access. Possibly someone switched coils at some point.
Having one maybe two bad, but four and no indication of high heat .......strange.

I am pretty sure these were never changed. I've owned this vehicle since 2005. When I purchased it, it had about 50k miles. No real maintenance up to that point other then oil changes. It is remarkable that most coils seem to fail over 200k miles, but that post #2 in this thread is also 2000 LX470 with two failed coils at 67k miles.

A quick search shows this seems to happen on all kind of Toyota's, including 4Runner and Tundra.