Took the time today before ripping out some subflooring at the in-law's and changed out the spark plugs. Should have done so sooner. All 8 looked similar. I don't think they look bad but I've not gotten much guidance on reading plugs so feel free to chime in if you're reading this. Two plugs are below and i can get pictures of the rest later if requested.
Hello Termite,
The more you put into plug reading, the more really valuable 'actionable info'
can be yours. Instead of trying to weave all of the following into a coherent
report, I think it will be easier to to give you a bulleted list. Here goes:
1) On a
single cylinder engine, it's all about the gap, color/deposits on the
porcelain center conductor, signs of distress during previous installation
(cracked porcelain due to mechanic overtightening, or gap way too big or electrode
smashed into the center conductor due to ham-****** install, correct heat range plug
too loose, couldn't conduct heat to water jacket, or even a too hot/too cold heat
range installed.)
IF you discover that the original spark plug was a victim of a bad installation,
get what (little) you can from reading that plug, write it
down for future reference & discard the old plug.
Now install the correct new plug carefully...and after running this new plug for
approximately a thousand miles (or equivalent number of hours on the meter)
or so, pull it...and *NOW* you really have something worth reading.
More on this in a bit.
2) On a
multi-cylinder engine, there's an additional troubleshooting dimension
to take advantage of when it comes to reading spark plugs -- it's all about
the
pattern matching. (!)
This is
so important to figuring out if you have one, a pair, a bank, or even
all cylinders needing attention in a V6 or V8 engine that I wanted to
make this it's own bullet.
To help yourself (and those of us looking over your shoulder) the single
biggest thing you can do is to lay the plugs out exactly as they
were installed in your engine. Try & organize the plugs so that
they are all laying in such a way that we can read/compare
the insulators of all 8 plugs against
each other. (Take a quick look at
something I recently posted in order to see what I'm trying to describe.)
Here are a few examples to demonstrate how this works:
* All 8 cylinders proper coloration, they all match each other,
GOOD.
* All 8 cylinders too rich / too lean / too hot / too cold...but
they ALL still look identical to each other. Global external issue
that affects all cylinders. (all too lean = possible fuel pump
pressure/quantity issue, all too rich = one or more sensors
lying to computer throwing off fueling, etc)
* 7 cylinders matching, 1 outlier. If you go back to the picture I
posted, 7 cylinders were pretty close to each other (given the
220K miles plus unknown spark plug mileage. But I did notice
that the #6 cylinder was dirtier than the rest? I didn't know why
at the time...but when I
did find the root cause the #6 plug
confirmed my diagnosis. Anyway, with the "only 1 bad cylinder'
scenario, it tightens up the list of possible perpetrators. (1 bad
spark circuit, 1 bad injector, a vacuum leak affecting only 1
cylinder, etc.)
* 6 cylinders matching, 2 adjacent bad. Let's say hypothetically
the spark plugs in cylinders #5 & #7 look bad, but the other
6 all match & look reasonable. Time & again further checking
uncovers a blown head gasket between these physically
adjacent cylinders.
* 1 bank (4 cylinders) bad, other bank good? One possible
answer might be that you have a failed/plugged cat or
wonky O2 sensor affecting one bank but not the other.
(Cross-correlation for one bank of good plugs and a second
bank of poorly-colored plugs would be if you were to get a
P0151 code for a wonky O2 sensor on one side, but at the
same time no codes for the upstream O2 sensor on the
other side, etc.)
****
As you can see, there are many possible failure patterns
in a multi-cylinder engine...and IF you are on the lookout
for them, then you will be miles ahead of your neighbor
who just takes the old plugs out & chucks them into the
trashcan after briefly examining each one individually.
Seriously, if you take out all the original plugs, with unknown
mileage, and unknown installation practices, etc., there's
enough talent here to give you a decent
guess as to what's
going on. (Especially if you have the accompanying Check
Engine codes and/or detailed driveability observations.)
But wait, there's more! If YOU install a fresh set of plugs,
do all the normal maintenance stuff (fresh oil, known good
coolant, thermostat, etc) ...drive it for a thousand miles,
pull those plugs, and share that photo, then we will
*absolutely* have real data (with controlled variables)
to work with and be better able to advise you.
(This combustion quality info slathered all over your plugs
is coming
directly from the combustion chamber...and I am
of the belief that the further you get away from the
combustion chamber, the more you are now playing 'the telephone
game' with the data being reported to you.)
In summary, the problem with spark plug reading is that
most mechanics don't take the time/modest effort to
understand/control the variables surrounding spark plug
data, so they don't see the all-important failure patterns
in a multi-cylinder powerplant.
So many people jump to the conclusion that troubleshooting an
8 cylinder engine is 8x harder than fixing a single cylinder engine.
I disagree. If you use the Complexity of the System against
itself, the easier it is to get all the cylinders to share the load identically...
and in the end that's what it's all about.
****
And yes, I still need to discuss the coloring thing. I
will deliver that in my next post.
Cheers --
