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I'm getting to the end of my tether with this one! Some of you may remember me posting various times about a misfire over the last couple of months, which was first cured by replacing two HT leads, but shortly followed by coil pack failure. That was cured by installing an original second hand one, but that gave up the ghost after less than a month so I quickly bought a cheap new replacement, which again worked fine at first, but within 24 hours I got two misfires going around a roundabout. It went quiet for a bit, I checked that the leads and plugs were all secure. But now it's back with a vengeance and I fear a meetup with the man from the AA before I get the problem sorted this week. So what I need to know is a) if there is likely to be an underlying cause for the failures? b) have I just been unlucky with firstly a second hand coil pack that was on it's last legs, and secondly a cheap new one that's not up to the job or c) should I have replaced the plugs and leads when installing the new coil pack (ie. did the previous failed packs harm them, and now in turn they're harming the replacements?) Haha as you may be able to tell I'm only acquainted with the basics on how these things work, so any help appreciated!
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buy plugs & leads from Ford including the coil pack. Fit it all at once. Don't waste time on maoney on sechondhand & pattern parts. If the plugs are the wrong resistance value it plays havoc with the coil packs!
I Doc
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Just to second I Doc's comments on pattern Ford coil packs, my mum had no end of trouble with a misfire on her Ford StreetKa. Indie fitted a pattern coil pack (quite openly) which cured the problem...for two weeks. Ford dealer ended up taking a look, replaced the coil pack again for a genuine Ford one, and it's cured the problem. Shame the misfire had destroyed the cat in the meantime though.
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But why do these coil packs fail?, any body know, is there a pattern , is it age related or distance covered. Seems like a 'black art' finding problems suchas these- very expenive way to do it too.
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It seems as if there is not enough of a safety margin designed into these coils to cope with normal usage. This makes the correct setting of the plug gaps far more critical than it used to be with the traditional pre-electronic design of coil - remember those big fat things that never went wrong?! The wider the plug gaps, the higher the voltage needed to make them spark, putting extra strain on the coil's insulation which is evidently pretty marginal anyway.
Plug gaps inevitably increase with mileage as the electrodes gradually burn away, so even if set correctly (1 mm) when new, you will eventually reach a stage where increased voltages significantly above the coil's design value are called for. So if the plugs have done over 20k miles without being looked at, I would advise that you should at least check the gaps and re-set to, say, 0.9 mm, and this may preserve the coil for you.
I had the original coil fail with a bad misfire on one cylinder on my Ka (52 reg, Duratec) at about 35k miles. You could hear the splats as the coil sparked internally. The plug gaps were about 1.1 mm, which means an extra 10% sparking voltage was needed - evidently enough to find the weak point inside the coil! With new NGK plugs carefully gapped at 1 mm & new leads (ebay) a pattern coil from a local parts shop (£35) began to fail about a year later - symptom was a slight misfire on wide throttle at lowish revs (maximum cylinder pressures and hence highest plug sparking voltage needed). This time I got stung for a branded Ford coil pack from a main dealer (over £90!) - working OK for just over a year so far with the same leads and plugs (but with gaps now set to 0.9 mm to be on the safe side).
Edited by Dynamic Dave on 07/03/2009 at 14:44
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