What is a "Glazed" spark plug?
#1
11-15-2015, 09:16 PM
What is a "Glazed" spark plug?
Some of you may remember me mentioning "glazed" spark plugs during some troubleshooting some rough running issues in some recent threads. I want to show you what a "glazed" spark plug looks like and describe the tell-tell signs that you have a "glazed" spark plug (or several in my case).
If you are experience a hesitation or slight to moderate shutter on acceleration or when applying a little bit of throttle at cruising speed, you may have one or more "glazed" spark plugs. If you have recently had an exhaust leak around the O2 sensors or replaced a defective O2 sensor, you could have a "glazed" spark plug on that cylinder bank serviced by said exhaust or O2 sensor. Both times I have had issues with the hesitation and shutter on acceleration have been associated with a defective O2 sensor and, just recently, an exhaust leak (flex joint).
Here's what a "glazed" spark plug looks like. (click the two links below) See the little tiny beads of what looks like welding spatter on the electrode and insulating ceramic part around it? THAT is a sure sign that the spark plug has been heated up due to messed up fuel/air inputs to those cylinders. That coating is conductive so some of the electricity sent down the electrode that is supposed to jump the gap at then end, creating a spark, is simply channeled though the conductive coating straight to ground, reducing the size and effectiveness of the spark. Basically a weakened spark. When adding fuel to a cylinder for acceleration, the weakened spark is not able to effectively ignite the mix fast enough. This causes a misfire of sorts.
[img=http://s20.postimg.org/5dqcqn1bt/Glazed_Plug_1.jpg]
[img=http://s20.postimg.org/dupv1k60p/Glazed_Plug_2.jpg]
On this most recent episode, all 4 plugs on the Bank 2 side (driver's side) of the engine (4.2 A8L engine code AUX) were glazed. I replaced all of the spark plugs yesterday and drove the car today with NO hesitations or shuttering on acceleration.
The first time this happened to me, I spent almost $400 throwing freekin parts at it (fuel pump and associated parts) before it hit me that I had experienced the same thing in the old 87 5000S Quattro about 10 years before. It was behaving the same way but I had pulled the plugs out and noticed that 2 or 3 of them looked "different" than the rest. I went and got 5 new Bosch Platinums for it and it cleared right up.
So, if you're car is hesitating or shuttering a little bit on acceleration, the first thing you need to do before dropping more money than you need to, pull the spark plugs and check'em out. A set of plugs is a hell of lot cheaper than most other items that would cause this same issue.
If you are experience a hesitation or slight to moderate shutter on acceleration or when applying a little bit of throttle at cruising speed, you may have one or more "glazed" spark plugs. If you have recently had an exhaust leak around the O2 sensors or replaced a defective O2 sensor, you could have a "glazed" spark plug on that cylinder bank serviced by said exhaust or O2 sensor. Both times I have had issues with the hesitation and shutter on acceleration have been associated with a defective O2 sensor and, just recently, an exhaust leak (flex joint).
Here's what a "glazed" spark plug looks like. (click the two links below) See the little tiny beads of what looks like welding spatter on the electrode and insulating ceramic part around it? THAT is a sure sign that the spark plug has been heated up due to messed up fuel/air inputs to those cylinders. That coating is conductive so some of the electricity sent down the electrode that is supposed to jump the gap at then end, creating a spark, is simply channeled though the conductive coating straight to ground, reducing the size and effectiveness of the spark. Basically a weakened spark. When adding fuel to a cylinder for acceleration, the weakened spark is not able to effectively ignite the mix fast enough. This causes a misfire of sorts.
[img=http://s20.postimg.org/5dqcqn1bt/Glazed_Plug_1.jpg]
[img=http://s20.postimg.org/dupv1k60p/Glazed_Plug_2.jpg]
On this most recent episode, all 4 plugs on the Bank 2 side (driver's side) of the engine (4.2 A8L engine code AUX) were glazed. I replaced all of the spark plugs yesterday and drove the car today with NO hesitations or shuttering on acceleration.
The first time this happened to me, I spent almost $400 throwing freekin parts at it (fuel pump and associated parts) before it hit me that I had experienced the same thing in the old 87 5000S Quattro about 10 years before. It was behaving the same way but I had pulled the plugs out and noticed that 2 or 3 of them looked "different" than the rest. I went and got 5 new Bosch Platinums for it and it cleared right up.
So, if you're car is hesitating or shuttering a little bit on acceleration, the first thing you need to do before dropping more money than you need to, pull the spark plugs and check'em out. A set of plugs is a hell of lot cheaper than most other items that would cause this same issue.
Last edited by dave944; 11-21-2015 at 04:27 PM.