98 yukon, Oil on cylinder #1 Spark plug..?

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

OilBurner2003

Full Access Member
Joined
Jul 24, 2022
Posts
280
Reaction score
170
Bet you guy's thought you saw the last of me, huh? Been working on a mercury cougar for the past month! Anyway, Took the truck on a drive, noticed it was missing slightly on cylinder #1. Wasn't too worried, turns out the plug is a different model than the 7 Others. Previous mechanic must have gotten one mixed up somehow. However...There is Oil on the beginning of the threads, but the rest of it looks decent. Honestly, I'm wondering if someone spilled oil off the valve cover and it made it's away down there. The end of the spark plug looks decent, I'm not even sure how oil could be in the combustion chamber to that amount and not destroy the plug, much less how it would get there without me noticing a major issue. I'm gonna replace the plug with the correct model and monitor it, maybe it's just a random occurrence. Just wanted your guy's opinions. Thanks!
 

OR VietVet

Multnomah Falls
Supporting Member
Military
Joined
Oct 8, 2014
Posts
20,515
Reaction score
35,891
Location
Willamette Valley
Please post a pic of that plug from several angles. Usually when a previous owner does that, it means an oil fouled plug that he/she changed out to allow for a smooth run engine for a sale.
 
OP
OP
O

OilBurner2003

Full Access Member
Joined
Jul 24, 2022
Posts
280
Reaction score
170
Please post a pic of that plug from several angles. Usually when a previous owner does that, it means an oil fouled plug that he/she changed out to allow for a smooth run engine
Unfortunately, I did not take a picture. I was just wondering what a main cause could possibly be.
 

B-train

Full Access Member
Joined
Sep 12, 2022
Posts
2,207
Reaction score
3,793
Bet you guy's thought you saw the last of me, huh? Been working on a mercury cougar for the past month! Anyway, Took the truck on a drive, noticed it was missing slightly on cylinder #1. Wasn't too worried, turns out the plug is a different model than the 7 Others. Previous mechanic must have gotten one mixed up somehow. However...There is Oil on the beginning of the threads, but the rest of it looks decent. Honestly, I'm wondering if someone spilled oil off the valve cover and it made it's away down there. The end of the spark plug looks decent, I'm not even sure how oil could be in the combustion chamber to that amount and not destroy the plug, much less how it would get there without me noticing a major issue. I'm gonna replace the plug with the correct model and monitor it, maybe it's just a random occurrence. Just wanted your guy's opinions. Thanks!
You are probably seeing what sticks down into the head and has reside from poor combustion. If you have a miss on #1, you probably have a bad spider tube and poppet.

Unless the plug was failed or disconnected, I don't see many other options
 
OP
OP
O

OilBurner2003

Full Access Member
Joined
Jul 24, 2022
Posts
280
Reaction score
170
You are probably seeing what sticks down into the head and has reside from poor combustion. If you have a miss on #1, you probably have a bad spider tube and poppet.

Unless the plug was failed or disconnected, I don't see many other options
All injectors are brand new. Knowing this old engine, it's probably something OR mentioned. Will be doing some tests tomorrow.
 

OR VietVet

Multnomah Falls
Supporting Member
Military
Joined
Oct 8, 2014
Posts
20,515
Reaction score
35,891
Location
Willamette Valley
Run a compression test on that cylinder and the cylinder(s) next to it but make sure all plugs are out during any compression test.
 

Forum statistics

Threads
131,754
Posts
1,856,270
Members
96,017
Latest member
CountryRoads
Top