Cylinder #7 down on compression
what o you see in #5 plug? What causes the electrode post to get discolored? I'm off today and I'm going to give a leak down test a try. Will post what I find later.
I was taught to look at every spark plug I took out, instructed that
you could tell an awful lot about an engines running condition, and lotsa other stuff, like valve guides failing, ring failure, detonation, intake gasket leak, bent pushrod, worn cam lobe, timing, - all in a glance.
I was taught to look for a difference, then figure out why.
Your #5 plug is different, from all others, yet #7 is low compression.
My conclusion is #5 plug came outta #7 cyl, and got mixed up, previous to you knowing the importance of order, - or got exchanged at an earlier time.
Just experience and work habit .
Still needs to come apart, regardless.
Good luck, you'll be okay, lottsa help here.
PS. #5 plug looks kinda wet, and seems to have an irregulaty/protrusion toward the center porcelain, might just be the pic.
Is there something goofy there ?
The center electrode is discolored by contaminants, (oil sucked up), incomplete combustion, ( low compression), etc