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A friend of mine has a 98 Chevy S10 2.2L pickup. Every couple hundred miles, he’ll get a cylinder 2 misfire. Upon pulling the spark plug, we can see that the center electrode is melted and fused with the ground (side) electrode. This has happened about 5 times already. He did tell me that before this began happening, the cylinder 2 spark plug blew out of the head. He put in a helicoil and has been having this problem pretty much ever since.
Could it be that the plug is unable to transfer heat/ground properly because of the helicoil, causing the center electrode to melt? He tells me there are no other abnormal symptoms and the truck runs great until it finally begins misfiring again. All the other spark plugs look good. Or perhaps it is a symptom of a bad coil pack?
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Just a guess here:
When the firing end of the plug has overheated, the ceramics may break or the electrodes may melt.
Under usual engine condition, the plug does not overheat. Note, however, that it gets extremely hot in the case of abnormal combustion (ex. high – speed knocking, pre – ignition).When the A – F setting is lean due to a faulty fuel system, the combustion temperature may rise, resulting in abnormal combustion. The engines cooling system may be faulty. When the spark timing is too early, the combustion temperature may rise, resulting in abnormal combustion. When deposits (generating from combustion) are accumulated in the combustion chamber, the combustion temperature may rise, resulting in abnormal combustion.
When deposits have accumulated on the firing end of the plug, deposits may overheat, causing abnormal combustion. Especially in a two – cycle engine, oil gets burned and remains in the combustion chamber as deposits, accumulating on the plug as well. It is necessary to remove these deposits periodically.
In engines that consume larger amounts of oil, oil may enter the combustion chamber. It is necessary to check the amount of deposits during inspection of the plug. Burning of oil can also be detected by visible white exhaust gas emitted from the tail pipe.
The car is either running to lean, or has to much ignition advance, or both.
Make sure your using the right grade of gas, and get the timing and mixture checked ASAP.If it was running lean, wouldn’t it be happening to more than just the one plug? As far as deposits on the end of the plug – they would have to be building up REALLY quickly. The plug melts within a few hundred miles. I think he checked compression and it was good. None of the plugs, including the one that melts, appear to have deposits.
I’m pretty sure he’s using 87 octane. I’ll tell him to play closer attention for spark knock and see if we can check the timing. Thanks.
Sounds like the thread repair is hampering the stock plug’s ability to shed heat at the proper rate. He could try going to a colder plug, one heat range cooler, to see how things work. If that doesn’t cure the issue, keep on trying even cooler plugs. You want to arrive at a condition where the plug runs cool enough so that it doesn’t melt, but still runs hot enough to keep getting fouled with oil and other deposits.
This will require a bit of research on plug specs.
That sounds like an interesting solution to me.
He tells me there is no spark knock, it runs like a charm before the plug melts. No misfires, no shaking like it’s out of time.. nothing. If it was out of time or running lean there would be other symptoms, correct?
He said he was going to change the fuel filter, but I don’t see how that could effect just one plug. I’ll recommend trying cooler plugs and see what happens. Only other thing I could think would be if the number 2 fuel injector wasn’t putting out the amount of fuel that it should, thus causing a lean condition in that cylinder. Maybe we can try swapping injectors with another cylinder too. Thanks.
First off the chev 2.2L should only have the delco $6 a plug plugs or NKG plugs. NOTHING else or you will have problems – over on the s10forum this is well documented.
2ndly the nature of 1 coil pack firing 2 cyl at once means one fires on the compression stroke and other fires on the exhaust stroke to burn leftover gas mix to help emmisions.
could it be possible that cyl injector is sticky or leaky causing more fuel to be burned on that cyl?
Yes I just thought of that before seeing your post. Perhaps we can try swapping injectors around and seeing what happens.
Just so we’re clear, what I meant was trying a cooler plug on that cylinder only. No sense in swapping out all the plugs if the other cylinders are running fine.
It’s also possible that the threaded insert hasn’t been driven all the way home, and the top of it is preventing the plug from seating fully against the cylinder head. This would cause the plug to retain heat rather than conducting it away.
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