Spark plug reading - lots of variance

[mathlete]

Spark plugs and NGK wires had ~40k miles on them. Truck is at 252k. No codes being thrown. No significant symptoms other than occasional pulsating/oscillating idle between 580-600 RPM. This does not happen very often, though.

This is the first time I've pulled and inspected them in my ownership. Could use some help reading these. Here are the first 3 in order.

PLUG 1

PLUG 2

PLUG 3

 

[mathlete]

PLUG 4

PLUG 5

PLUG 6

 

[mathlete]

Plugs #1 and #2 seem to be similar and mostly normal apart from the rough looking ground electrode.

Plugs #3 and #6 seem to be similar - they have more carbon buildup at the end of the threads towards the electrode.

Plug #4 has some gunk and oil in the tube. Not substantial, but enough to buy spark plug seals and a valve cover gasket. Planning on installing those.

Plug #5 was the only one that was "wet" on the electrode. I did a sniff test and I'm leaning towards a gas smell over an oil smell. I could be wrong.

I've installed new plugs and plan on running it 500 miles and rechecking.

Other than spark plug seals to fix #4, is there anything I should look into in the meantime? I'm doing a number of maintenance items currently - plugs, oem wires, air/fuel filters, pcv valve, distributor cap/rotor/o-ring, and trying to replace old vacuum/coolant hoses as I spot them.

 

[Kernal]

How much oil does the engine consume?

What type of driving do you do, short distance, low speed, or long highway trips?

The RPMS at idle, if correct (580-600) are too low (check for a vacuum leak, cracked air/vacuum hose top of engine, intake hose, etc).
Got any large oil leaks (Valve cover)?

Already mentioned: replace the Valve cover gasket and spark plug tube seals, clean baffle inside valve cover while it's off.
Distributor O-ring, PCV hose and gromment, breather hose, clean throttle body well (off the vehicle is best), replace Throttle Body gasket
OEM plug wires, Air filter, oil filter, etc

If you do remove the Throttle Body plan to replace the two coolant hoses one in front, one below.
you'll also need a section of Fuel hose for the short ~4-5" vapor line coming off the TB.
And a new O-ring for the IAC valve which should be cleaned while it's off the engine.

If your cables (Throttle/Kickdown, Cruiser Control, or Accelerator) have peeling rubber now might be a good time
to slide some 3M dual wall flexible adhesive lined heat shrink tubing (~3-1 ratio) over the cables then shrinking them down
using a heat gun. Start at one end and work slowing forward/circumferentially as it shrinks down

Reseal the front half "moons" while the valve cover is off, doesn't take much sealant ( FIPG, Triple Bond, Hondabond, take your pick)

Rewrap the engine harness especially around the EGR pipe then add a ~ 5-6" section of a heat protective sleeve (split velcro type) over
the harness closest to the EGR pipe.

While the valve cover is off is also a good time to replace the Heat Control valve if it's old or the original. Ditto for
any of the how water (heater) hoses close to the firewall. 5/8" for the front circuit, 1/2" for the rear. Use OEM
or Gates Green Stripe hoses, everything else is crap.

Tt's also a good time to replace the PHH and PHH pipe.

Get a cheapo scan tool that can do some basic live data ie: TPS %, engine coolant temp, etc.

FWIW/IME Iridium plugs (Denso Iridium TT for example) last longer than stock type.

 

[robnicko]

while you have the valve cover off check your valve clearances are in spec, both intake & exhaust

 

[mathlete]

Engine consumes about 1qt every 2000-3000 miles. Mostly highway miles. I know I've got a sizable upper oil pan leak and possible rear main seal leak. Not dripping onto the garage floor...yet. Valve cover seems leak free. The PCV valve area is a bit of a mess, which is why I'm replacing that.

I'm replacing the intake tube and HCV - got those parts already. The PO took care of the PHH and rear heater delete, but I should double check those now that I'm thinking about it.

I'll check valve clearance next week when I take the valve cover off. Still waiting on spark plug gaskets to arrive.

Hopefully when I've gone through everything mentioned I'll see some improvement in my idle situation and how the plugs look.

 

[baldilocks]

With 252k miles and no peculiarities about how it runs I wouldn’t be concerned about those plugs. They look pretty good to me. You might pull the injectors and have them checked out just because.

 

[Brav]

Another vote to get injectors cleaned and flow matched. Made a big difference. Had two that were way off.

 

[mathlete]

I've ended up giving myself quite a bit to do - "while you're in there", as they say. Working on refreshing the entire cooling system and replacing all vacuum lines. Gonna pull the injectors as well. Got the throttle body cleaned up this weekend - blew out and cleaned all passages, also cleaned the IAC valve with electric parts cleaner. It was caked in gunk.

I noticed a bit of play in the throttle lever thing before the plate opens. Is this normal? See the video below:



Also, I've gathered all vacuum hose except for 90910-05217 and 90910-05212. These are hoses under the upper intake. Local dealer is telling me "nationwide backorder". I ordered them over 3 weeks ago. Anyone know the story on these hoses? Can't seem to get any info

 

[jpoole]

"1qt every 2000-3000"

In my opinion this is high and based on the spark plugs (the buildup on the first few looks like carbonized oil buildup to me) and lack of oil making it to the ground I think it's likely losing this oil into the combustion chambers. Most of your oil consumption is probably coming from the valve stem seals if they haven't been replaced.

I don't think this is unique but for reference my '97 with about 330k miles on the original engine it never needs oil between changes (which I do around 6k or 7k mile intervals) and the oil level doesn't noticeably move on the dipstick. I replaced the valve stem seals on this engine around 100k miles and 10 years ago. There are a few small leaks and drips do make it to the ground where it's parked occasionally.

You can lose/eat oil from other sources like rings, etc. but that's a lot less common on these.