So I pulled my plugs today and this is what I found

I'm a bit confused by this, never having seen it before. Some of the plugs had heavier deposits, but all this reddish-brown color. Could someone please enlighten me as to the source / cause?

1995 F150 XLT extended cab 300 l6

 

Keep the plugs organized so you can tell which cylinder each one came from. If you can't find the right Haynes for your truck (read this caption):

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...go to a local parts store and look at the inside back cover of ANY Haynes. It has a full-color & more-thorough version of this:

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The best replacement plugs are common, inexpensive AutoLite Copper resistors. These old engines don't run as well on expensive high-tech unobtanium spark plugs.

Reddish deposits are either gasoline varnish (from old or low-quality gas in the tanks, &/or infrequent filter changes), or from blowby sludge coming through the PCV into the intake, or from rust/dirt passing through the air filter.

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If you want to change the fuel filter, read this caption to make sure you get the one with long nipples:

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Before attempting to disconnect the fuel lines, read this:

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Your signature is better than most, but there's a lot of info missing:

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Additives in your gas used to suppress detonation..

 

I appreciate both of your responses, and thank you especially Steve for the in-depth look at my issue.

Raski I believe you may have hit the proverbial nail straight on the flat part on top... I just pulled the plugs while I was in there retarding my timing by a couple of degrees... Turns out it was sitting at 11.5 or 12 btdc. I had been using octane booster to try and stop the terrible bacon noises coming from my motor. Turns out it was just advanced too far 🤪