I have an annoying issue here. My Taurus X (3.5L same as newer Explorer) has a #2 cylinder misfire code (P0302+P0202). I was told by a mechanic, and much research that it was the ignition coil that was to blame. So naturally i replaced it (yes firewall side and center) and …voila! Actually NO, I still have same code, a flashing engine light, and a very rough running engine. BUT… the weirdest part of all is that if I drive the car after sitting overnight its fine, UNTIL you turn it off and back on again (same as before i replaced the coil). Im thinking theres a very slim chance i got a bad coil, so something else is going on. Any thoughts would be great .
Try swapping the coil with one from another cylinder to see if the miss moves with the coil.
If not, try swapping injectors.
If the miss remains at cylinder #2 after swapping coils/injectors, deeper diagnostics is required.
By the way, a flashing Check Engine light indicates that damage to engine/catalytic converter(s) can occur.
Tester
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Concur w/Tester above, the standard diagnostic method for a single cylinder misfire is to swap the components to another cylinder. If the misfire moves, the problem is one of the components swapped. If it doesn’t move, it must be something to do with the cylinder mechanics itself, defective spark plug, valve, compression problem and the like. It seems a simple thing to try is replace that spark plug. Sometimes plugs can get fine cracks in the ceramic insulation, which could well be heat related, and the spark jumps to an engine ground & never makes it to the electrodes. Another simple thing to try is to look under the hood at night in complete darkness, with the engine idling and this symptom happening, see if you notice any unwanted sparks flashing around hither and nether.
What about the spark plugs? Those often get left in for an eternity and can take out plug wires or coils.
With the plugs out I’d run a compression test. If it’s dropping a cylinder that can also cause a misfiring plug which in turn can cause plug wire or coil failures.
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Thanks all, good stuff. So I have the intake manifold off, coils, and plugs out. Tomorrow I will replace ALL the plugs with new iridium, then swap the new #2 coil with another and see what happens. Also, I noticed the #2 plug was far more blackened on the bottom side?
It’s probably some the unburned gasoline – due to the misfire – smoldering on the tip of the plug and creating carbon deposits. Like if you have a smoldering campfire you get a lot of charcoal looking black stuff left in the pit, but a fast burning hot campfire just leaves only gray ashes behind, like the color seen on the other plugs in your photo.
Edit: Is the electrode gap on those plugs you pulled out within the correct range, 0.050 - 0.057 inch I think is the spec for the 3.5L
To the pros here, is there an induction pickup to get a scope pattern on COP ignitions? I went home before COPs were out of warranty.
Oh yes, many. There are any number of COP pickups to get a secondary ignition trace on a handheld scope. I’m a Snap On fiend, so of course I have the kit that you can get for their scopes. I think there are 8 or 10 dedicated leads so I can hook directly to most makes of ignition systems when the COP is accessible.
You can also make a generic one out of foil, duct tape, and some old meter leads I think.
I’m looking at the pictures, and IMO the gap is out of spec, due to normal wear. I’m guessing this car has already racked up some miles
Thanks again guys. Yes the car has about 115k on it. Ok, so now we have 6 new Bosch pregapped plugs installed , and I swapped coils 2 and 4, and still. I have an engine light and a rough engine, however I don’t have a code reader on hand to see if it’s still #2, but I think it’s most probable. After verification, should I proceed to a fuel injector? Or think the worst that it needs a pcm?
Also, I noticed that the packaging for the Bosch plugs says it pre gapped at .044? That seems 10 light to me? Does it matter?
Everywhere I look the gap is specified at .054 which is pretty specific, so yeah, it probably matters. So if the ones you got are pre-gapped at .044, they are probably wrong.
Suggest to measure the gap on the new plugs, perhaps the “.044” on the box is a misprint. In any event if the minimum spec is .050, I doubt .044 would cause any problems other than perhaps some loss of power. Before monkeying with the fuel injectors
- make sure the ecm has been properly reset, then give it enough time to decide if there’s still a misfire
- if there is, determine the exact code so you know which cylinder it is. If it has moved to number 4, then that’s a clue it’s the coil, not the injector. Especially suspect the coil if the gap on the old plugs was bigger than the max spec, as too wide of gap stresses the coils and is probably the most common cause of early coil failure.
- coil tests ok & ecm says there’s still a misfire on number 2? Check compression in number 2.
After all that, then it is probably time to start pulling injectors.
Did you get exactly the plugs listed in the owner’s manual?
I personally doubt it, because I don’t think Ford would specify Bosch brand plugs
I hate to say it, but it might be time to pay for diagnosis. The cause for the misfire might be low compression, damaged wiring to the coil and/or injector, a bad injector, etc.
FWIW . . . a noid lite would tell you if the injector is being correctly pulsed
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Okay so today was fun, I retook out the intake manifold( have that down to a science by now)and re_gapped all the new plugs. And yes the box was correct, they were all at .044. Pretty ridiculous considering it says on the box not to Gap, preset. Anyway, I just ordered a Motorcraft injector will arrive Tuesday, install looks pretty simple. Will update asap. Thanks again all.
Certain types of plugs can’t be re-gapped without risking damage to the plug. Suggest to make sure that’s not the Bosch plug type you’re working with there OP. I think some of the iridium versions have this restriction for example .
The plugs I bought are Bosch 6728 Platinum, was going to do iridium but was told it wasn’t original equipment so I would be ok. Sure hope that’s correct info…
The fine-wire platinum shouldn’t be re-gapped. But for their other platinum types, re-gapping looks to be possible if done correctly.
https://www.boschautoparts.com/en/auto/spark-plugs/platinum-spark-plugs
Yup I should have just spent the extra few bucks on oem. I just purchased 6 new Ford Fine wire factory spec plugs, already pre gapped to .054, will install tonight with new injector. Live and learn …
+1 I’m pretty sure Fords are all Motorcraft plugs…I know my Focus is…