Plugs or Coil Pack or O2 or combo?

[Denethor]

It's probably getting time to change the plugs anyway, but let me throw out there the symptoms and get a consensus from the masses on here.
Regular fuel regardless of octane, I've tried tanks of 87-93. Under hard acceleration I get #8 cyl mis-fire code and sometimes #3 but rarely.
If I run Flex Fuel and keep the tank 51% or more Ethanol, no mis-fires what so ever BUT when idling in traffic for long periods or just idling in park, i get a check engine light for catalytic converter out of range (I assume this is due to the alcohol burning so clean there is not enough difference from front O2 sensor to the rear one??). On the OBDC the cats do run very cool on flex fuel vs pump gas.
Last year I had the very common issue where the heater hose gets a leak in that T connector so the COPS got soaked and might have been damaged.
Ford mechanic friend said don't replace the COPS unless you know they are bad because a good portion of new ones are DOA. Another local mechanic said do both while you have them out.

Any thoughts on why no mis-fires on Flex and why Flex causes Cat issues?
Any way to ensure a COP is good?

Thank you.

Also MPG suffers GREATLY with Flex making the cost savings not worth it.

 

[JExpedition07]

If you had the heater t-connector leak soaking plug wells it not only wrecks coils but damages plug performance as well.

 

[1955moose]

There's 2 ways to check a coil. One is pull it, get out your volt/ohm meter, and measure both primary and secondary resistance. Specs online. Second way is swap suspect bad coil to cylinder next to it, if misfire code moves, bad coil. That leaking hose shorted out #8 coil. You can buy a set of the Accel or other sets of 8 coils, keep a few of the old Ford ones around in case of failure of new one. Or buy a set of Motorcraft ones for around $70.00 for set, save a few. As far as your cat, you'll need to run fuel trims, and determine if it's a cat, a vacuum leak, or bad 02 sensor. Don't know why the alternative fuel works better than gas, maybe the octane, or whatever's in it, fools the cats and computer.

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[Denethor]

If you had the heater t-connector leak soaking plug wells it not only wrecks coils but damages plug performance as well.

The heater hose leak was over a year ago, and its on the odd number side of the engine, so it "could" explain the random #3 but not the rest.

 

[JExpedition07]

The heater hose leak was over a year ago, and its on the odd number side of the engine, so it "could" explain the random #3 but not the rest.

Very true, I’m sure others will chime in. In my experience when I get a specific misfire I replace everything spark related on that cylinder. Most view this as a waste and diagnose more.

 

[1955moose]

Their is no odd side as the driver's side is 5,6,7,8. Your thinking of GM products . You didn't say where the coolant leak was, I took a shot. Coolant leaks can get under the cop plug, and never go away. My advice is to pull all the plug connectors and spray them out with electrical cleaner. Do the same with boots on each. A simple bit of coolant in there, will have you chasing your tail for weeks trying to get rid of miss. Same goes for any corrosion if not cleaned up. Electricity needs a clear path, or resistance builds up, and current can't flow. Same goes for battery, pull terminals wire brush both ends, put a barrier after. You'll get it fixed.

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[Denethor]

Yes, sorry, I mis-spoke, I meant the even cyl8 side is opposite the hose that always leaks at the T connector but the odd Cyl3 was right near the leak. I'll do some testing on the cops when it warms up a little outside.

 

[1955moose]

No worries. The boot or spark plug may be your problem on #8. If #3 got wet, then your probably sunk on that coil. Try cleaning and testing both before buying a new one. The original Ford coils are pretty tough. On most coils 1-2 thousand ohms for primary test, and 8-11 thousand on secondary side. Best bet, test one of known good ones, compare to suspect bad one. Easiest way to know if a parts good.

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[TobyU]

As Moose said, pull them out (an might as well do plugs if you sad it needs it) Blow out the plug wells with compressed air really well. Replace the rubber boots and make sure the springs inside them are dry. Then reinstall. I would put #8 in one of the easy to get to front positions 1,2,5, or 6 then see if all is well or if you miss moves.

I am a fan of the $30 sets of ebay coils because I have had good luck so far with them. I do however keep a box full of oem and often like new replacements I pull out of fords though.

 

[Adieu]

The heater hose leak was over a year ago, and its on the odd number side of the engine, so it "could" explain the random #3 but not the rest.

It's not even-odd

It's 1-2-3-4 front to back passenger side, 5-6-7-8 front to back driver side

Most obvious place for heater hoses to mess things up is COPS #2 & #3, but who knows


#8 (driver side, closest to driver) could ostensibly get flooded while topping off coolant or something

 

[ManUpOrShutUp]

Any way to ensure a COP is good?

Yes. https://easyautodiagnostics.com/ford/4.6L-5.4L/how-to-test-the-cop-coils-1

 

[TobyU]

Sorry but that guy is applying too many other engine and car principles to the ford COP and saying they are rules when it just doesn't play out that way in real life on fords.
In the book and online are one thing BUT.

You do not need a spark tester. I disagree. An old plug works fine BUT. I don't put much faith in checking COPs this way anyway.

I am all about the cylinder balance test but I prefer to cancel out COPs not injectors but either way works but mine is better ...read on.
It is easy to spot a dead one but often they are intermittent.
Unplugging and plugging in COP is better because I have seen several that was dead miss after 2-3 good fires. Each time you plugged unplugged it...as soon as you plugged it back in it was smooth as silk for 2-3 seconds then solid miss.

I have never damaged a COP from using spark plug or allowing it to spark by pulling it up off of plug...but I see little reason to do this.
These are far more durable than that. They misfire and get wet and short out and do that for hours and weeks and still coils are good!

Any ohming out tests are a very basic test and can't be trusted in real use when hot and firing over and over etc.

Best way is code scanner and look at mode $6 results for misfire counts on repeated scans after clearing codes each time.

Then go to suspected ones from results and unhook connectors and reconnect seeing if you get short amount of no missing but too often it is not missing when you are testing it.

Back to mode 6 and swap a couple to different locations to see it if moves.

Also, if you have done it recently, you should always pull coils up and blow strong compressed air into plug wells to get moisture/coolant, leaves, sticks, twigs and dirt out of there.

 

[rjdelp7]

Driving with that misfire, caused catalytic converter damage. That is why your getting Cat below threshold.

 

[TobyU]

Driving with that misfire, caused catalytic converter damage. That is why your getting Cat below threshold.

Exactly. I have bought several vehicles that would pop the code because they have been driven with a misfire. If it's not too bad it hasn't melted and plugged the converter you don't have to replace it. And usually you don't. I have had good luck running three to four bottles of 91% isopropyl alcohol and with the gas down below a quarter of a tank. This seems to clean the converter and make the code stay away longer.