I have a 1999 Ford Ranger XLT ext cab. V6 4.0L I got the truck in 2003 and ever since. I would get a misfire. I find out which cylinder (almost ALWAYS on driver's side) and change the plug. Several months later same thing, maybe a different cylinder on Left side. I started using an ohm meter and finding that when the misfire happens, the plug show some continuity. Nobody can tell me why this happens. I replaced the splash guards in the wheel well thinking maybe some how cold water splashes up on the plugs, but this keeps happening. Doesn't matter the brand or cost of the plugs, the high dollar jobs mess up as well as the $2 ones. I have no clue as to even how spark plugs go bad like this. To date, I have changed out bad plugs 11 times!

Rob

 

I've read here that you should be using double platinum or all copper.

 

Was doing that. Still ended with the same problem. Went with cheaper ones recently to cut down the cost.

 

Cylinders
1 5
2 6
3 4
Are matched pairs, they share 1 coil in the coil pack, and both spark at the same time

4.0l coil pack firing order is
3 4
2 6
1 5
front

Any relationship on the failed spark plugs and pairs?

Mentioned it because it could be the coil pack

Need gap of 0.054

Motorcraft are best, Autolite next

Spark plug wires can also cause this but would expect that to be cylinder/wire specific.

Can't see the spark plug tip?

Is the electrode and tip OK?

Fuel injector could as well but again would be same cylinder each time.

And no pinging or knocking ever, just the misfire?

 

Tip and plug look fine. Gap is correct.
its always 4,5,6 that go bad. At least those 3 easy to get to.

 

It might be a long shot, but check your grounds, namely from engine to frame and frame to battery. Bad grounds can cause all sorts of crazy crap.

I would imagine that it would be possible that the coil itself is going bad on one bank and delivering one heck of a spark.

 

Good pictures here of the differences in wear from one bank to the other: https://www.ranger-forums.com/4-0l-o...0-sohc-119625/

Spark plugs are designed to spark from center to tip, the most wear would be on the tip with this method of spark.
So single platinum(iridium) spark plugs usually have the coating on the tip, to make them last longer.

With Ford's Waste Spark system two spark plugs are wired in Series, so one spark plug sparks from center to tip and the OTHER spark plug sparks from tip to center, reverse spark.
Bank 1(1,2,3) is center to tip
Bank 2(4,5,6) is tip to center

So Bank 2 would wear out faster than Bank 1 if single platinum was used

As shown in the pictures in above link

This would take time, so may not be your problem, but look at the spark plug centers to see if they are being worn down more than they should.

 

Wondering if you have either a cracked head or bad intake manifold gasket causing over lean mixture causeing that bank to run hotter damaging spark plugs in the process. Temporary solution try running colder plugs in that bank. Have you scanned your motor for any issues? Compression Check? Coolant temperature Right?

 

It's back... yes the same misfire problem. Oddly enough this thing misfired bad for 15 miles, I pulled off 3 times, hooked up my code reader, no pending code, no active code/or SES light. I will have to pull the plugs and find the bad one on my own. Why is the comp not giving me at least a pending code? I shut off the truck 3 times that like 4 trips total.

Do I just need an exorcist?

 

Well... I pulled the plugs the one I changed when I created this post. ohms out the same as the one I replaced. The gap was fine. Here are pics. this is the new plug thats only been in for what a few weeks??

 

Okay got a new coil.. the motorcraft one from Rockauto. Installted, ran great for 3 days.. then it rained...back to misfiring. I don't know what is getting wet. I didnt' even drive to any excessive water.

 

I have replaced countless sparkplugs over the years. I have worked side by side with I am guessing over 100 mechanic - technicians over the years.

And not once have I seen a single spark plug go bad like yours has that wasn't physically damaged- dropped in shipping or handling or during installation.

There is no mystery here, change the source where your buying the sparkplugs from.
And change the method or tools your using to replace the plugs.

This is just my opinion that it is either operator error or the plugs your installing are getting to you damaged.

 

That was my thinking too, I never seen this before. Only had issues when a plug actually worn out. I tried different stores and brands. Even was careful when checking the gap to make sure wasn't a lot of pressure used. Installing, is easy on this side of the motor, used normal sparkplug socket and just made sure they were snug.

 

This may or may not help this is just what I do.

I use a gutted old spark plug boot and 3/8 extension to install the plug.

Then like most people I use a spark plug socket but I never use a spark plug socket that still has the rubber insert in it.

I have seen way too many spark plugs get damaged because of the insert.

I am not saying this is your problem for sure.

If your using a cheap socket with the rubber insert, toss that socket out and spend the money, get a good quality socket and remove the rubber insert.

A Craftsman brand at minimum should be used, Snap on, MAC, Matco ETC would even be better yet not completely necessary if your on a tight budget.

Also the type of ratchet- extensions swivels etc your using may come into play.

I find the spark plugs that are easy to get to are the ones we tend to rush through and easily damage.

Whenever possible I like to use a good quality long handle flex head ratchet with the right extension and good quality close tolerance socket setup that will allow me to have one hand on the ratchet handle and my other hand at the head of the ratchet.

This will help prevent the socket from tipping side to side while tightening the spark plug.

If you have done this and are still having the problem I do not know what the problem is.

 

I have the same problem with my 2000 ranger, 4.0 XLT. I have been fouling plugs for last two years, replacing them when my engine begins to misfire. My mechanic is certain it is a cracked head, though I am still getting correct compression in all my cylinders. initially, he and i were going to continue just replacing plugs, but the fouling had gotten Worse and more frequent, so Based on his recommendations, he is going to replace both heads. Hoping that fixes the problem. I will post the results, though between my mechanic, my research and my father, all indications point to cracked blocks.

 

You should do wires and new plugs.

 

Sorry, I neglected to add all the other things I did replace... wires(2x), plugs(4x), as well as Electronic distributor pack1x.

 

Did you ever get to check earths?

It was a little coincidental that after raining (regardless of severity) that it occurred again.

 

 

Any updates on if replacing the heads fixed the problem or did you ever get around to commiting to that? I have a 2000 4.0 xlt 4x4 that keeps doing the same thing. Engine runs good when plugs are fresh but keep fouling out one or another and engine misfires and runs rough. Just trying to figure out what the best route here to take. Thanks

 

The computer threw a code for bad O2 sensor driver's side. Oddly enough I change this one according to my records about 4 years ago with the OEM Motorcraft sensor.
Evidently it was bad from the start, just not bad enough the throw a code. knew it would be something simple.. but given I had changed it and the others didn't look at O2s anymore.

ROb.

 

i had the same problem cylinder number 3 would last about 6 months I switched to platinum ir fusion plugs with the 4 prongs on it instead of 1 and they last alot longer

 

so i have had my 2011 4.0 v6 for a few months ago and replaced my spark plugs 3 weeks ago. And the moment the job was done a ticking noise comes from the engine compartment
recently spark plug 4 has started blowing out of the socket while driving i screw it back in then a few hundred miles later it blows right out and yesterday cylinder 6 has started blowing out but when attempting to crew it back in it won't catch i have even tried new spark plugs and they are the motorcraft coper oem ones any suggestion
and if the ticking get too loud that is when the spark plug blows out still in boot

 

Sounds like the threads are shot in the head, you can use a heli-coil or an insert to repair it.

 

The "tick" is from a spark "jumping a gap" so you have a bad spark plug wire, its called "arcing", its what's suppose to happen inside the cylinder at the tip of the spark plug, but can happen anywhere along a spark plug wire if it has broken insulation(arcs to engine metal) or conductor is broken, jumps the gap, can even be at the boot if metal conductor is not fully on the metal spark plug tip

4.0l SOHC was never known for spark plugs unscrewing themselves
Since they didn't "blow out" for the month(4 weeks) prior to you changing them then it would have to be something that happened when you changed the spark plugs 3 weeks ago, since its only taken maximum 3 weeks for the problem to occur

Are the spark plugs the same brand and number of the ones you removed?

Were any of the old spark plugs harder than the others to remove(cross threaded)?