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Discussion Starter #1
Okay, this is an annoying one:

2002 Mercury Cougar, 105,000 miles, bought it used about 4 months ago.

Symptoms:
Runs great except, when idling it will skip about every 10 seconds or so (comes and goes sometimes, only happens in gear, either drive or reverse). Happens either warm or cold, also it happens A LOT more when I turn on the front defroster. Also, if the defroster is on I can hear/feel it stutter during cruise (any speed). The stuttering increases with more fan, about every 3 seconds if on highest fan setting. Does not matter if cold or warm air.

Also, the other day I looked at the spark plugs wires in the dark and there is some moderate arcing in the wire, I'll probably have them replaced.

Other symptoms are problems downshifting though this may be a tranny problem (no smokey or burnt fluid yet and it shifts fine, only downshifting under heavy load like going up a hill). Shifts nicely if I push the gas pedal a bit past the point where it would be just about to shift.

Repairs done (in no particular order):
Changed fuel filter
Cleaned/Checked MAF sensor
Checked fuel pump (it has the new cougar pump, not the old bad one)
Had dealer plug it into computer, he said it was OK (and then charged me $150 :banghead:)
Changed oil and filter, put in synthetic 5W-30 oil
Checked air filter (only minor dust, not worth changing IMO)
Checked hoses for cracks, none found
Checked front 3 spark plugs, no problems and they looked recently replaced so I left the hard to reach back ones alone.
Checked the battery
Put in dry gas and fuel injector cleaner (not at same time of course)
Checked belt tensions, all good
Cleaned battery terminals
Reset computer
Listened for engine noises, none that I can hear
Checked fluid levels
Checked overall engine for damage and it looks to be in great shape.

This started happening about 2 months ago and has not really improved or gotten worse. I would like to get this fixed as I like my cars running smoothly.

P.S. Anyone know where the PCV valve is on the cougar, I can't seem to find mine.
 

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Discussion Starter #2
Oh, and it doesn't get worse on anything that's not windshield defrost such as A/C or floor vents.

I'm gonna check the hoses again and check the throttle plate. Anything else you guys can suggest?
 

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The stutter when defrosting is normal on this platform. The A/C clutch is engaged, which dries the air, and it puts a HURT on the engine. This will happen when using the A/C or the Defrost.
 

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Discussion Starter #4
Hmm, thats interesting, okay so the defrost isn't a symptom. Any idea where I should go next to figure out this rough idle? Throttle plate? Ignition wires? Coil? All of the above?
 

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The ignition system on the Duratec is HELLA FINICKY. If you have any arcing at all, you are HOSED.

Buy new plugs AND wires, and replace them all at once. Hopefully the coil pack is OK; they are actually pretty hardy.
 

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Discussion Starter #6
The plugs were replaced just before I bought the car and are in all but brand new condition. Should I still replace them?

Also, the plugs were replaced with platinum plugs (I can get the number if you want it, wrote it down somewhere) but I just read on here that the cougar should have double platinum plugs as it does an alternating firing (igniting exhaust) for emission reasons. So, again, should I replace the plugs?

Also, are there any particular wires you would recommend? I'm looking to keep this inexpensive but I don't want to have to do this again for at least a year or two.
 

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If you saw arcing, your new plugs are toast. Replace everything - bad wires will cook new plugs, and bad plugs will cook new wires. You need to make sure everything is good.

Stock wires are fine. Motorcraft are preferred, but I am using BOSCH right now, and they are fine. I think AutoZone had them for about $53 a set. And be sure to dab a little tune-up grease inside the boots when putting it all back together.

Autolite double platinum plugs will last the longest.
 

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Discussion Starter #8
Just looked under the hood again in the dark this time with someone applying some throttle and noticed some more arcing from the wires to the distributor cap. I assume that replacing these would be prudent as well. Bleh.
 

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It's not a distributor cap. It's a coil pack. Much more expensive.
 

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Discussion Starter #10
Oh, so the distributor cap is in the back then? Bleh, could the arcing have damaged it? I suppose either way I'll check it, time to borrow my boss's multimeter.
 

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Just change the spark plug wires as soon as possible and go from there. They could potentially be causing all your problems.
 

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Just change the spark plug wires as soon as possible and go from there. They could potentially be causing all your problems.
:facepalm: NO; NEVER CHANGE ONLY THE WIRES, especially when you are having misfire issues. Change the plugs AND wires, or you will waste all that money when the bad plugs bake your brand new wires.

That tactic might work on your Corolla, but the Duratec has different needs.
 

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:facepalm: NO; NEVER CHANGE ONLY THE WIRES, especially when you are having misfire issues. Change the plugs AND wires, or you will waste all that money when the bad plugs bake your brand new wires.

That tactic might work on your Corolla, but the Duratec has different needs.
Well, for one thing MightyPirate says the plugs were changed recently. For another, i would like to know how plugs can "bake" wires.

FYI, I've owned 3 duratecs, so I have some experience with them and they don't seem too much different than the other engines I've worked on.
 

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Discussion Starter #14
I think I can answer that myself as well as explain something.

1st off, by recent I mean less than half a year ago.

As for how it can bake it here's my understanding of how it would happen:

Wires go bad and resistance increases causing arcing. Increased resistance in wires cause car to either have to adjust voltage (shortening plug life) or plugs get poor voltage resulting in misfires and improper sparking though I think that it both would only cause reduced lifespan but I'm sure it's possible that the higher voltage would cause the plugs to "cook" on the inside resulting in more resistance (and then causing car to increase voltage, "cooking" wire insulation, back to square 1).

Anyway, that seems unlikely but still possible, besides, with the misfiring is could be a bad plug that's just not showing any exterior problems so changing the plugs would be prudent anyway.

How close am I B3NN3TT?
 

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Well, for one thing MightyPirate says the plugs were changed recently. For another, i would like to know how plugs can "bake" wires.
I've been a member here for 6 years, and on Contour.org for almost that long. I've seen it happen TIME. after TIME. after TIME. after TIME. Not only to me personally, but to countless other people. Far smarter guys than I will tell you the same thing.

Misfires create residue that leaves carbon tracks on the porcelain of the plugs AND on the inside of the plug boots. It scores the finish of the plug; it cannot be wiped away. It renders both useless. If you put a fresh wire on a carbon-tracked plug, it spreads like a cancer into the new wire and kills it in short order. It will run fine for a few days, then the misfires start all over again.

Apparently you have not experienced this problem; be glad. Many have not.

But believe me when I say I'm not talking just to hear my head make noise.
 

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I've been a member here for 6 years, and on Contour.org for almost that long. I've seen it happen TIME. after TIME. after TIME. after TIME. Not only to me personally, but to countless other people. Far smarter guys than I will tell you the same thing.

Misfires create residue that leaves carbon tracks on the porcelain of the plugs AND on the inside of the plug boots. It scores the finish of the plug; it cannot be wiped away. It renders both useless. If you put a fresh wire on a carbon-tracked plug, it spreads like a cancer into the new wire and kills it in short order. It will run fine for a few days, then the misfires start all over again.

Apparently you have not experienced this problem; be glad. Many have not.

But believe me when I say I'm not talking just to hear my head make noise.
The type of misfire that was described in this thread was the type that could be seen while the engine was running and originating from breaks in the wires. The type you have described is from the spark jumping past the plug, which is not visible on a running engine, caused by the gap being too large(not the case here) or an improperly fitting boot. I would still recommend only replacing the wires and not throwing away what probably are good plugs.

I'm also a 6+ year member of Contour.org having been an owner of a '95 SE.
 

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Discussion Starter #17
Okay, help me out with some terminology here. Now, what are the wires running from the coil pack to the back of the engine called? I just for the life of me can't come up with the term to order them. :rolleyes:
 

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Okay, help me out with some terminology here. Now, what are the wires running from the coil pack to the back of the engine called? I just for the life of me can't come up with the term to order them. :rolleyes:
Spark plug wires? Or the harness?
 

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Discussion Starter #19
It's these wires back here (shown in attached pic). Though, now that I think of it I was looking in the dark and I may have just started tracing the wrong wire when I was looking for arcing.

Anyway, I'll look again for arcing and see if it was indeed these wires.
 

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Spark plug wires.
 
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