Changing Plugs/Coils-do them all?

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I'm nearing 100K on my MKZ with the 3.5L Duratech, and I'm suspecting it would benefit from plugs at a minimum. Experience with other cars tells me that coils can start going in the 125K range.

Here's what I'm debating on this:

In general, I hate doing plugs on transverse mounted V engines. It looks like this one will need to have the intake manifold off. I've read procedures, although admittedly not watched videos on it to see difficult those back 3 plugs will be to access. The 3 front ones I'm not expecting too much trouble. Of course the coils will need to come out to get to the plugs, so with that in mind I'm considering a couple of options:

1. Do plugs only and cross that bridge when I come to it with coils

2. Replace the back 3 coils, the save the front ones for as-needed

3. Just bite the bullet and do it all

To be honest, options 2 and 3 are most appealing to me. Experience with other cars has told me that aftermarket coils can be hit or miss and I've had Autozone ones fail in 6 months(fortunately on a modular V8, which is a 10 minute swap). The last time I did a job with difficult coil access, I did Motorcraft coils, which hurt but I felt good about them lasting. Going that route isn't cheap, though.

In my situation, what would you all do?
 
How much do the coils run? Perhaps do the rears as insurance.
I have had exactly 1 COP coil fail in my experience. 2006 TSX with about 150K as I recall.

Don't tell anybody, but I bought a set for our trusty 2001 Tundra V8, just because of miles.
They screwed up a wonderfully running engine. Don't ask me if they were fakes... Thanks in advance.
 
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IMO, change the plugs (Motorcraft only) and if able, change the coil boots and springs.
As said, coils are better than they used to be, and failures are usually caused by poor spark, either wide gaps or a short (bad boot/spring).

And yes, if you decide to replace the coils, only use OEM, otherwise you will be doing them again very soon.
 
Had a GS400 and changed coils only when they get bad, due to ease of access and being cheap. They all went bad within 15k miles and I was under the hood 8 separate times to replace them. From there on I just replace all at once and be done with it.
 
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I never change coils before they fail. Keep a spare on hand. I did have to change all 8 on my Jeep once. They were falling apart when I changed the plugs.
 
Thanks everyone.

Basically I've dealt with COP changes myself on two separate vehicles:a couple of the Town Cars my mom had and then my Lincoln LS.

The Town Car was easy as could be with the 4.6L longitudinal Modular. Pop off the vanity cover, and if I remember right the coils were literally right there. Undo the one bolt holding it in place, pull it out, put the new back in, and you were done after plugging it in and bolting it down. When it would throw a CEL and feel like a misfire, I'd pull the code which inevitably would be "Misfire Cylinder X", then just change that coil.

The LS was still a longitudinal V8(AJ-V8), but for one it was a bit bulkier up top than the SOHC Modular, plus that engine bay was packed a lot tighter.

The whole coil issue with it was interesting. I knew it was running rough, but it actually got to be dangerous to drive. It would misfire, then throw up "Engine Power Reduced" and go into limp home mode. More than once it happened when I hit the gas to merge onto the interstate, and fortunately when it happened I was able to pull over, shut it off and restart it, and it was fine. It did it to me twice and I parked it for higher speed driving until I could figure it out/fix it. I had Autozone pull the codes on it, and it returned a bunch that were throttle body related. What the guys on the LS forum told me is that it was likely one of the front 2 coils(on either side of the throttle body) on their way out, and apparently it was known that stray RF from them could cause the throttle body electronics to react wonky, which in turn would make the car think there was a throttle body issue and it would pull engine power to prevent runaway acceleration(even though the throttle body was actually fine). Considering that at the time there were a few reports of issues in other makes electronic throttle body cars, I was actually glad that this one was smart enough to shut it down if it sensed a problem.

All of that aside, I bit the bullet to the tune of $600 on a set of 8 Motorcraft coils, and I remember having to remove quite a bit of stuff to access some of the rearmost ones. I was glad I'd done all of that, and the car "woke up" with more power and a better throttle response than I ever remember it having.

In any case, looks like the manifold isn't terrible as per the above video, so I'll probably go grab plugs in the next couple of days and do it.

As a side note, someone above mentioned "Motorcraft Only." I have switched essentially to only using NGK plugs, and of course with type/specced tipping material for the vehicle. Is there a reason to NOT use NGK plugs(which I've always thought of as among the best around) in this?
 
I've had to replace 2 of the 3 rear coils on the 3.5 in my Flex. Not a hard job and doesnt take much time to remove or reinstall the intake.
 
Thought I'd follow up on this one to say that I FINALLY got this done earlier this week(thanks hackers who shut down my work with ransomware...)

I did NGK Ruthenium RX Plugs, and only changed the coil boots.

Plenum removal wasn't a huge deal, as the video above shows. It's certainly not like changing the plugs on longitudinal OHV inline engine, but other than a few stubborn hoses it wasn't a big deal.

I did of course do a general clean-up on everything. I used painters tape to cover the intake runners as soon as I pulled the plenum just to be safe on those, then blasted everything with compressed air and swept out a lot of junk. I also blasted out the plug wells while I still had the old plugs installed(wouldn't do that with plugs out...). I don't know if any of that matters, but I felt good about it, and I figured if nothing else having everything as clean as I can get it in my home garage makes it less likely for something that doesn't belong to end up in the cylinders while a plug is out, or to end up in the runners.

I did notice a decent bit of oil in the plenum, although none past the throttle body. I've read a lot of "It's normal" to some other "You should change your PCV" and then some "An OEM PCV will last 200K miles if you change your oil regularly." I'm going to change it anyway for good measure, although I wish I'd ordered it with everything else considering that access was easy with the plenum off and I'm guessing won't be so easy with it on. Fortunately Rock Auto has the Motorcraft one for ~$40(vs $70 for what the local places want).

Also, I cleaned up the throttle body. I ended up taking it off as there was some crud on the back of it in the throat. It was moderately stubborn, but did move with carburetor cleaner and blue towels(although I helped things along a bit with a nylon brush).

Fortunately, the oil all stopped at the throttle body, and I didn't find any in the intake. I've read this is a less bad thing. I work on modern cars infrequently enough that I don't always know exactly what to expect, and on old British stuff if there's not oil everywhere you look it's probably out :) .

I ordered new plenum gaskets. The old ones seemed fine when I took it off, but since I had them I figured why not. I know these aren't old cork or paper gaskets, but I still like to avoid reusing gaskets as much as I can and had ordered since I didn't know what I'd find.

Overall, the engine seems a bit more responsive although the idle still isn't as smooth as I'd expect this engine to be(or remember it being in the past). I'd actually kind of forgotten to look at the air filter in a while, and I'm going to grab one today and change it. I did blow the old one out while I had it out, but I know I really should change it.
 
Generally coils are not a normal service item. Sure they could fail next week or they could last 20+ years. But I don't like playing "what if" games so I leave coils alone until they act up or fail. The engine will run with 1 bad coil and I'll replace the bad one. Injectors and coils are equally likely to fail... nobody talks about injectors until they fail, but many will replace a coil that is still working perfectly fine.

Spark plugs of course are a regular service item, good you got those done.
 
BTW, the plugs I pulled were chalky white, or maybe just the barest hint of brown.

The other modern(ish) plugs I've pulled seemed to generally run a fair bit darker. Not sooty black, but maybe toast colored. They're definitely darker than where I generally try to get carbureted cars, where I shoot for a light tan ground strap. If I'd pulled the plugs from the MKZ out of my MG, I'd have been richening the carbs. I'll post a photo here in a bit.

Does this sound normal or is something amiss? I know in theory between the MAF, O2 sensors, and multi-port injection that modern vehicles run pretty close to stoichiometric, although IIRC also they will periodically flip-flop between slightly rich and slightly lean. Of course I could also be totally off, and these plugs, at 93K miles, are fresher than when I've changed in the past on modern.
 
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