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Spark Plugs Darker on 2,4,6 vs 1,3,5

 

On my 2000 Eurovan (12 valve engine), plugs, coil, and wires all replaced about 3 years / 8k miles ago.

I just removed the six sparkplugs to see how things look:

Plugs #1,3,5 look very similar to each other and, to my eye, look perfect.
Plugs #2,4,6 look very similar to each other, but quite a bit darker.

Any theory what could cause this?

On the VR6, what do cylinders 1,3,5 vs. 2,4,6 have in common?

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I'd be looking for a vacuum leak most likely, perhaps on the intake gasket.

If you look and find nothing there, maybe you've got some dirty or plugged injectors, but it would be unusual to have 3 of them plugged just the same so that you got such consistent bimodal results.
 

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Injectors: I don't know the history on this van, but I suspect they have never been replaced, but I agree with you it that the 135 pattern is unlikely.

I found??which says the VR6 has two camshafts, one for 1,3,5 and another for 2,4,6, and that timing chain issues could cause this pattern of burning.

(I probably should have mentioned this) Though I changed the plugs 8k miles ago, I just had the timing chain replaced (about 200 miles ago).

Maybe the uneven burn pattern could be due to timing chain wear over the prior 8000 miles, which has now been fixed? ?

Subjectively, I think the van is running a little smoother after the chains were done.

I should have checked the plugs before getting the timing chain done!




On Jun 27, 2024, at 12:23?PM, Joshua Van Tol <jvantol@...> wrote:

I'd be looking for a vacuum leak most likely, perhaps on the intake gasket.

If you look and find nothing there, maybe you've got some dirty or plugged injectors, but it would be unusual to have 3 of them plugged just the same so that you got such consistent bimodal results.

 

I like this theory about the timing chain, it makes sense. If it were my van, I'd not worry about it any further, unless it gives you reason to. But do inspect the plugs next time they're out.

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