Hi, my Stilo Abarth suddenly has a warning light and alarm last week which said Engine Control System Failure and although the car was still running when it happened, as soon as I slowed down to stop the car was juddering. Cutting a long story short, the car went to the dealer who hooked it up to the diagnostic machine and the fault was an ignition coil failure. This was replaced and I collected the car.

The car now has no warning light on but it was definitely not running as it should and is mis-firing slightly. I rang the dealer back up who said that it is possible that the coil they fitted is faulty but that what can happen is that when one coil goes it sets off a sort of chain reaction and that it might be a recommendation to change all 5 of the coils. This is obviously an expensive option and I have arranged for the car to go back in for further testing but can anyone advise me as to whether they too have been advised to have all the coils changed at one time or is the garage looking at making some money (sorry, that sounds a bit cynical!)?

a chain reaction? what a load of crap. i've replaced dozens of faulty coils and never needed to replace them all. you only replace a coil if it is faulty, one faulty coil will not affect the others.

Well that was my thought too but then I know less than nothing about car mechanics! What i thought about asking them to do is just replace the coil they fitted last week with a new one and see if it was just faulty - if that doesn't sort the problem I guess they will have to try each one in turn do you think?

Simple enough to check to see which coil is faulty, just by pulling out the plug to each one in turn as the engine idles - the one that doesn't change the engine idle note is the faulty one.

if it was me i would get a multimeter and measure the resistance of each coils' primary and secondary winding, then you can see how they compare and decide if they are all well matched. if there is a difference of more than 10% in any coil it can lead to uneven running (a slight misfire as you described), if they are all within 10% of each other then you can be pretty certain they are all ok.

unfortunately very few dealerships have someone who is willing and able to do that kind of diagnosis, so they will probably play the coil swapping game and hope to get lucky, or if they're really lucky the examiner machine will tell them which cylinder the slight misfire is occuring on, although that is unlikely considering the light has gone out.

its also possible they didn't put it back together correctly and the problem will magically disappear when they take it apart and do it properly, who knows.

if you drove the car for some time with the faulty coil it could even be a simple problem such as the ecu still trying to compensate for the dead coil, if you replace the faulty coil and do not reset the ecu (disconnect battery for a hour) then it can take a few journeys for the ecu to re-adapt and go back to normal ignition timing.

Oh right, thanks for the advise - so if they charge me loads to test them I'll know I'm being "had" !! It's already cost me £124 to have the diagnostic and the replacement coil but as it didn't return the car to its former state (albeit it isn't juddering at idle and the light has gone off - prior to this suddenly happening the car was running great and has only done 33,000miles) then i feel they need to tell me what the problem is without charging me again unless they find it is a completely different problem.

PS I only drove the car a further 2 miles after the warning came on and the car was recovered to the garage.

£124 - so that would include time on examiner, diagnosis, fitting and the cost of the coil.

OR you could have just replaced it, or got a competent friend/member to do it, for the cost of the coil itself, around £36 or so.

Hopefully they will sort it out quickly for you, with minimal cost.

I'm a female Stu - we panic when cars go wrong and we need them for work hence we are in the hands of the professionals! :-D

If I had known it wasn't likely a major fault I could perhaps have looked around for a competent person to fix it for me but when a warning light suddenly comes on and an alarm sounds when I'm doing 70ish mph on a motorway then I assume the worst!

I hope they fix it too with minimal injury to my bank account, I'll let you know - it goes in this afternoon.

Many thanks to you and Jug for the advice

jug said:

a chain reaction? what a load of crap. i've replaced dozens of faulty coils and never needed to replace them all. you only replace a coil if it is faulty, one faulty coil will not affect the others.

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Ditto. I never know Stilo Abarth's had 5 coils!

Most Easterly Panda's said:

Ditto. I never know Stilo Abarth's had 5 coils!

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The 5 cylinder ones do

Don't forget your plugs!
A too big a spak plug gap causes huge electrical stress in the coils, the insulation breaks down, and bzzzt! duff coil. The wires inside the coil are as thin as a hair so it doesn't take much

That's why people think it's a "chain reaction" in that when one goes- they all seem to go but often it's because they've all been under so much stress jumping that too big spark plug gap that they're all just to about to die. If the spark can't jump the gap then the voltage has to go somewhere. So have your spark plug gaps checked or just put new plugs in, they're cheap enough.

Plugs arent checked routinely at services and are only changed at 40k km intervals last time i looked. That's way too long for single pole plugs on high energy coils

Stu DemonD said:

The 5 cylinder ones do

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That would make sence

i had a coil go in my 4cylinder stilo. and the garage replaced 3 coils cos they said the one that went set off the others. i didnt believe them at the time. next time i'll just replace the coils myself.

so, what is the gap on abarths? 0.8 or 0.9?


since my car servicing (in which they replaced the plugs for identical ones) the idling shakes a bit in the morning. NKG Champions.


I did not try to put the old ones back because I do not have the tool to remove them. Could I have the wrong gap?