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

[OilBurner2003]

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]

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.

 

[OilBurner2003]

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.

 

[OR VietVet]

Valve seals, piston oil rings, valve guides......

 

[OilBurner2003]

Valve seals, piston oil rings, valve guides......

Hm. All stuff I was thinking about too. Thank you for the information sir!

 

[B-train]

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

 

[OilBurner2003]

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]

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.

 

[OilBurner2003]

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.

Will go get a kit.

 

[OR VietVet]

Just remember that you can have good compression and still get an oil fouled plug.

 

[Eman85]

Right below the oil fill tube, buy a matching plug and clean the area good.

 

[OilBurner2003]

Just remember that you can have good compression and still get an oil fouled plug.

I have a symptom I've never seen before. Very rough idle with some misfires, as soon as you get over 40 MPH all misfires go away...? I swear, this truck throws everything under the sun at me. May be making a call to previous Mechanic.

 

[OilBurner2003]

Right below the oil fill tube, buy a matching plug and clean the area good.

Pulled the plug today, that's actually exactly what I did. Had oil on it. Didn't have time for a compression test, but I'm sure there's something along the lines of either a valve or something else. Will see if I can do it in the morning.

 

[OR VietVet]

I have a symptom I've never seen before. Very rough idle with some misfires, as soon as you get over 40 MPH all misfires go away...? I swear, this truck throws everything under the sun at me. May be making a call to previous Mechanic.

Sometimes, when you have misfires that seem to go away at higher rpm's, there is a vacuum leak or a fuel feed problem.

 

[OilBurner2003]

Sometimes, when you have misfires that seem to go away at higher rpm's, there is a vacuum leak or a fuel feed problem.

Even though the Injectors and DELPHI Pump are brand new, I've always wondered at this point if I should put a FP gauge while driving. It's supposed to be above 55 PSI or close to it, correct?

 

[OR VietVet]

Yes, but what is the readings at idle and slight throttle, that I assume is where your misfires are happening, correct?

 

[OilBurner2003]

Yes, but what is the readings at idle and slight throttle, that I assume is where your misfires are happening, correct?

Last I checked, FP was 55 at idle, I believe slight throttle was maybe 54/55. I should hook up the gauge again and see what it give's me now.