Help please with ignition coils

"Ignition coil/s failing (highly unlikely and extremely rare on P2 cars with OE coils) but when a coil fails, it always does so under load or when hot!" (LeeT5's post elsewhere.)

Please may my much-loved 2004 S60 2.0T auto ask how coils fail ? Do they stop working completely or just reduce the HT voltage ?

Said S60 has just passed 118000 miles and runs perfectly at all times to my old but experienced ear, but the MPG around the hilly, bendy local area has dropped from average 24 to 22.

I know the weather's cold but the engine always gets fully hot and plenty of load uphill :rally_dri. I don't know if they're OE coils. The car has been serviced regularly by an expert friend who has never billed me for coils.

IIRC the single coils of the "good old days" used to age and need replacement, and I wondered if this applies here.

If so, can anyone please advise the best bang for my bucks ?

Cheers
keith

Yes they do fail , best get a code reader on it to see if you are getting a miss fire code.
Do you know what plugs you are running ?
Also check the engine temperature to make sure you you are at the correct temp.

Quote:

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Originally Posted by MistralS60

"Ignition coil/s failing (highly unlikely and extremely rare on P2 cars with OE coils) but when a coil fails, it always does so under load or when hot!" (LeeT5's post elsewhere.)

Please may my much-loved 2004 S60 2.0T auto ask how coils fail ? Do they stop working completely or just reduce the HT voltage ?

Said S60 has just passed 118000 miles and runs perfectly at all times to my old but experienced ear, but the MPG around the hilly, bendy local area has dropped from average 24 to 22.

I know the weather's cold but the engine always gets fully hot and plenty of load uphill :rally_dri. I don't know if they're OE coils. The car has been serviced regularly by an expert friend who has never billed me for coils.

IIRC the single coils of the "good old days" used to age and need replacement, and I wondered if this applies here.

If so, can anyone please advise the best bang for my bucks ?

Cheers
keith

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The copper coil winding inside the coil breaks / open circuit and you lose the spark. This usually occurs when hot and under load, but can also occur cold.

Thanks very much, Harvey and Lee.

H: I've not been told of a misfire code, and the plugs will be aftermarket (Should be Volvo ?). The temp gauge never exceeds midway (90 degC ?).

L: So once broken it stays broken and there will be a constant misfire ? (Never heard of self-healing copper !)

SWMBO's 2004 S40 1.8 has just had a coil replaced ...

They don't self heal, as you say, but the coil windings which are made of copper do get very hot. Consequently, the copper strands break. On rare occasions. They remake contake, usually when cold and the misfire is gone. Once the engine warms up and the coils get hot, they expand and so you get a misfire again.
This is rare that this happens but I have seen it.

I had that exact problem as described by Lee, but it was with a Citroen ZX 16V I used to own... we solved the issue by placing the misfiring hot coils into a freezer and the misfire was gone, alllowed us to also check which one and sort the issue... bit of a Heath Robinson method but it was years ago (20 to be precise) and info was less readily available on resistance etc