Termite's 95 K2500 Suburban

[HotWheelsBurban]

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.

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Nice to see I'm not the only one that takes them out and marks what cylinder they came from! I mark the new one too, right before it gets anti seize on its threads and goes in the hole( gap checked first). I didn't have a chance to look closely at the plugs out of Rawhide (which I'm sure are the original ones) when I changed them, because I had to head out with my friend who's moving, to work at his place. He actually was waiting for me while I changed the last 3 plugs! But I kept them, so they can be looked at later. From what I recall though, they didn't look too bad for 120K.

 

[Road Trip]

And yes, I still need to discuss the coloring thing. I
will deliver that in my next post.

Cheers --

Alright,

How about if we put up something to look at before I start up
with all the chit-chat?

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Here's some bullets to ponder while looking at those tortured spark plug photos above:

* I found this on an Aviation website. They run specific fuels & oils with specific additives,
etc. Here on the ground, in the land of computer-controlled engines that stay in a tight
feedback (closed) loop, you will really have to work at it in order to get a GMT400 engine to
deviate very far from spark plug photo #1 above.

* With today's calibrations, I find that most plugs are closer to a bone white than a light tan.
(And if you take the cylinder heads off the faces of the exhaust valves are also a similar
bone white.)

* Dry black soot is normally way too rich. (think leaky/dribbly injector, especially if one 1 plug
is sooty & the other 7 are a pretty tan.)

* Oil burning is more bluish than straight carbon black, especially if there is a lot of engine
oil residue on the spark plug threads?

* In water cooled engines, you can actually end up with a spark plug that looks too clean,
too new...as if it had been thoughtfully steamed cleaned for your viewing pleasure?

This is a case where too clean is too bad, for it usually means that coolant is making it
into the combustion chamber & being turned into steam by the heat of combustion.
(Coolant is being sourced from either a blown head gasket between cooling jacket
& combustion chamber, crack in the cylinder head itself, or even a coolant leak from
one of the 4 corner intake manifold coolant passages & being sucked into the adjacent
intake port, etc.)

I have personally troubleshot to the 'too clean = bad scene' scenario. A hint of blush, tan,
or bone white is preferable to squeaky clean. (especially when the other 7 have normal combustion
deposits deposited) NOTE: With iron heads + cast iron manifolds this was pretty rare...but
when they left the cast iron heads in place & bridged the gap between them with an
aluminum intake manifold, we started seeing this a whole lot more often after 50-75K miles
of driving. (The whole dissimilar Coefficient of Thermal Expansion rates stressing/distorting
the gaskets with every single thermal cycle. (!)

* Small shiny spots on the insulator (aka: peppering) are tiny bits of aluminum piston
being ablated from the piston face & a small percentage is being deposited on the
spark plug ceramic. (And the rest is going out the exhaust valve!)

Simply put, too greedy / too much timing / too lean at max throttle and this is
how the engine tries to drop you the hint to either Knock It Off or I'll have no
choice but to hole one or more pistons.

Peppered plugs means that you are definitely on the Hero to Zero trajectory.

****

There's always more...but this is plenty of food for thought in order to start
the journey to help revive the disappearing art of internal combustion
engine spark plug reading.

You know, the old guys were raised to read the plugs, while the next generation
start with the cylinder misfire counts, long & short term fuel trims, etc.

I heartily propose that you use both data sets as much as possible.
In a perfect world we try to come up with a troubleshooting theory via
what the computer has observed, and then read the plugs & see if
you can get the 2 data sets to agree (cross-correlate) with each other?

When you can make this happen, the parts cannon remains
in storage, and you get the deep satisfaction of successfully fixing with
intent.

I know a favorite phrase is "Analysis Leads to Paralysis"...but a lot of times
this is said by the dudes who are busy chucking their best troubleshooting
info into the trash can while they're saying it. Been there, heard that.
SMH. :0)

****

If you have any questions after all this, fire away. I like spark plugs
as much as Frito likes money...

 

[termite]

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.)

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 --

Thanks Road Trip. I'm fixing to take another look at the plugs later today and will try to grab a couple decent pictures.

I only gave them a quick look yesterday as time was short and several plugs didn't want to come out for me. No idea how long they had been in there but i suspect quite a while. Have heard the suburban sat for a period before I got it which we all know does bad things to improperly prepped equipment.

Nice to see I'm not the only one that takes them out and marks what cylinder they came from! I mark the new one too, right before it gets anti seize on its threads and goes in the hole( gap checked first). I didn't have a chance to look closely at the plugs out of Rawhide (which I'm sure are the original ones) when I changed them, because I had to head out with my friend who's moving, to work at his place. He actually was waiting for me while I changed the last 3 plugs! But I kept them, so they can be looked at later. From what I recall though, they didn't look too bad for 120K.

I don't normally mark them unless I'm looking to learn something from them or want to show them to someone. I've never had a plug out of the box gapped correctly despite counter guys saying "they're pre-gapped for that vehicle". Trust, but verify. My new ones were gapped closer to .060 than .035 out of the box....

 

[HotWheelsBurban]

Thanks Road Trip. I'm fixing to take another look at the plugs later today and will try to grab a couple decent pictures.

I only gave them a quick look yesterday as time was short and several plugs didn't want to come out for me. No idea how long they had been in there but i suspect quite a while. Have heard the suburban sat for a period before I got it which we all know does bad things to improperly prepped equipment.



I don't normally mark them unless I'm looking to learn something from them or want to show them to someone. I've never had a plug out of the box gapped correctly despite counter guys saying "they're pre-gapped for that vehicle". Trust, but verify. My new ones were gapped closer to .060 than .035 out of the box....

Yes I saw too many parts get dropped in my parts store days. And plugs especially, because they would fall out of the box if it wasn't closed right. That was one of my many jobs, to see that boxes were closed!

 

[Road Trip]

Thanks Road Trip. I'm fixing to take another look at the plugs later today and will try to grab a couple decent pictures.

Have heard the suburban sat for a period before I got it which we all know does bad things to improperly prepped equipment.

You just described a perfect example of why 2 otherwise identical 25+ year old trucks
can act so differently -- when you are trying to figure out why one is just worn in &
steady as she goes, while the other is offering up strange & mysterious behavior
when you try to drive it?

From the engine perspective, one big secret is how was it used/not used before you bought it?

At one end of the troubleshooting spectrum, the engine was used every single day
by the PO, who ran his business w/this truck. Let's say that the PO treated like it
was the foundation of his enterprise, never cheated/skimped on preventive maintenance,
either fixed it himself or took it to a trusted mechanic at the very 1st sign of
malfunction, etc.

When you pull a set of plugs out of this vehicle, all 8 look almost always look the same,
and you hear yourself telling the new owner that this engine looks "worn in, not worn
out." Even with a ton of miles on the odo. Always a beautiful thing to see.

On the other end of the troubleshooting spectrum, whenever I hear "sat for a period",
or "My dad / uncle / granddad / neighbor drove this for years, then something went
wrong, and it got parked for many more years under the tree in the backyard."
...and now we've decided to put it back on the road?

You & I both know that in all probability that the troubleshooting of this 'barn find'
will be much more involved, interesting, challenging, frustrating, etc. (gas tank is a
spelunker's delight, every shared ground in the truck has a different resistance
due to corrosion, etc.)

Here's an example that few (normal) people ever consider, but can lead to a
weird motor that runs good...and bad...and then sometimes good again as
you move up the rpm band? (Normally I would get to take a crack at it after
several others had brought their best mojo and no joy.)

Here's a hint. IF I were to fall in love with a pristine (rust free) GMT400 truck
that had been sitting since the financial panic of '08, here is what I would do
if I was going to (try to) fix it up, keep it as 'original as possible',
and drive on that same motor for reals. Before disturbing anything or
stuffing a fresh battery into it, I would pull both valve covers, and
take sharp photos of where the rocker arms have been positioned,
frozen in time, for the past 15+ years.

Why? Because most of the valves are in the fully closed position, so the
associated valve springs have been standing tall at their installed height...
and they are probably still providing reasonably good seat pressure.

I don't care about those. As a troubleshooter, *I* am very interested
in those valves that have been hanging full open for all this time.
(due to cam lobe orientation) 2 reasons come to mind:

* the first is that if it was a hanging open intake, and the air cleaner was off,
then this is the cylinder that has the highest chance of having rusty cylinder
walls / piston rings rusted to the bore, or even critter FOD in it.

* the second is that IF the hanging open valve was an exhaust, then this
is the cylinder that's going to fail for a burnt exhaust valve down the road.

What is going on? The answer is that the springs that have been compressed
to the shortest part of their travel for all these years will have 'taken a set', and
have lost a percentage of their spring pressure!

If you take all 16 of these valves springs off the heads and stand them up side by side,
maybe 12 or 13 will all be the same height (and measure similarly on a valve spring tester)
while the remaining springs will stand shorter/measure weaker.

And, if all this is left inside the engine, you can end up with a motor that
runs alright at low speeds, then as the rpm increases and the spring's resonant
frequency is hit, you get the equivalent of high speed valve float/cylinder misfire
way down in the rpm band where you are trying to cruise down the interstate.

Makes perfect sense in a way. What's unfair is that this same motor will
probably give you reasonably decent compression test results, because
we can't stimulate the fault at slow engine cranking speeds. (!)

****

How did I learn this? Well, 'cuz the only degree that fit into my budget was
the Degree from the School of Hard Knocks. ;0) And while spending endless hours
at the blast cabinet cleaning up the rusty bits I had plenty of time to wonder
why some used cars were so smooth & giving, whereas other used cars
were nothing but a non-stop @$$-kicking. As always, with enough quality
gonkulation time the patterns would emerge from the painful memories. :0)

****

Anyway, you seem to be the type who is going to outlast whatever shenanigans
that your Suburban is going to try to pull on you. I forecast much success,
sooner rather than later.

Cheers --

 

[Road Trip]

Hmmm… yes…. Those appear to be spark plugs…. In a past life they were new, now they aren’t

I haven’t figured out plug reading either, just watched a video of this old man yelling while explaining it “put in fresh plugs and don’t let the engine idle! Make a wide open throttle pass and shut the engine off before it comes back down! Take them out before they cool and you can read them! Here you can see this one is lean!”
He had cut all the threads off and was looking at the entire porcelain piece. They all looked like spark plugs that ran for about 10 minutes to me

Orpedcrow,

Last night I got to share just the tip of the iceberg re: spark plug reading.

Stop the Presses! I have found the All U Can Eat spark plug troubleshooting buffet
that I couldn't find last night...and here is the rest of the iceberg:

First, here is a spark plug color palette, arranged in a
Too Cold/Rich > Good > Too Hot/Lean order:

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(Credit: garage.Grumpysperformance.com)

If you are genuinely interested in where these guys have taken spark plug reading
to a fine art, then forget the yelling dude & instead head down this amazing
rabbit-hole...which happens to have sub-rabbit-holes referenced within.

Make a big bucket of popcorn & descend...eventually you will resurface, eyes glazed
over, and your noggin feeling like an overstuffed washing machine banging out
a polyrhythmic beat. :0)

There really is some great info on the interwebs -- the only problem is finding it.

Enjoy --

 

[Orpedcrow]

@Road Trip thanks for sharing your wealth of knowledge with us plebes

 

[Road Trip]

@Road Trip thanks for sharing your wealth of knowledge with us plebes

My pleasure. My favorite people to hang out with are those who'd rather build it themselves
...and own it, rather than buying it and then stressing about paying it off over the
next 72/84+ months.

I was fortunate that I had a series of seemingly omniscient mentors over my career.
After one gentleman showed me a troubleshooting trick that he had spent several years
perfecting, he said, "That info is not yours to keep...it is yours to pass along whenever
you have the chance."

I had/have great respect for that mentor. Therefore, I am doing nothing more than what
he asked me to do. (!) And I think the modern idiom of what he told me is simply
"Pay it Forward."

Thanks for the positive feedback. Again, my pleasure.

 

[termite]

he said, "That info is not yours to keep...it is yours to pass along whenever
you have the chance."

That's one of the best attitudes to have regarding knowledge and experience. To echo Orpedcrow, thanks for passing along the info and rabbit hole to slide into it.

Once my wife gets home and takes over kid detail for a few minutes, I'm going to try to grab a few decent pictures of all 8 plugs laid out together. If i can manage some decent lighting.

 

[Road Trip]

Once my wife gets home and takes over kid detail for a few minutes, I'm going to try to grab a few decent pictures of all 8 plugs laid out together. If i can manage some decent lighting.

The closer you can get to full spectrum light (sunlight) the better. Standard
incandescent bulbs put a warm tint on the subject matter. Fluorescent lights
put a bluish tinge. Early versions of (partial spectrum) LEDs also goof it up
for us guys on this side of the screen.

Full spectrum lights like these work pretty good, especially if you're careful
not have some plugs in direct light, with the others in shadows. (I've seen
every variation of this.) Believe it or not, the camera (phone?) flash is hit
or miss.

Seriously, indirect sunlight seems to work well, with the full spectrum LEDs
a close second. I know this seems fussy, but unless we're working with
a gross failure, it's all about the shading.

Then again, since these plugs were installed by the PO w/unknown variables,
we can relax our standards a bit & just go with what you have on hand.

No hurries of course...