My #3 spark plug keeps fouling. What do i do?

[mb3offroadr]

i have a 99 ranger 4.0 and in the last year i have fouled my #3 spark plug about 3 times. any ideas on what could be causing this?
thanks in advance
mat

 

[Sevensecondsuv]

Bad fuel injector maybe.

 

[Bob Ayers]

Bad plug wire, bad valve guide seals, or bad rings.

 

[Will]

Doubtful on the rings or stem seal being as it is just one cylinder. Wire or injector are a good start.

 

[shadetree]

How is it fouling? Is it carboned up, caked with white stuff, or just not working?shady

 

[Evan]

If the injector is sticking in the open position, it will foul the plug. That happened to me on #4.

If you have a leaky valve guide on the intake or exhaust port for that cylinder, you will end up with a fouled plug.

I would guess it's one of the above that's causing your plug to foul.

 

[dieseltweaker]

mine kept doing that and i had had a small leak in my head gasket and it eventually blew out.

 

[UrbanRedneckKid]

Mine's doin the same thing. when i put the engine(used) in I did a tune up on it. #3 was fouled and had traces of oil on it. I'm thinkin it's a stem seal, cause I have a little poof of smoke when I first start it up.

Can you give anymore details about yours?? How does the plug look?

 

[Danger06Ranger]

Seriously, they might help.

 

[MikeMcC]

Guys if this is the 4.0 OHV It's extremely likely you have a cracked head or blown head gasket. This is a common problem on all 4.0 OHV's. The tale tell sign is if you are getting a little bit of white smoke on start up.

If would recommend a compression test. You will probably have low compression on the cylinder that keeps fouling plugs.

If replacing the plug fixes the problem for a short time but it comes back, you know it's nothing ignition related, and it's something thats actually fouling the plug. In this case It's almost a 100% certainty that you have a blown gasket/cracked head.

Ways to check for a blown head gasket/cracked head:
1. Slowly loosing coolant.
2. Smoke at start up.
3. Rough Idle.
4. Fouling spark plugs on a regular basis.
5. Inspect the block for coolant leaks around the heads, and pull the spark plugs after they have been sitting for a while to inspect for coolant.
6. Check for coolant for presence of oil.
7. Send your oil off for a used oil analysis. If it comes back with coolant contamination it's most likely a head/gasket.

If it matters I also have a 99' 4.0L that was fouling on #3. Turned out to be a cracked head.

 

[UrbanRedneckKid]

Don't tell me that. Who wants to hear that??

Sad, but very true. These heads are REALLY known for cracks.

Fortunately for me and I already properly diagnosed mine. Mines not a headgasket/ head prob.