I’ve been overdue for a tune-up, and since it’s a used car (and doesn’t get looked after by the dealership), I want check up on a few things myself.
Tonight’s my time to check on the spark plugs, clean them up, make sure they’re still good and such. I take out each spark plug individually, brush off soot, check the gaps, and put them back in. After the work is done, I take the car for a test drive around the block. Knocking, pinging, and the check engine light all greet me in a nice warm chorus. By the end of the drive a terrible burning smell permeates the car.
How nice! But WTF? Why would this happen?
Some things to note:
2.2L OHV engine, inline, four cylinders.
Spark plug number four was dropped on the ground – are they fragile enough to be damaged by this?
Some dust may have got into one or more of the cylinders, as I unfortunately have to work outdoors.
I’ve done this work before with my girlfriend’s dad, but this is the first time I’ve attempted alone, and on my car.
The wires are going to the right place (they’re all numbered, and if I had one wrong, another wouldn’t reach), and as far as I can tell they’re all solidly connected. The ceramic on the plug isn’t cracked.
The only thing I did was make sure the plugs has the right gap, according to my Haynes manual. If the manual is wrong, could the plugs be misfiring? If I did get some dust into the cylinder, could that even be a cause of the trouble? I have no idea where to even begin.
If the only thing you did was remove and replace the plugs, and you’re sure the plug wire routing is correct, the only plausible explanation I can think of is that some or all of the plugs are damaged. I would suspect this happened from the brushing off of soot and/or the dropping of the one plug.
I seldom clean plugs (a new plug costs less than the labor to clean it), but when I need to I do it with spray carb cleaner and compressed air. I never let anything solid - like a brush bristle - touch the internal ceramic, because it can mess it up.
A dropped plug can sustain a crack that affects its performance even though it can’t be seen.
It’s very rare to find improper plug gap data in any repair manual. Nevertheless, the proper gap is on the emission information sticker in the engine compartment. New plugs should be (ideally) at or (acceptably) within .002" of the spec. The gap will widen with wear, and typically when it’s about .010" greater than it was new it’s time to replace it. There’s really no need to regap them within their normal service life, and probably no benefit from it.
Normally the internal ceramic color will be in the white to light tan range. If it’s actually sooty, there’s a significant problem that needs to be addressed.
Dust in the cylinder is not particularly desirable, but it won’t be there long and it won’t cause the type of problem you describe. Debris of any sort in the spark plug hole threads, or especially on the sealing surface of the head at the top of those threads, is a concern. It should be carefully wiped clean.
Lightly coating the spark plugs’ threads with anti-seize compound helps ensure they won’t seize into the head. This isn’t a particularly common problem, but it’s not rare either, and it can really, really suck. An ounce of prevention…
Not that this applies here, but I have personlly seen an incorrect spark plug wire routing diagram once. I only caught it because I was working out of two manuals at the same time and noticed they had different diagrams.
Due to some problem inside the cylinder the air fuel mixture is either pre or post combusting. In other words, the air fuel mixture is either lighting off by itself before the plug sould fire, or after the plug fires, the mixture is detonating not burning.
I second (third?) it’s probably the plugs.
However it could be the plug wires were damaged when you removed them.
Does your engine have a distributor or is it a coil pack engine?
No. The main concern with overtightening is that they might be hell to get out. It’s possible it could mess up or strip the threads in the head, but that would take really severe overtightening.
You give backyard mechanics too much credit, at least as far as not wrecking aluminum heads goes. I’ve seen the aftermath of a few jobs where the sparkplug threads were stripped clean out of the head, leaving a nearly smooth bore, all nice and ready to have a helicoil inserted.
One notable fool I knew tried to duct-tape the plug in place because the engine compression kept popping it out.