One bad plug

[07EddyB]

I've never seen this before so for the record:
Yesterday the oldest kid comes home from school in my Ex and says the check engine light is on. OK - I hook the scanner to it and it's a bad misfire on #4. No biggie - probably a coil - only one has been replaced in 135K miles so it's about that time. I did have a spare coil - so I put that one in and no difference - still misfires on #4.
OK - the plugs only have 17K on them so it's still probably the coil - the spare one I have might be bad also - it was changed under questionable circumstances.
Fast forward to today - finish work about noon and I switch coils - #2 to #4 and #4 to #2.
Still logging misfires on #4. OK - as much as I hate to pull a plug on this engine it shouldn't be a problem since they have only been in there for 17K miles.
Pulled plug - no obvious issues - go buy new plug - install.
No misfires - very smooth.
I've never had a plug fail in this way. Since I bought the plugs off of Amazon I'm wondering if I got at least one counterfeit plug of the eight - maybe I got more than one. Only time will tell but a plug can apparently fail at only 17K.

 

[94Eddie]

New parts can, and will, fail. Sounds like you were just the unlucky person to buy the part that failed. It is hard to see why such a simple part as a spark plug would fail at all.

 

[Rcflyer330]

yeah it can happen. I had a similar story with my v6 where I had a motorcraft spark plug bought from advance auto parts fail in about the same amount of miles. except I didn't have any codes to go off the vehicle would just start jerking while under load but only with a very specific set of conditions. I actually thought it was the transmission failing. long story short I found out it was actually a misfire on cylinder 2. after I replaced all the plugs again the issue never came back and that was probably 50k miles ago.

 

[apoctank]

At least it came out in one piece. Just wait until you have one break on you

 

[Bazz270]

What was the spark plug gap on the bad one?
Carbon on the electrode?

 

[07EddyB]

Here is the business end of it. I wiped it off but didn't 'clean' it.

 

[07EddyB]

As for breaking plugs I've been extremely lucky so far. Here is the first change at about 80K:

 

[Bazz270]

Here is the business end of it. I wiped it off but didn't 'clean' it.

View attachment 434193

If u still interested to verify the defective spark concern, connect this spark plug to the coil (connected to vehicle harness) and see the spark coming out of the electrode (spark thread touches the engine).

If you can see the spark and the spark gap is ok the problem is not your spark plug...

 

[07EddyB]

If u still interested to verify the defective spark concern, connect this spark plug to the coil (connected to vehicle harness) and see the spark coming out of the electrode (spark thread touches the engine).

If you can see the spark and the spark gap is ok the problem is not your spark plug...

That's true - I've done it to a lot of small engines that had running issues. That's usually because you suspect the coil so you have to confirm that it's getting fire. In this case, I had swapped a spare coil on and then swapped coils again and the problem didn't move. Upon pulling the plug there was no visual evidence that something was preventing it from firing. It looks pretty good as you can see above.
So it's likely the plug - but maybe a wiring issue to the coil. A store less than two miles from me sells new plugs and less than $15 is a valid price for a diagnostic swap so that was the easy way out.
I really have no interest in a situation like this to confirm that the plug was bad when replacing it solved the problem.
I do understand your point though - there have been situations in the past where I've done that sort of thing. In this case I just decided not to over think it.