Spark plug colour

[marlinh]

I pulled these plugs out of one of my cars and am wondering why two of these plugs are so white, cyl 2 and 4.



Here is a close up of #4. These plugs have 10,000 km on them.



Any suggestions?

[Jooseppi Luna]

According to my Haynes, this would suggest running too hot. They suggest that it would most likely be due to overadvanced ignition timing or lean running.

Interesting that it is occurring on only two cylinders.

[dlb]

if it was all of them i think it would be pretty straightforward but the fact it's only 2 and 4 is odd. another member here had an issue with rough running and noticed the #1 plug was black and soaking wet. it turned out the be the manifold vacuum port on the first intake runner sucking gas through a ruptured AAP. i can't think of what could cause vacuum leaks on 2 and 4 though, besides a loose or cracked manifold. maybe pull the carb and confirm all the bolts are snug.

the other thing i am thinking is that perhaps the rotor and/or cap are worn in such a way that they are making contact on the 2nd and 4th too early.

how does this engine run, overall? what made you pull the plugs in the first place?

[marlinh]

The engine runs pretty good overall. It lost a bit of coolant and no external signs that were obvious, so I pulled the plugs to have a look.

[Mark]

I think it's just a bit of ash from burning oil. They don't look bad to me. Pretty much all of mine look like that when I pull them.

[Petros]

I vote that those two cylinders are running more lean than the others. this would be either from a leaky or cracked intake manifold, or if there are any vac lines that go to that part of the intake manifold have a vac leak. the number 4 would be the likely the power brake booster line. you may have a leaky hose or a leak in the booster.

easiest test is to do a drop down test, with the engine idling, pull each spark plug wire one at a time and notice the idle speed drop. It it drops the same on all, it is not enough to worry about (a hand held rpm gauge is useful for this). If the two "lean" cylinders drop little or no rpm compared to the others, your fuel mixture is too lean in those two.

Double check the resisance rating is the same on all 4 plugs, just to rule out that they might be different and cause that.