Same Spark Plug Fouling Every Few Months?!?!

[MrBobDobalina]

Okay everyone, I haven't posted or been on here for a while. I got super busy with work and fortunately the T4R has been running solid for the most part....

Pretty much since I owned it however the same plug fouls every few months.

At first I bought a whole new set of plugs not realizing it was the same plug each time. Per this link: 1999 Toyota Firing Orders - Its the #4 (on the non-coil side in the middle.) I am pretty confused as to what could cause this same exact plug to foul randomly EVERY-TIME!!!

I drive the truck very lightly - I rarely push the gas pedal hard (knowing its a T4R and not a car.) Even though I have the Supercharger I can just feather the gas and still get places quick!!!

So I will just randomly start her up and when I go to drive it will misfire like crazy...I will replace that exact #4 plug and will be instantly good to go for an unknown amount of weeks.

Any trouble shooting advice would be great!! She runs so smooth otherwise.

ALSO - I AM RUNNING NGK PLUGS THAT ARE ONE STEP COLDER THAN STOCK - PER SUPERCHARGER.

Thanks again everyone, I really appreciate the help!!!!

 

[IanB]

I would swap the coils around and see if the plug fouling follows a coil pack. It's free diagnostics, worth a try.

 

[NOT ME OR SOMEBODY]

I hope I am wrong

Are you losing any anti freeze?

I had an fj80 that would do the same thing and it was the head
Gasket. Anti freeze in the cylinder = fouled plug

 

[004runnerLtd]

My last truck (Ford Ranger) did this same exact thing...had to replace the same spark plug every 3-4 months, as it would start jerking.

Hate to say it, but it's most likely low compression in that particular cylinder.

Go have a compression test done by a mechanic, and see if there's low compression in that cylinder.

 

[Drcoffee]

Hate to say it, but it's most likely low compression in that particular cylinder.

Go have a compression test done by a mechanic, and see if there's low compression in that cylinder.

+1 Either bad rings or valves. Do you have a picture of the fouled plug. The color will tell you oil, water or gas. If it looks dry, could be an injector.

 

[jakknz]

Pictures would help us to help diagnose it. Take a look at this link: Spark Plug Analysis
Does your plug look similiar to any pictures on there? A clean looking (white) plug indicates coolant, oil fouled will indicate blow-by meaning bad piston rings.

 

[MrBobDobalina]

I would swap the coils around and see if the plug fouling follows a coil pack. It's free diagnostics, worth a try.

Okay, this is solid advice. I will do this today, just in case. Thanks!!

Are you losing any anti freeze?

I had an fj80 that would do the same thing and it was the head
Gasket. Anti freeze in the cylinder = fouled plug

Sadly, yes I am losing a very small amount from the overflow bottle every few months as well. I have not been bale to find a drop of coolant anywhere as well. This is leading me to believe there could also be a head gasket issue. I am going to look more into a compression and leak down test ASAP.

My last truck (Ford Ranger) did this same exact thing...had to replace the same spark plug every 3-4 months, as it would start jerking.

Hate to say it, but it's most likely low compression in that particular cylinder.

Go have a compression test done by a mechanic, and see if there's low compression in that cylinder.

Yea, I am afraid you are all probably onto the actual issue at hand here. Possible HG!!! Ughhh!!

+1 Either bad rings or valves. Do you have a picture of the fouled plug. The color will tell you oil, water or gas. If it looks dry, could be an injector.

I am attaching a picture of the plugs for reference.

Pictures would help us to help diagnose it. Take a look at this link: Spark Plug Analysis
Does your plug look similiar to any pictures on there? A clean looking (white) plug indicates coolant, oil fouled will indicate blow-by meaning bad piston rings.

Well the plugs started out darker when I started replacing them, the last 2 plugs are a bit whiter....Another indicator of possible HG.


So this issue is frustrating, because the truck seems to run solid and accelerates very smooth and quick with just feathering the gas...

EVERYONE - Thanks again for the support and advice, gotta love the T4R forum!!!

 

[Socco]

FWIW: Before you jump to bad rings...

I had an Astro that would foul 1 plug so badly that if I drove 200 miles on the highway, I would have to change that plug to get home. Many hours of diagnostics by myself and a shop turned up nothing. Only when I was swapping out the V6 to a V8 I found the culprit. A hard plastic vacuum line on top of the manifold had split down the underside and curled inward.

 

[jakknz]

Your next move should be a leak down test on all your cylinders. A compression test is good but a leak down test imho is better. It will allow either you or the mechanic to actually hear where the air may be escaping to. A headgasket issue, for example, may cause bubbling air in the radiator or you may hear air escaping from an adjacent spark plug tube.

Your fifth spark plug from the left, if changed at the same time as the others, looks a little suspect with it being that white. Was that what the fouled plug looked like when you took it out?

 

[MrBobDobalina]

FWIW: Before you jump to bad rings...

I had an Astro that would foul 1 plug so badly that if I drove 200 miles on the highway, I would have to change that plug to get home. Many hours of diagnostics by myself and a shop turned up nothing. Only when I was swapping out the V6 to a V8 I found the culprit. A hard plastic vacuum line on top of the manifold had split down the underside and curled inward.

Hey that is a really good point. I need to get a vacuum gauge on this as well and verify that...

Your next move should be a leak down test on all your cylinders. A compression test is good but a leak down test imho is better. It will allow either you or the mechanic to actually hear where the air may be escaping to. A headgasket issue, for example, may cause bubbling air in the radiator or you may hear air escaping from an adjacent spark plug tube.

Your fifth spark plug from the left, if changed at the same time as the others, looks a little suspect with it being that white. Was that what the fouled plug looked like when you took it out?

I plan on doing a leak-down test this weekend or Monday with a friend...I will post that up once done.

The plugs are all actually from the same cylinder. That is my collection of them. From oldest to newest (Left-Right.) When I first had the issue I wasn't realizing it was only that one plug and I was driving it a bit more not really knowing all that was going on. First 2 times, I replaced all the plugs. Now I get a miss, turn the truck around and swap that exact plug in a few minutes and back on the road.

Thanks again everyone for the advice!!!!