View Full Version : spark plugs....what could this mean?


rutwad
03/15/06, 08:38 PM
I pulled the plugs from my bronco with less than 500 miles on them. Some are oily black and others are tan. What could make them so different?

raharr3
03/15/06, 08:41 PM
Are they on opposite heads? ( the oily vs the tan ones)

bigulcer1
03/15/06, 08:42 PM
Running to rich,maybe.

rutwad
03/15/06, 08:53 PM
no, not on opposite heads. That is what really confused me. I pulled one that was tan, then the one right next to it was black and had oil on the threads.

I thought about it being too rich, but what about the tan plugs. They seem to have the right mixture, maybe even slightly lean. If the motor was rich, wouldn't it run rich on all cylinders?

2badrotties
03/15/06, 09:03 PM
Truth is ... color on plugs doesn't mean what it used to. Back in the day with leaded fuel color meant something but unleaded fuel doesn't do that. If they are tan is is most likely rich. It is not unusual to have uneven cylinders on a small block ford but usually it is the end cylinders that run lean. If you have what seems to be a rich condition but don't think it should be, check your wires , cap, and ignition system. Maybe the plugs are not firing fully. When people look at plugs for readings they use something they can see with and check down around the bottom of the insulator not so much the tip.

Check to see is you have really good spark and go from there. Oil around the threads is probably leaky valve cover gasket ... maybe :)

bigulcer1
03/15/06, 09:05 PM
Have you treid the timing or your points in dist.

rutwad
03/15/06, 09:14 PM
Well, at least you guys have given me some more things to look for. Leaking valve covers, points, timing, etc.

thanks

Pa PITT
03/15/06, 09:23 PM
Give Us A Few More Details ...like How Many Mile On The Motor
How Fresh Is It ...if It Like Mine And I Crank It 30 Times And Dont Get It Out Of The Shop ..well Then That Gives A Different Reading Than
One Of The Guys Who Drives 20 Miles A Day At Hyw Speed ....
If It's Not Fresh Or Has Set For The Last 2 Years It May Be The Valve Stem Seals ..i've Had More Trouble With Them Than Anything ...
Also Spark In The Old Stock Dis..as To One With A Boost To It ...i Was Impressed At How The Pretronx My Buddie Put On His ....
Pa Pitt...

j.r.nice
03/15/06, 10:34 PM
I pulled the plugs from my bronco with less than 500 miles on them. Some are oily black and others are tan. What could make them so different?

If it's oily, probably valve seals

yellow66
03/15/06, 11:20 PM
You stated oil on the threads? Or do you mean oil on the electrode of the plug. If you have oil on the electrode of the plug then you have a valve seal or ring problem. As for the tan colored plug that is normal. If you just have oil on the threads you could have a leaking valve cover gasket. Good luck.

2badrotties
03/16/06, 12:17 AM
Back on his 2nd reply he said ... " then the one right next to it was black and had oil on the threads " so I was figuring leaky valve cover gasket but maybe not :)

rutwad
03/16/06, 01:38 PM
The PO said the motor (351w bored .030, cammed, Holley pro jection kit) was rebuilt 3500 miles ago. It was already rebuilt when he bought it and he owned it for at least 3 years, so it wasn't driven much. I have owned it for 3 months and put new plugs in when I bought it. The last 75-80 miles were all highway. It was at a local shop for 2-3 weeks where it was cranked up just to pull it inside at night, and back out during the day. So it has highway mileage, and shop "crankage". I have probably cranked it several times around the house and never gone over 3 miles, but again the last 80 miles were driven the day I pulled the plugs.

The electodes looked smutty black like it may have been rich, but they did not look wet. Actually the threads on 2 of the plugs were wet with oil, not soaking wet but enough I could wipe some off with my fingers.

airman
03/16/06, 01:57 PM
Are they on opposite heads? ( the oily vs the tan ones)

By opposite, I think he meant opposite in the firing order not opposed cylinders.

BUCKETOBOLTS
03/16/06, 02:59 PM
My bet is on valve stem seals. I'd pull the valve cover to take a peek and see what is in side. Replacing them isn't hard just a little time consuming.