HOW TO: read used plugs

[trinydex]

http://densoiridium.com/howtoreadusedplugs.php

Reading a Spark Plug

NASCAR engine tuners love spark plugs they can "read". The discoloration on the insulator after a few laps helps them understand how the electrical elements of the engine are performing.Â*

Â*
Not all plugs allow you to "read" them. The corona, a brown deposit on the insulator, is the glow that appears above the spark plug housing around the base of the insulator. The appearance of a corona is not detrimental to the operation of the spark plug. Contrary to common belief, this condition is caused by electrical stress in the air adjacent to the insulator. Often, the corona stain is mistaken for spark plug gas leakage, but again, this does not affect spark plug performance.

The insulator is ceramic and can be broken, although this is a rare occurrence. Typically, the most common ways the insulator becomes cracked is when the installation is done at the wrong angle, the incorrect torque is used or the removal is forced. (See Installation Guide)

Our primary concern is that you use the appropriate tools and torque during installation. When the insulator is cracked during installation, this can cause a short circuit which will result in irregular idling and misfires during acceleration. (See Common Engine Problems)


Diagnosis of a Used Spark Plug

If you're seeing any of the following, you probably don't have the manufacturer's recommended spark plug installed. But the symptoms are separate from the causes and all the components in an ignition system, no matter how small, will leave some signs on the spark plugs over time if they're not in harmony. This guide can provide insight to the engine's performance.Â* Â*

Normal
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Light grey or tan deposits and slight electrode erosion


Carbon Fouling
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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



Â* Pre-Ignition
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http://www.socalevo.net/gallery/albums/userpics/10991/dia_preignition.jpg


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



Â* Over Heating
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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



Â* Mechanical Damage
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http://www.socalevo.net/gallery/albums/userpics/10991/dia_mechanicaldamage.jpg


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



Â* Oil Fouling
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http://www.socalevo.net/gallery/albums/userpics/10991/dia_oilfouling.jpg


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)



Â* Broken Insulator
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http://www.socalevo.net/gallery/albums/userpics/10991/dia_brokeninsulator.jpg


Insulator is cracked or split

Symptoms:
Misfiring

Causes:
Severe detonation
Incorrect tool/torque applied during installation or removal
Careless gap setting



Â* Torched Seat
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http://www.socalevo.net/gallery/albums/userpics/10991/dia_torchedseat.jpg


Melted in the thread and seat area of the plug housing

Symptoms:
Loss of power causing engine damage

Causes:
Plug insufficiently tightened

[alan678]

Can someone read this one for me...its between normal and overheating from what i can see...but i am not a pro...

Thanks

http://i77.photobucket.com/albums/j52/alan_678/P9102451.jpg

[trinydex]

did you remove the plugs right after a pull?

[alan678]

no...those are after a whole night of cooling down...and 2 miles of casual driving before i parked it...

[trinydex]

yeah you need to pull plugs right after there's a problem otherwise you just get a confused reading or like... it normalizes a bit and you can't tell anything.

[alan678]

ok...sweet...thanks for the tip...will do tomorrow...

[nothere]

I've done wot plug reads on my old cars. Shut off the key and brake down to a stop. You really need a lighted magnifying viewer (like what the doc uses to see the wax in your ears). What you are looking for is a small graduation of difference from the perfect plug.

With a turbo you are at a disadvantage. No one should be cutting their car off after an extended wot at the instant they let off the pedal. If you let the turbo cool off by idling, by the time the turbo is cool the plugs are long cleaned/changed by the idle.

[nothere]

for the hardcore, and some good points


The Air/Fuel Map
Look at the porcelain and divide it into 3 areas, top, middle and bottom in about 1/3rds.

Top Area: This area is your idle circuit and for the racer real has very little meaning. However if your car is a street driven vehicle then we need to attempt to get this portion to a dark gray color by tuning the AFR, Idle Air Bleeds and the four corner Idle adjustments until we get a clean crisp idle and total combustion of the fuel at idle. Keep in mind that the idle circuits are totally isolated from the rest of the carburetor and can be tuned with very minimal affect on the WOT position A/F Ratio.

Center Area: This is the area that will show the combustion chamber condition at part throttle or cruise with the power valve and secondary venturi's closed. Usually about 30-50 MPH depending on the gear and weight of the car.

Bottom Area: This is where the racer needs to concentrate all his efforts, using a 5x or 10x scope you need to look right down to the bottom of the porcelain where it meets the metal housing of the plug. This is the area that will leave the color that you need to study and tune to. The other 2/3rds of the porcelain will be burned clean by the high heat generated by WOT and high RPM, this is not the time to read for cruise or Idle characteristics.

We're looking for a colored ring right at the base of that porcelain which I refer to as a Fuel Ring. The color will vary depending on the type of fuel your burning, Unleaded Pump gas will leave very little color because of all the additives such as injector cleaners and methanol. Most of us run a 108 or 110 in our bracket cars and these fuels will leave a tan color while the C17 and higher octane fuels will leave an almost gray fuel ring. If you study the ring you will see that it starts to show color just below the base of the ground strap, this is caused by the shielding affect of the strap leaving that portion cooler thus showing the most color. The ring will develop from each side and form a full circle of correct color as you get closer and closer to the correct tune up. If you look down into the bottom of the porcelain and you detect a thin oily deposit you are seeing oil from the combustion chamber caused by either worn or improperly seated rings, you may also detect this with a new engine that hasn't fully seated the rings yet, just don't confuse this with the "Fuel Ring".

Plug Characteristics

Shiny or Glazed Porcelain: This occurs for two reasons, excessive idling or rich idle condition leaving heavy soot deposits. These deposits will burn and create excessive porcelain temps causing the glass to melt usually resulting in a down track popping through the exhaust..
You will usually see splotchy deposits on the plugs after the run, either green or yellow in color and of course the tell tale shiny glaze. The porcelain should have a chalky or dull finish.


Base of threads sooty: This is usually a indication of the plug not being tight enough allowing it allow air to pulled in to the chamber and fuel being pushed out, change the plug, tighten to spec. This area should have a nice dark to medium gray color without heavy deposits.

Black or brown specs: This is an indication of detonation usually caused by too hot of a plug, drop one or two heat ranges and it should go away. The plug gets so hot that it will start to detonate the fuel before the ignition fires, this cause a double flame front and reduces the efficiency of the combustion process as these two flame fronts battle each other in the combustion chamber. The black spots are the result of the fuel deposits being burned onto the porcelain by the double flame front. Once you cool down the plug and remove the secondary ignition source you can re-set your timing to produce the correct combustion chamber temp for optimum power.

I've heard 100's of so called tuners and engine builders tell people that this is normal and nothing to worry about......WRONG. Do not underestimate the damage that this condition can do to your engine, drop the plug heat range.

Shiny little diamond like deposits: It's too late you've already started to blow the pistons out of it. Start over from scratch, fatten the carb, back-up the timing and cool down the plugs. Now start a proper tuning procedure and hopefully you caught it before too much damage was done.

No color mark on ground strap: If your showing good color on the porcelain but the ground strap fails to show an indicator then your plug is too cold, go up 1 heat range.

If the ground strap is showing a good color line but the porcelain is showing no color at the base then your plug is too hot, drop down a range.
I will use maybe 3 different ranges on one bank, make a pass and from those three different plugs determine which one is correct for the engine.

Variable heat readings: On a small block motor most have adjoining exhaust ports, these will always be your hottest cylinders and in some cases where there has been excessive port work and thinning of the metal between the ports it may be necessary to run a plug one step cooler in those cylinders, use a plug indexing washer to back the timing down in those cylinders slightly, or if you have an adjustable ignition system you may want to electronically back the timing down in the hot cylinders.