Only one spark plug is getting carbon fouled?

Maintenance/Repairs
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1

Hey guys,

My 2001 V6 mustang cylinder 4 spark plug has been repeatedly getting carbon fouled. I have changed that spark plug twice now in the past month due to it fouling out. Today I noticed car was hesitating/stumbling so I removed the cylinder 4 plug and sure enough it had a ton of carbon on it. This plug is only a week old. The same thing happened to the brand new plug before that. I checked a couple other plugs and they had a small amount of carbon on them but nothing abnormal. Only cylinder 4 is having this problem.

I have already tried the following in the past monthā€¦

-Used iridium and platinum plugs the first and second time changing them respectively, and used ones specifically meant for my car.

-Changed the coil pack a month ago before replacing the first set of plugs

-Replaced both upstream O2 sensors

-Cleaned the MAF sensor

-Put a new K&N filter on my cold air intake

-Replaced the fuel injector for cylinder 4

-Ran a bottle of fuel system cleaner and also a bottle of cataclean through the gas tank

-Replaced the coolant temperature sensor

There are no check engine light codes.

Despite doing all these things, I removed cylinder 4ā€™s plug again today and found it was covered in matte black residue (carbon) I am positive it is carbon and not oil as the plug is not wet at all.

I cleaned the spark plug and put it back in. Also today, I just replaced the fuel pressure regulator an hour ago and hoping this fixes my issue.

I know carbon fouled plug(s) indicate a rich condition but I have now done everything that could be causing the issue. I removed the other plugs and they have a very small amount of carbon on them except cylinder 4 plug which continues to get a lot of carbon buildup. Any suggestions for things I havenā€™t tried yet? Am I likely looking at an internal engine problem?

2

Try running a slightly hotter spark plug in that cylinder.

Tester

3

I have thought about that and will probably try that next. I just canā€™t think of WHY only that one plug is getting fouled and not all of them.

Is there any other part that I havenā€™t listed that could be the culprit? I just did the fuel pressure regulator today so only time will tell if that fixed the issue

4

Although it is rarely confined to one cylinder, I wonder if the valve stem seals for that cylinder may be defective.

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5

Run a dry and wet compression test on that cylinder. You may be losing one; or all of them actually and those deposits could be oil instead of gasoline.

Just my 2 cents, but a compression test is mandatory with any engine suffering a performance problem, fouled plugs, dead misses, and so on.

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6

Smell the plug to see if it smells like gas or oil.

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7

Wouldnā€™t low compression in a cylinder almost always throw a code? I donā€™t have any codes

8

There is no low compression code. There is no sensor to measure that. You might see a misfire code and it could be intermittent. Leave that plug in a while longer and you are highly likely to see a misfire code set.

You canā€™t rely on the cars computer to tell you everything that is wrong. It isnā€™t that smart. Sometimes you have to go back to the basics. Vacuum tests and compression tests.

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9

Maybe this will help

1008Ɨ768 167 KB

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10

If you do a google for fouled plugs, one of the first things that comes up is ā€œif #4 is fouling, check valve guidesā€. Not that anyone on the internet knows what they are talking about.

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You mean everyone but you and me Iā€™m sure.

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Me anyway.

13

Recently came across this myself while replacing my plugs.

My question is, why does only one side of the plug show buildup?

From the Champion website:

ā€œIf the deposits are on one side of the plug, this is an indication of upper engine wear (valves, seals, cylinder head). If the deposits appear all around the electrode, this usually means lower engine wear (cylinder, pistons).ā€

So what is the logic/rationale behind this? (specifically for one side of the plug, but all around would be helpful to know as well).

Assuming itā€™s valve seals (which I suspect in my case), does it have to do with the way the plug is oriented in the head? One side of the electrode will always be _________ ? Or something to do with gravity and the leaking oil?

Thanks for any and all help in understanding this, hereā€™s a pic of my plug.

Deposits one side plug

14

Did only one plug look like that or all of them??
Are you using additives in the engine or gas tank?? fuel system treatment every fill up??
Are you running cheap gas??

Spark plug indexing is not your issueā€¦ Looks a lot like cheap fuel or too many additives being usedā€¦ Or maybe even the wrong spark plug for your vehicleā€¦

Lastly, the plugs you posted a pic of look like standard spark plugs, are they the correct spark plugs for your Mustang?? You did not mention the year make and model of the vehicle in questionā€¦

15

Gulpā€¦apologies, I responded to this post before knowing that (some of) the forums are vehicle-specific! The engine in question here is a Nissan V6. But your symptom of one plug getting fouled is similar to my issue, and I was hoping to find a ā€œone-size-fits-allā€ explanation!

To give more info:

Did only one plug look like that or all of them??
Just the one plug (#6, closest to firewall on this engine)
Are you using additives in the engine or gas tank?? fuel system treatment every fill up??
No additives or treatments
Are you running cheap gas??
Yesā€¦Kroger, QT, Shell

These plugs were the incorrect one for the vehicle in that they were ceramic (30k mile) and it calls for platinum (100k). It was my mistake, I ordered the wrong ones. They were installed about 3 years and 20k miles ago.

As I look at the image more, it seems like (possibly) oil is leaking past the valve stem seal (intake? exhaust? both?) and eventually settles on this particular side/region of the electrode, and over time, this is the area where the oil is getting ā€œfusedā€ to the plug during ignition. Or is that way off?

(Thanks for your reply, I can ask that this be moved to a more appropriate forum if need be!)

16

Well, I got the Make out of you, how about the year and model, V6 is good as long as only one was an option, if not then the size would be nice alsoā€¦ ie 2010 Nissan Frontier V6ā€¦

Do you get any blue/grey ish smoke at start up, and then goes away after sitting overnight??

I would correctly run a dry/wet compression test on the engine and compare cylinders, while I had all the spark plugs out and installing the correct new OEM spark plugs (NGK or Denso) NOT an OE Type they are not the sameā€¦ If I new what you had I could give you the correct part numberā€¦ Do not buy from eBay/Amazon, to many fakes out thereā€¦

IF the vehicle has a distributor, then check and replace the cap and rotor and probably needs a good set of ignition wires, again, it helps to know what you haveā€¦

17

Find the pcv valve and follow its vacuum hose. It may connect to the intake feeding directly to the problem cylinder.

18

Ok, all, the full rundown!

2002 Nissan Frontier, 3.3L V6

I was getting a misfire/stumble on acceleration (at times felt like a shudder) with no codes, then EVENTUALLY a code would pop up which showed #2 misfire, so that led me to change the plugs (which I thought shouldnā€™t need changing since they were SUPPOSED to be 100k plugs, until I realized they werenā€™t!)

So I bought the correct plugs and installed them (NGK), and upon inspection of the old plugs came across that abnormal one.

Yep, definitely smokes more on startup, I would say more greyish than blue. Sometimes it clears up after running a few minutes, sometimes it lasts longer than I think it should (I look at other tailpipes and think ā€˜why is mine still smokingā€™?) but I will monitor that more closely now.

Rod, will ā€œfollowā€ your suggestion about the PCV valve!

A YouTube guru on the Nissan VG33 said this plug is more prone to fouling because the oil pools up more in this part of the head due to a flawed design, and points to valve seals.

Iā€™m intrigued as to why it leaves this particular pattern on the electrode, and I canā€™t find a similar image on the webs showing that same pattern. The closest I find are always under the ā€œAsh Depositsā€ sections of how to read plugs.

Sorry to be so worry, Iā€™ll get better!

Oh, dave, the distributor was just replaced recently by a transmission shop. The vehicle would buck randomly (no codes) and I thought it was the trans. But they couldnā€™t get it to restart and determined it was the dizzy. (Shortly thereafter the MAF sensor threw a code and I replaced itā€¦vehicle has around 251k miles).

19

OK thanksā€¦ I have replaced and sold a lot of Dizzyā€™s on Nissans 3.3L engines, top bearing/bushing goes bad and starts getting metal shavings on the top (under rotor button) and allowing the shaft to walk around, that being said, make sure it came with a new cap & rotorā€¦

When was the last time the ignition wires were replaced??

If you decide to replace the valve stem seals, replace them allā€¦

Spark plug Manufacturer Part Number: PFR5G-11 (NGK 2647)

I would run some Marvel Mystery Oil (per the directions) in the engine oilā€¦ Drive it a while and pull a plug and see what it looks likeā€¦

20

All of my vehicles are dizzy equipped. I sometimes use my timing light for this sort of thing. If I suspect a spark problem on a certain cylinder I compared the timing light pattern on that wire, compared to the timing light on a wire going to a cylinder with no spark plug fouling. I just compare the frequency and brightness of the flashes cylinder to cylinder.