Spark Plug conditions?
Thread Starter
Intermediate
Joined: Oct 2001
Posts: 28
Likes: 0
From: North Branch Mn
Spark Plug conditions?
I just pulled my plugs out. I noticed that some of them were nice, dry and clean. Others had a white chalk coating, and others were wet and had oil caked on them. My engine rebuild (and these plugs) only have 15K miles on them. What causes this? What could be wrong?
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Re: Spark Plug conditions? (Jason - 85)
On the ones that look like they're soaked with oil, what do the threads look like? Rust indicates coolant; ie, a bad head gasket. If they smell like gas, could be a rich or leaking injector. Check fuel pressure. White is indicative that those cylinders are running lean. What appears to be happening is that the rich (or oil soaked appearing plugs/cylinders) is causing the O2 sensor to read a rich condition, which in turn is causing the ECM to narrow (lean) injector pulse width. This would be particularly true if the oil soaked plugs came out of the left head; ie, closest to the O2 sensor. A scan tool would show this. You can also check by grounding the diagnostic connector with the engine running and in closed loop. If the Check Engine Light is on more than it's off, you're running rich. However, it's probably better to check compression while the plugs are out or to run a leak down test as you may have rings that never sealed following the rebuild.
