Coil packs how long do they last?

[blue62]

Originally Posted by Boxstard

I thought the coil either works or doesn’t and when it doesn’t CEL gets triggered and you know it from the code. I got a 97 with 98K miles, with what appear to be original coils. One tube had split but just used electric tape for insulation. I don’t mind replacing them if aged coils affect engine performance appreciably but I’m not convinced if this is true,

I had a 2003 Saab for 16 years and put 170K miles on it, and its coil cartridge is considered a wear item, replaced it every 30K miles or so and carried a spare in trunk just in case. It went through several design revisions too so apparently some design flaws involved. You still gets CEL and code to know it’s gone.

So it’s case by case but it seems coils on 986 are designed well and robust.

Your assumptions are incorrect
Ignition coils can fail totally or they can exhibit intermittent failure.
They can also exhibit weak spark and never miss or fail.

Also there is no CEL (OBDII) code for ignition coils.
There are codes for misfires, but misfires can be caused by many factors not just coil issues.

[986 Boxster]

Originally Posted by blue62

Your assumptions are incorrect
Ignition coils can fail totally or they can exhibit intermittent failure.
They can also exhibit weak spark and never miss or fail.

Also there is no CEL (OBDII) code for ignition coils.
There are codes for misfires, but misfires can be caused by many factors not just coil issues.

Yes you're right, you don't get a code for a coil being bad, but you do get a code for a miss fire, and 99% of the time it's a bad plug or a bad coil. So it's very simple to figure out if you have a bad coil or a bad plug. Let's say you get a code for cylinder #4 for example, all you have to do is change a coil from a different cylinder to #4 and you will know if you have a bad coil or a bad plug. If the code comes back to cylinder #4 you know you have a bad plug, but if the code comes back to the cylinder that you changed the coil to, you know it's a bad coil

[blue62]

Originally Posted by 986 Boxster

Yes you're right, you don't get a code for a coil being bad, but you do get a code for a miss fire, and 99% of the time it's a bad plug or a bad coil. So it's very simple to figure out if you have a bad coil or a bad plug. Let's say you get a code for cylinder #4 for example, all you have to do is change a coil from a different cylinder to #4 and you will know if you have a bad coil or a bad plug. If the code comes back to cylinder #4 you know you have a bad plug, but if the code comes back to the cylinder that you changed the coil to, you know it's a bad coil

All true if you have a bad plug or bad coil.
You could also have a coil wiring issue on cylinder #4
You could also have a fuel injector issue or injector wiring issue on cylinder #4
Or valve train issues on cylinder #4 ect.ect.ect.
And get the same #4 cylinder misfire code.

My point to the OP was there is no CEL or OBDII codes that tell you a coil is faulty.

Misfire codes are triggered for many reasons depending on frequency and severity of the misfire.
The reason for the misfire as you pointed out has to be determined by diagnostics.

[Boxstard]

Originally Posted by blue62

All true if you have a bad plug or bad coil.
You could also have a coil wiring issue on cylinder #4
You could also have a fuel injector issue or injector wiring issue on cylinder #4
Or valve train issues on cylinder #4 ect.ect.ect.
And get the same #4 cylinder misfire code.

My point to the OP was there is no CEL or OBDII codes that tell you a coil is faulty.

Misfire codes are triggered for many reasons depending on frequency and severity of the misfire.
The reason for the misfire as you pointed out has to be determined by diagnostics.

OK I stand corrected but coil failure is still easily diagnosed with the CEL code for misfiring. Intermittent failure/ misfiring can be felt, if it does not trigger CEL. Ilm still skeptical if ‘weak’ spark from an aged coil can appreciably reduce engine power, and if so what characteristics one can check on a coil and justify replacement.

[blue62]

Originally Posted by Boxstard

OK I stand corrected but coil failure is still easily diagnosed with the CEL code for misfiring. Intermittent failure/ misfiring can be felt, if it does not trigger CEL. Ilm still skeptical if ‘weak’ spark from an aged coil can appreciably reduce engine power, and if so what characteristics one can check on a coil and justify replacement.

Start with a visual inspection.
I always use a flashlight.
If they have any type of physical damage like cracks in the housing (even hairline cracks) I replace them.

A simple test you can do on a coil yourself is an Ohm's resistance test.
If a coil doesn't meet manufactures spec. it should be replaced.
You can usually find the manufactures spec on the internet.
All you need for the test is a Digital multi meter.
If you do your own auto work you should have a Digital multi meter in your tool box.

[DrRobin]

Thanks everyone, that is quite a spread of miles out of a set of coils and it looks like mine are typical.

When the dealer changed mine from original to Beru 10 years and 40k miles ago I did notice a difference, the engine ran smoother. There was no misfire or CEL.

When I have just changed them now, all six had at least one small crack, but the difference isn't quite as noticeable, it is running a lot better, but was after stripping out one side and cleaning the coils/plugs. I did test the coils with a meter, the values for resistance were within spec.

I did get a CEL a couple of months ago, but that was when the battery was quite weak, so in my experience to answer a couple of questions posed here:

- If you have a weak spark, you might not get a misfire or CEL, but you will get poor burning of the fuel and it will lead to rough/poor running.

- Cleaning all the crud off the coils and the plugs will always help.

- If the coil has cracks in it then it will start to break down, especially when wet and this will produce a weak spark/CEL.

- I got Beru coils in the UK for £31 each, at that price it isn't worth fitting anything else. I also got 6 Denso original fitment spark plugs for about £28, again not worth cleaning the old ones which looked fine to me.

So for about £210 (and a couple of afternoons) I have new coils, new plugs, the old plugs didn't show anything out of the ordinary so I am happy that my 986 at 93k miles is good for another few miles.

[Boxstard]

Originally Posted by blue62

Start with a visual inspection.
I always use a flashlight.
If they have any type of physical damage like cracks in the housing (even hairline cracks) I replace them.

A simple test you can do on a coil yourself is an Ohm's resistance test.
If a coil doesn't meet manufactures spec. it should be replaced.
You can usually find the manufactures spec on the internet.
All you need for the test is a Digital multi meter.
If you do your own auto work you should have a Digital multi meter in your tool box.

Yeah that’s pretty basic…. For me cracking can be repaired and may not warrant automatic replacement, if you catch it early. Body crack can be filled with epoxy, and tube can be insulated with electric tape. One of mine had tube split and taping it up works fine.

I do have a multimeter, but just wondering how to tell actual degradation, instead of just continuity of the coil. Variation in reading within the spec. may come from manufacturing tolerance, instead of aging. If the coils with resistance within the spec. can still produce weak spark, then the check is not effective and I wonder what else can be checked.

[DrRobin]

Originally Posted by Boxstard

Yeah that’s pretty basic…. For me cracking can be repaired and may not warrant automatic replacement, if you catch it early. Body crack can be filled with epoxy, and tube can be insulated with electric tape. One of mine had tube split and taping it up works fine.

I do have a multimeter, but just wondering how to tell actual degradation, instead of just continuity of the coil. Variation in reading within the spec. may come from manufacturing tolerance, instead of aging. If the coils with resistance within the spec. can still produce weak spark, then the check is not effective and I wonder what else can be checked.

When you measure the resistance to be less than 0.7 ohms, that is just the primary coil and my guess would be that it is the secondary which is more important. You can measure the secondary resistance, but a better measurement would be the insultation resistance, for which I haven't seen any figures.

If the insulation has cracked, unless you get all of the moisture out before it is sealed with epoxy you will still compromise the insulation resistance and therefore might end up with a weak spark. I would only do this as a short term fix until new coils can be obtained.

It took me 3 hours to change all six coils/plugs and coils were £31 each in the UK, I doubt it is really worth the effort of removing a coil, drying it out, filling with epoxy and re-fitting, well not in our current autumn climate of cold temperatures and rain.

If you were a little closer, you could have 6 Beru coils, all with at least one crack, but the postage would be more than they are worth.

PS anyone in the UK is welcome to them if they pay the cost of posting from Northumberland.

[blue62]

Originally Posted by Boxstard

Yeah that’s pretty basic…. For me cracking can be repaired and may not warrant automatic replacement, if you catch it early. Body crack can be filled with epoxy, and tube can be insulated with electric tape. One of mine had tube split and taping it up works fine.

I do have a multimeter, but just wondering how to tell actual degradation, instead of just continuity of the coil. Variation in reading within the spec. may come from manufacturing tolerance, instead of aging. If the coils with resistance within the spec. can still produce weak spark, then the check is not effective and I wonder what else can be checked.

Continuity and Ohm's resistance are not the same thing.
They are two different tests.
If you have a variation in reading "within the spec." your still within spec.
Any spec. has an allowable tolerance.
Primary and secondary Ohm's resistance can be checked with a Multimeter.
Spark color can be checked with a simple spark checker.
You want a fat blue spark not a weak yellow spark.
You can do a cylinder power balance test to see if a coil is possibly having a negative power balance effect on the engine.
You can have the coils scoped.

But in my opinion at less then $50.00 apiece shipped to my front door. If I have doubts about the condition of a coil I replace them.
Anything else is penny wise and pound foolish.