Fouled worn spark plugs (1 Viewer)

[Kernal]

Recently picked up a neglected 95 FZJ80 and have been going through the PM one area at a time.

So just pulled the leaky valve cover to replace the gasket, found it to be cracked and shrunken as expected. Spark plug tube seals, ditto, cracked and leaking, oil in most of the tubes.

Removed the spark plugs using a GearWrench 5/8" socket with attached wobble extension, #80546 (heat control valve and hoses already removed). One plug was a bit loose, one had resistance all the way out.

Here's a few photos; look like they've been in there way too long along with some oil fouling, got a one time misfire in #6 and that plug (far right) is a bit cleaner than the rest, but it doesn't look steam cleaned. Distributor cap and rotor were also very worn, they've been replaced. Yazaki spark plug wires marked 2003.

(#1-#6 left to right: click on the photos and magnify for a close-up view)

Note the significant build-up of deposits on the side electrodes, except #1 and #6 (cleanest).

 

[1911garand]

I recently did a tune-up as well, very similar plugs. Ran great before tune-up, even better now.

 

[Michael Hanson]

Hi, While these trucks are not speed rockets,it amazes me that people don’t do simple maintaince on the trucks. Yes they are slow when you don’t maintain them. Mike

 

[musthave]

I'm not surprised that it was still running, perhaps a testament to the fine craftsmanship. It's ashame to see things like this though. Plugs are cheap & easy.

 

[Kernal]

The 80 I'm working on (plugs at top of thread) was running OK even with the fouled plugs, felt maybe a bit less power than my other 80 that's up to date with it's PM. I am concerned about the fouling, the valve stem seals likely need replacing.

 

[77mustard40]

Just changed mine last week along with plug wires and tube seals and though mine were in bad shape. Plugs were gapped way to wide and had some carbon buildup, runs night and day better. But mine didn’t look nearly as dirty so I consider myself lucky.

 

[BILT4ME]

Those look to be original plugs.

There is some oil fouling and some fuel fouling, but the gap is so huge, I would discount what I see there as a "diagnosis".

I would bet the valve seals are toast as well, but how deep do you want to dive?

The gunk on the threads on #4 is from the bad plug tube seals and the oil getting cooked on the threads as well as oil from the cylinder firing.

Use a good clean old plug and some solvent and oil (PB Blaster would work well) to loosen the gunk and run the plug in and out numerous times to clean the threads. Do NOT use a cutting type tool to clean those threads.

Whatever you spray in WILL end up in the cylinder, so go sparingly and let it soak in between.

 

[Kernal]

IIRC #3 came out easiest, #4 came out with most resistance, which fits with the comments. My guess is the plugs have been in at least 10 years and 100,000 miles, that's how long the PO owned this 80, possibly longer.

The original owner (before 2010) may have replaced the head and head gasket as the head is missing the VIN # plate that the original heads come with. That might have been in 2003 (date of the spark plug wires and ?? the spark plugs).

 

[jaymar]

Spark plug THREAD question: what's the spec on the holes they screw into? Need to get compression and leakdown testers, have to make sure the supplied hoses will fit. I see different kits specifying 10mm 12mm 14mm 16mm 18mm. Some of them don't even give a thread pitch; that's all they say. What do I need here? Thanks!

 

[BILT4ME]

Spark plug THREAD question: what's the spec on the holes they screw into? Need to get compression and leakdown testers, have to make sure the supplied hoses will fit. I see different kits specifying 10mm 12mm 14mm 16mm 18mm. Some of them don't even give a thread pitch; that's all they say. What do I need here? Thanks!

Most compression testing kits come with adapters to fit the common spark plug hole sizes. If not, don't buy it.
The following link states sizes and at the end advised that 14mm and 18mm are the most common newer sizes.

I believe the LC uses 14mm.

Spark Plug Threads Sizes Table

Spark Plug Threads Sizes and Tapped Hole - The SAE Standard includes the following sizes: 7⁄8- inch nominal diameter with 18 threads per inch:

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