Blown coil on 99 Grand Marquis LS.

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Starscream - 30 Sep 2006 02:38 GMT

the Coil on cylinder #2 died on me last week. Replaced it (along with
the plug), (well, got it replaced since I don't have the OBD2 reader to
reset the codes afterwards). is it normal for those things to die after
52,000 miles? SInce I've got 8 of these, I'm worried it could get
expensive pretty fast :)

Am I right in assuming I could've saved some money by just unplugging
the battery, or do OBD2 computers need a software reset too?

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Tom - 30 Sep 2006 10:55 GMT

sometimes they just go. my crown vic had a coil die with 32,000 miles on it.
the 97 grand marquis has 145,000 miles on it, and all 8m original coils.

> the Coil on cylinder #2 died on me last week. Replaced it (along with the
> plug), (well, got it replaced since I don't have the OBD2 reader to reset
[quoted text clipped - 4 lines]
> Am I right in assuming I could've saved some money by just unplugging the
> battery, or do OBD2 computers need a software reset too?

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Tom Adkins - 30 Sep 2006 12:46 GMT

> the Coil on cylinder #2 died on me last week. Replaced it (along with
> the plug), (well, got it replaced since I don't have the OBD2 reader to
[quoted text clipped - 4 lines]
> Am I right in assuming I could've saved some money by just unplugging
> the battery, or do OBD2 computers need a software reset too?

The coils themselves do fail occasionally, but the most common failure is the spark
plug boot. The boot is a servicable part and should be changed at ~80K miles or so
just like spark p;ug wires.

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Starscream - 01 Oct 2006 01:26 GMT

>> the Coil on cylinder #2 died on me last week. Replaced it (along with
>> the plug), (well, got it replaced since I don't have the OBD2 reader
[quoted text clipped - 8 lines]
> is the spark plug boot. The boot is a servicable part and should be
> changed at ~80K miles or so just like spark p;ug wires.

???

I still have the blown part, and it doesn't seem to be serviceable.

Do you mean I can take the rubber part and its connector (the big
spring) from the coil and just replace those?

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Tom Adkins - 01 Oct 2006 03:22 GMT

>>> the Coil on cylinder #2 died on me last week. Replaced it (along with
>>> the plug), (well, got it replaced since I don't have the OBD2 reader
[quoted text clipped - 15 lines]
> Do you mean I can take the rubber part and its connector (the big
> spring) from the coil and just replace those?

Just the rubber part. The spring will pull off too but I don't believe it's
available as a separate part. Grab the coil in one hand, the boot in the other near
the coil, twist and pull.
Look closely at the rubber around the plug opening. If it's bad, there will likely
be a carbon track (uneven grey\black color). If not there look at the side of the
boot. You may see a tiny burnt spot with a grey corona where the spark was leaking
through to the cylinder head. If there are signs of liquid (oil\coolant) on the boot,
the moisture contaminated the spark plug well and caused the spark to bypass the plug.
If you know how to use an ohm meter, you can check the windings in the old coil.
Check across the connector terminals, then from the spring contact to the metal insert
in the screw hole. I don't recall the spec, but they should both show continuity.
The coil could very well be bad, but I've seen the boots fail WAY more often.

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Starscream - 03 Oct 2006 01:17 GMT

>>>> the Coil on cylinder #2 died on me last week. Replaced it (along
>>>> with the plug), (well, got it replaced since I don't have the OBD2
[quoted text clipped - 31 lines]
> The coil could very well be bad, but I've seen the boots fail WAY more
> often.

I didn't have my DBM with me (coil is at work), but I couldn't see any
traces of either contaminants, carbon track, so on...

I'll try to think about bringing my DVM to work (or the coil at home :)

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ShoeSalesman - 30 Sep 2006 19:27 GMT

yes, its ok to just disconnect the battery for a few minutes to clear
the code.

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Starscream - 01 Oct 2006 01:28 GMT

>> the Coil on cylinder #2 died on me last week. Replaced it (along with
>> the plug), (well, got it replaced since I don't have the OBD2 reader
[quoted text clipped - 7 lines]
> yes, its ok to just disconnect the battery for a few minutes to clear
> the code.

Thanks all of you...

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C. E. White - 02 Oct 2006 15:16 GMT

> the Coil on cylinder #2 died on me last week. Replaced it (along with the
> plug), (well, got it replaced since I don't have the OBD2 reader to reset
> the codes afterwards). is it normal for those things to die after 52,000
> miles? SInce I've got 8 of these, I'm worried it could get expensive
> pretty fast :)

I've had several vehicles with these coils and only replaced one (most miles
on anyone vehicle was 147,000). There is better than a 50/50 chance that the
actual coil was OK, and just the plug boot was bad (or the plug itself). The
plug boot is the short connecting wire between the coil and the plug. They
fail at least as often as the coils and when they fail it is difficult to
tell that failure from a coil failure. Ford has an elaborate diagnostic
procedure for this, but the amount of labor need to complete the diagnosis
is greater than the cost of just replacing the coil, boot, and plug.
Therefore most shops just replace all three anytime a miss-fire for a
particular cylinder is indicated. I always recommend replacing the plug
boots whenever you replace the plugs. They are cheap compared to replacing
even one coil, boot, and plug combination.

> Am I right in assuming I could've saved some money by just unplugging the
> battery, or do OBD2 computers need a software reset too?

Just disconnecting the battery would have reset the light, but then just
waiting for a few days would have reset it as well. Once the problem was
fixed, the code would have eventually cleared when the PCM could no longer
detect the misfire.

Ed

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