Odd burn pattern on spark plugs

96 Vortec · September 20, 2006

This is regarding a '96 K1500 w/ the 5.7L Vortec engine.

I have a misfire in #3 (P0303). The plug is crusty with a small black buildup on one side, but looks perfectly normal on the other side of the plug.

The first thing I did was a full tune up. Next was a compression test, which showed everything to be normal. Since I thought oil was leaking into the cylinders I had a machine shop change the valve stem seals with the heads left in place. The machine shop said the seals were unbroken/untorn and were still rubbery and pliable. On a diagnostic machine the fuel system showed normal pressure. And the oil is black as night ruling out a head gasket leak.

When the plugs are out, they have oil on the threads. I got to talking with a co-worker yesterday and came up with a different idea to what's going on. When the machine shop put the valve covers back on, they didn't replace the gaskets. I'm thinking now that I have a clogged fuel injector which is causing a poor spray pattern. I think the oil on the threads is from a leaking valve cover gasket.

The only other possiblity I can think of is bad rings, which can be hidden during a compression test. The only real way to rule out the rings is with a pressure test, which I have not yet done. But I don't think it is the rings based on the odd burn pattern on the plugs.

I'd appreciate any ideas or input to the problem I'm looking at.

Also, based on some research here, if it is a fuel injector, how hard is it to replace. I saw mention of having them cleaned at the dealership, would this be a likely solution to my problem?

95Sierra2500 · September 20, 2006

Having them cleaned at a dealership is a relatively cheap solution as it's around $150. Injector replacement is around $400 (for one injector) and usually ISN'T the problem. Things to check are a clogged catalytic converter, cracked cap (can happen with a brand new one), or a bad wire (also can be bad, even brand new).

96 Vortec · September 20, 2006

I've checked everything twice. I also forgot to mention the misfire is only noticable at idle. While driving I notice no loss of power. And I also recently changed the EGR valve.

Based on my continuing research, Check post #3

Do misfires caused by bad wires and caps lead to a black buildup on plugs?

*edit*

I don't know if this is related or not, but I've recently started leaking electricity. The 105 amp alternator was recently tested under load to put out 62 amps. I replaced it but the voltage guage did not change it's behaviour. It reads 14V at startup but seems to run down to 13 or so volts on my commute home. It only reads lower voltage at idle, on the hiway it reads slightly below 14. Until a month ago, the guage never left it's perch at just a tick over 14 unless the truck was turned off.

GM-Tech · September 20, 2006

How long have the plugs been in there? You can have excellent compression and still have bad/stuck oil control rings as these do not contribute to compression.

Injectors almost always set a P0300 (random misfire). Never seen one set the single cylinder misfire code. I'd look to the ignition system.

96 Vortec · September 20, 2006

When the SES light first came on and I took it to a shop, the plugs had been in the engine for 50,000 miles. In the last 5000 miles I have changed the #3 plug twice.

Where in the ignition system should I start?

Would a misfire cause the buildup on the spark plugs? Especially a buildup on only one side of the plug?

asilverblazer · September 20, 2006

Might it not be getting enough electricity to the plug to properly ignite fuel/air mixture. Some sort of relation to your mentioned alternator (though that should affect any random cylinder)

GM-Tech · September 20, 2006

Where in the ignition system should I start?

Would a misfire cause the buildup on the spark plugs? Especially a buildup on only one side of the plug?

<{POST_SNAPBACK}>

I don't know where you should start in the ignition system. If you've already replaced the plug and wire, that only leaves the coil, cap.

I also don't know why it would only get black on one side. Probably related somehow to the swirling of combustion gases. Yes, the plug would get somewhat fouled if it's misfiring, though it's usually the whole thing, not half.

Can you get a GOOD, high resolution close up picture of the plug? I can tell by looking at it if it's oil, but the photo has to be excellent quality.

96 Vortec · September 21, 2006

(click for pics)

Cylinder #1 - photo 1

Cylinder #1 - photo 2

Cylinder #3 - photo 1

Cylinder #3 - photo 2

Here are the best pics I could get. I posted the plug from cylinder #1 because that is how the problem with #3 started and what it has progressed to. #1 & #5 look very similar. #7 looks perfectly normal at last check. All even numbered cylinders look completely normal as well.

Both plugs in the pictures have a less than 3000 thousand miles on them. Cap, rotor and fuel filter were changed during the tune up.

GM-Tech · September 21, 2006

The photos are not that great (sorry!), but from what I can tell, it sure looks like oil deposits to me. Since there's no lead in fuel anymore, there's nothing else that could leave that level of deposits. Too rich would leave black, sooty deposits. Plug #3, photo #2 is especially revealing with the deposits on the outer electrode... at least it looks that way, but as I said, it ain't all that clear.

It's possible the tech botched the valve seal installation. Wouldn't be first time. If they didn't use the protector on the valve stem, they could nick or tear the seal as it passes over the keyway. Or they didn't get it seated and it has lifted off the valve guide. On the other hand, if it's the same cylinders as before replacing the seals, the odds that the exact same cylinder seals were damaged is pretty unlikely. Could also be worn guides, but I can't say I've seen that as an oil control problem.

The other options are oil control rings, cylinder wall damage or an intake gasket leak on the bottom side allowing it to suck oil in. Also, look at the PCV and make sure it's not full of oil, though I think that wouldn't affect just those cylinders.

96 Vortec · September 25, 2006

Is there a way to test the oil control ring or is it a problem only proven/disproven by pulling the piston to inspect the ring?

I have to ask, since the problem originated in #3, but has spread to #1 and #5, would it be more likely that the intake gasket or possibly the head gasket are the source of the problem?

Thanks everyone for all the help so far.

GM-Tech · September 25, 2006

Even looking directly at the oil control ring(s) in your hand, you probably wouldn't be able to detect anything wrong with them. You could measure ring end gap to see if they're collapsed, but the most common problem is them being seized in the piston by carbon buildup. You'd also want to check cylinder taper, things like that.

Yes, I'd say the intake gasket could be the trouble. No, the head/head gasket are not involved in any kind of oil issues. No oil goes through the head in a way that could get into a cylinder.

96 Vortec · September 25, 2006

So is my only real option to pull the intake manifold and inspect the gaskets. If I don't find any evidence of a problem, reassemble and the problem persists, I know it's the rings?

GM-Tech · September 25, 2006

So is my only real option to pull the intake manifold and inspect the gaskets. If I don't find any evidence of a problem, reassemble and the problem persists, I know it's the rings?

<{POST_SNAPBACK}>

Sounds like a plan.