How to read spark plugs - Tuner-Junction

njn63 · #1 (**permalink**) April 2nd, 2006, 05:52 PM

This is kind of a lost thing on our generation from what i've seen. You can tell a lot about what is going on inside a motor by the plugs.

http://www.densoiridium.com/howtoreadusedplugs.php

Quote:

Normal- Light grey or tan deposits and slight electrode erosion

Carbon Fouling- Dry, soft black carbon on the insulator and electrodes.
Symptoms: Poor starting, Misfiring, Faulty acceleration
Causes: Faulty choke - over rich air/fuel mixture, Delayed ignition timing, Bad ignition leads, Plug heat range too cold

Pre-Ignition- A melted or burned center and/or ground electrode, blistered insulator and aluminum or other metallic deposits on the insulator
Symptoms: Loss of power causing engine damage, Pre-ignition occurs when combustion begins before the timed spark occurs.
Causes: Plug insufficiently tightened, Engine insufficiently cooled, Ignition timing too advanced, Plug heat range too hot

Over Heating - An extremely white insulator with small black deposits and premature electrode erosion.
Symptoms: Loss of power at high-speed or during heavy load
Causes: Plug insufficiently tightened, Engine insufficiently cooled, Ignition timing too advanced, Plug heat range too hot

Mechanical Damage- Bent electrode and a broken insulator, dents often present on electrode
Symptoms: Misfiring
Causes: Plug nose is too long for engine head, Foreign object (bolt/nut) in combustion chamber

Oil Fouling- Wet, oily black deposits on the insulator and electrodes
Symptoms: Poor starting, Misfiring
Causes: Wrong piston rings, cylinders, and valve guides, Fuel mixture oil content too high (two-stroke engines)

Broken Insulator- Insulator is cracked or split
Symptoms: Misfiring
Causes: Severe detonation, Incorrect tool/torque applied during installation or removal, Careless gap setting

Torched Seat- Melted in the thread and seat area of the plug housing
Symptoms: Loss of power causing engine damage
Causes: Plug insufficiently tightened

carboncivic · #2 (**permalink**) April 3rd, 2006, 08:51 PM

Good info Nick, this is very important info for all home mechanics to know whether the car being worked on.

jon ROCKS!!!! · #3 (**permalink**) April 4th, 2006, 05:01 AM

why dont those jerks say anything about carbon tracking?

A_White_Gs-R · #4 (**permalink**) April 6th, 2006, 10:18 AM

my plugs look like the ones in the overly rich condition yet my problem is im running lean. unless when i altered the fpr to 50psi since im running stock injectors on my gsr its now slightly rich. dont know.

Clone · #5 (**permalink**) April 27th, 2006, 10:48 AM

nice thread, more people should see this... of course, you can find the same thing in the back of every haynes manual...

great info.

EyelessCRX · #6 (**permalink**) June 26th, 2006, 10:51 PM

Great post man! I just checked mine recently and all that I can really see is a little bit of oil on the plug hardly noticable.