What's a "Fouled Plug"

[Long Nose]

A newbie question, I know it sounds self explanatory, but would someone mind explaining to me what a fouled plug is? How can you tell by looking at your plug if it is fouled? How does a spark plug become fouled (I assume it has nothing to do with hanging around with sailors

[rick-l]

It is when oil or gas on the ceramic insulator form a conductive path from the center electrode to the body of the plug (ground). Instead of building up voltage and jumping the gap the charge flows through the conductive wet layer and no spark.

[Long Nose]

So the hollow space in the plug is all filled up with gunk?

[Grady Clay]

This is a really good question and disserves a proper answer.

I am lame as he!! Today and way to busy at the moment. First, I suggest you search Pelican (the subject has been discussed a lot) and research all the spark plug manufacturer sites. There is a huge amount of info there.

As you will find, there is not a single simple answer to your question.

There are causes from engine, driving, fuel system, fuel, ignition, choice of sparkplug and much more.

There are results with missing (mis-firing), lower performance, hard starting, stumbling, high emissions, poor fuel economy and much more.

In between you have to diagnose the situation correctly and apply the appropriate solution. It is not always easy.


As everyone posts, please include links so this can be a definitive thread.

Best,
Grady

[Rusty Heap]

Google is your friend. And no such thing as a dumb question.

http://www.ngksparkplugs.com/techinfo/spark_plugs/overviewp5.asp?nav=31000&country=US

http://www.gnttype.org/techarea/engine/plugs.html

[rusnak]

Dry fouling, wet fouling, reading spark plug colors, diagnosing detonation, etc etc:
http://www.4x4review.com/quads/tech/SparkPlugs.asp

Basic definitions, design, and operation:
http://en.wikipedia.org/wiki/Spark_plug

[Long Nose]

Thanks for all of the info - that's great. Here is what was on the NKG Website:

Fouling

- Will occur when spark plug tip temperature is insufficient to burn off carbon, fuel, oil or other deposits;

-Will cause spark to leach to metal shell...no spark across plug gap will cause a misfire;
- Wet-fouled spark plugs must be changed...spark plugs will not fire ;

-Dry-fouled spark plugs can sometimes be cleaned by bringing engine up to operating temperature;

-Before changing fouled spark plugs, be sure to eliminate root
cause of fouling

[fireant911]

This is a really good question and disserves a proper answer.

I am lame as he!! Today and way to busy at the moment. First, I suggest you search Pelican (the subject has been discussed a lot) and research all the spark plug manufacturer sites. There is a huge amount of info there.

As you will find, there is not a single simple answer to your question.

There are causes from engine, driving, fuel system, fuel, ignition, choice of sparkplug and much more.

There are results with missing (mis-firing), lower performance, hard starting, stumbling, high emissions, poor fuel economy and much more.

In between you have to diagnose the situation correctly and apply the appropriate solution. It is not always easy.


As everyone posts, please include links so this can be a definitive thread.

I fail to see how this reply was any help to the original poster. Someone asks a question and your reply is to do a search...

[mca]

Originally Posted by fireant911

I fail to see how this reply was any help to the original poster. Someone asks a question and your reply is to do a search...

Probably not a good idea to diss Grady.

I think that he was simply stating that there are many many possibilities and wanted to make that known at the onset of the thread.

I am sure that he will chime in with additional info where appropriate.

[Long Nose]

I think the point was that if we want this thread to be a Body of Knowledge on fouled plugs, Grady was providing some tips on what to do.

I know I was happy to have Grady reply to this post. I did do a search on this topic before I posted the question, and while there is a lot of reference to fouled plugs, there was little definition on what a fouled plug was.

My mechanic did a tune-up on my car a few months ago to go thru emissions testing, and said I had, among other things, a fouled plug because I was running a No. 5 plug (not a hotter No. 7 plug) and I thought that I understood what that meant. However, I was doing a bit more fine tuning on my carbs, changing jets etc, and thought I would look at my plugs again to see how they looked. It was as I stared at my plugs that I realized that I didn't even know what I was looking for, and thus the question.

I am proud to say that this thread has already provided some enlightenment, thanks to the great links posted. They even have some pictures.



It seems to me that if the porcelin insulator is severely discoloured or coated, either with oil or carbon, that the plug will be fouled. Here are some pictures from the other website.

[fireant911]

Originally Posted by mca

Probably not a good idea to diss Grady.

I, for one, do not believe everything that I have seen posted from that direction.

[rusnak]

Grady has probably forgotten more about Porsches than any of us will ever know, and has helped more people on this board and elsewhere than we will ever befriend. Having said that, my post was in direct response to Grady's. So if mine is helpful than you can thank him.

[Wil Ferch]

"Reading" plugs ... fouled or otherwise...is becoming a lost art with the advent of unleaded fuels. Running unleaded makes for a difficult diagnoses that does not pass the test of older methods in-use when leaded fuels were more common. I suspect that the mal-functioning of a plug would have to be rather severe to see things today. Sure...wet plugs to see if fuel is entering the combustion chamber and not lighting off.....or greasy-oil plugs vs dry-black crustry plugs might indicate oil blow-by and such...but the "color and patina" thing doesn't work well today anymore.

- Wil

[RoninLB]

It starts with a fouled plug and leads into detective work. Even hand cleaning them is a bit more complicated than using Tide.

Most guys don't even know how to warm up a cold engine susceptible to plug fouling or know how to clean off cold start carbon.

So "What's a fouled Plug?" can be an open question beyond getting a shot of penicillin.

[rusnak]

Ronin, I gotta ask, and this is a completely honest question: how do you warm up an engine that is prone to plug fouling? As for cleaning spark plugs, what do you do, apply a drop of muriatic acid or something?

[David E. Clark]

Originally Posted by rusnak

Grady has probably forgotten more about Porsches than any of us will ever know, and has helped more people on this board and elsewhere than we will ever befriend. Having said that, my post was in direct response to Grady's. So if mine is helpful than you can thank him.

A really big +1 from me!

According to a pretty good article on the Automedia website there are three general types of plug fouling:

1. Fuel Fouled: Fuel-fouled plugs may have a shiny coating on the tip and side electrode and indicate a too-rich fuel mixture, ignition problems or a plug heat range that's set too low. First, check to make sure your spark plugs have a heat range that is compatible with your engine (especially if you've made performance modifications). This information is available in your vehicle's owner's manual. To resolve the too-rich fuel mixture, have the fuel injection (or carburetor) adjusted to correct the air/fuel mix.

2. Carbon Fouled: If your plug tip and side electrode are blackened, they have been running with too much fuel (or possibly too cool from a stuck-open thermostat). Other sources of the problem may include bad wiring, leaking injectors, or in some cases the vehicle has been driven at too slow a speed for extended periods of time. The combustion process is not being allowed to have its natural burning-off, or cleaning, effect.

3. Oil Ash Fouled: Engine oil is getting to your plugs, from worn piston rings or valve guides/seals. Get to your mechanic, now.


The Grand National and T-Type Performance Enthusiasts website also has an excellent article called Spark Plug Firing End Analysis that you might want to take a look at. There are lots of good pictures to help you see what you are dealing with.

Finally, there are lots of good articles dealing with diagnosing engine problems by "reading" spark plugs. The Denso website has a good one called basic spark plug knowledge. Hope this helps.

[RoninLB]

Originally Posted by rusnak

: how do you warm up an engine that is prone to plug fouling?

As for cleaning spark plugs, what do you do,

Well.. i use carbs and a rich idle circuit is a way of life. I can't speak for MFI but can only suspect it may be an issue also. CIS should not be an issue.

So I'm starting a cold engine after a few pumps of the pedal. The engine fires and I bring it up to an idle where it'll run clean. A few seconds later I'll raise it to around 1,800. If it's a cold winter start I'll eyeball oil psi and keep the revs low enough to avoid that 90+ oil psi. When the psi drops to around 60psi I'll raise without my neurotic worry.

I never whack the throttle during warm up. I find an rpm and keep a steady pedal. Note that start up carbon is coating the plugs and that a whack to the higher rpms will probably cause the carbon to form a glaze. The glaze can't be cleaned off by driving. When CHT gets around 175F, or about 5min it's time to drive off. I'll be gentle with the pedal for the first 10mi making sure I'm never cruising below 3,000. After that a couple of high rpm pulls and bingo, clean plugs.

There are times when I can't avoid building carbon on the plugs. I'll use a strong solvent and a tooth brush. I'll do my best to clean the carbon way down deep inside the plug where the porcelain meets the shell. If I run into a crust or glazing it's time to change the plugs.



hope that's ok

[safe]

This reminds me of a thing I just heard.
Here in sweden a Porsche Club member had a 911 -69, that prior to a rebuild in 93 had 468.000 miles (750.000 km) on the clock.
That car had used exactly 11 sparkplugs since new!

Apparently he had an unusual cold start technique, he never revved it BELOW 3000 rpm when cold.


Edit:
I can't say if it was a MFI or Carbed car. The whole story sounds to a little to fantastic, I have only heard it second hand.