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Thread: Ultimate Spark Plug Reading Thread

  1. #1
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    Thumbs up Ultimate Spark Plug Reading Thread

    Found an excellent thread with a lot of good info on the subject. All the info posted here is in credit to the following: http://www.ferrarichat.com/forum/sho...d.php?t=121401
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    This is only valid if you shut-off the engine after the finish line then tow the car back to the pits where you remove the plugs for reading !!
    Or if you are on the dyno
    VALID ONLY for full load acceleration or steady state dyno tests

    Plugs are best viewed with a 10x power illuminated magnifying glass.


    The "Ground Strap" [side electrode] = Heat Range
    The "Plug's Base Ring" [circle at the end of threads] = Mixture
    The "Porcelain" [white insulator] = signs of preignition/detonation

    Heat Range
    Heat Range = Ground Strap, the ground strap indicates the heat-range of the spark plug. If the "color" of the ground strap "changes" too close to the ground strap's end, (which is above the center electrode), then the heat-range is "too cold", meaning that the strap is loosing heat too quickly to the base ring, and is not able to burn off deposits until near its end. [plugs that are too cold will eventually foul the center electrode and white insulator, leading to misfires]

    If the "color" of the ground strap changes near where it is welded/attached to the base ring (last thread ring), then it means that the plug heat-range is "too hot", because heat is not being transferred/cooled from the strap to the base ring quickly enough !!!! The strap might begin to act like a "glow-plug", eventually causing preignition and/or detonation later on.

    Proper heat-range is when the "color" is at the halfway point on the ground strap, neither too cold or too hot.

    (Color = meaning the evidence of heat/or lack of heat by the appearance dark vs lightened color of metal)




    Mixture

    The air/fuel mixture ratio shows up on the base ring (the last thread ring, it has the strap welded to it). You want a full turn of light soot color on the base ring!!! If you want to tune for max. power, then you want 3/4 to 7/8ths of a full turn of light soot color to show up on the base ring, but this is on ragged-edge of being too lean, but will make the most HP on most engines.

    To be safe, leave it at a full turn of light soot color. If the base ring has a full turn of color, but there are "spots" of heavy buildup of "dry soot" on top of color, then mixture is too rich .


    If the base ring has a full turn of color with some spots of heavy dry soot, then mixture is too rich, REGARDLESS, if the porcelain is "BONE-WHITE"


    Preignition/Detonation

    Porcelain = the porcelain shows up preignition/detonation, it will not accurately reveal mixture/air/fuel ratios. To look for the first/beginning signs of detonation, search the white porcelain for tiny black specks or shiny specks of aluminum that have fused to the porcelain.

    When detonation occurs, part of the air/fuel mixture explodes instead of burning, the explosion is heard as a "metallic knock", this audible knock is the result of a sound shock-wave, this shock wave travels back and forth across the clearance volume "disrupting" the cooler boundary layer gases that cover the entire clearance volume area. This disruption allows "more" heat to be transferred into parts, especially, domes/piston tops,...along with the very rapid rise in pressure like a hammer blow, pistons can get torched with melted sides and holes !!!

    With the early signs of detonation, the shock-wave will also rattle rings causing the tiny amounts of oil that now gets by rings, to be fused to the white porcelain as tiny black specks, also fused as specks are soot that was clinging to clearance volume surfaces in the relatively "still-air" of the boundary layer. One step beyond the black specks, will be tiny specks/balls of aluminum coming off the pistons that will be fused to white porcelain,....the next step to be reached is occasional pieces of the porcelain being broken-off as detonation gets worse, ETC. Soon after that are holes, blown head gaskets, broken connecting rods, ETC.

    Center Electrode = the very tiny sharply defined porcelain -"ditch" that encircles the center electrode, will also show up early signs of preignition/detonation and the wrong heat-range. Look for signs of the ditch beginning to be filled up with melted porcelain, you will need a 5x or 10x magnifying glass.


    Ideal heat range/mixture/timing:


    Carbon Fouled

    Soft, black, sooty, dry-looking deposits indicate a rich air fuel mixture, weak ignition or wrong heat range spark plug (too cold). These carbon-based deposits are conductive, much like oil fouling, and will allow the voltage coming out of the center electrode of the spark plug to track down the core nose rather than jumping the gap. This will result in an engine misfire and further aggravate the carbon fouled condition.

    Check for correct plug heat range. On fuel injected engines, check for sticking injectors, malfunctioning cold start valves and/or circuits. Also check for correct fuel pressure specifications.

    On computer controlled vehicles, the "limp home" computer mode will always result in a rich condition. Therefore, it is imperative that you check the operation and condition of the on-board computer system.

    On all engines, severe vacuum leaks can decrease manifold vacuum, resulting in a rich condition. Weak and/or damaged secondary ignition systems will fail to spark across the gap lowering combustion chamber temperatures and promoting carbon deposits. This condition could also result from continuous low speed driving or poor cylinder compression.


    Fuel Additives

    Red to purple deposits on one side of the core nose are an indication of a fuel additive. While many of these deposits are non-conductive and do not contribute to lack of performance, some fuel additives contain octane boosters that leave conductive deposits on the core nose. Care should be taken to select fuel additives which are compatible with ignition systems and do not contain conductive materials such as octane boosters.


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    Lets analyze this plug, sorry the numbered points aren't clear but it's 1-4 you can figure it out.

    #1 Is a timing indicator, you'll see a definite color change on the ground strap, it doesn't show well here but you can still see it right about at the arrow. Too much timing and the color change will be very close to the threaded body of the plug, too little and it'll be closer to the tip. Ideally we want it right in the apex or center of the 90 bend on the ground strap. This plug shows too much timing for the combustion chamber efficiency or octane level.

    #4 arrow shows another indicator of timing, you'll usually see a brown ring right at the tip of the porcelain area it should be a sharp and defined ring about .020 wide. Wider indicates not enough timing and any smaller , or only 1/2 way around or nonexistent as in this image is the second indication of too much timing in the motor.

    #2 The tip of the ground strap is loaded with OIL deposits, fuel deposits are usually flat black in color and almost like a fine powdery deposit, this motor is leaking oil into the combustion chamber, bad valve guides, leaking valve covers allowing oil to seep through the plug threads, whatever it needs to be fixed.

    #3 The threaded portion of the plug gives you the heat range, look at the threads you'll see that a few toward the tip are a dull burnt looking color the rest are black and shiny. You want about 2 threads showing the heat on the end of the plug and the rest of the threads to be shiny, this plug is impossible to read because of the oil mess. If you using a longer reach plug than this one 2.5 to 3 threads is optimum.
    To increase the number of burnt threads increase the heat range of the plug, if you have 4-5-6 threads burnt you need to get a colder plug.

    Looking at the color of the porcelain I'd give this carb a passing grade at the mid range and not to bad on the idle circuits although that dam oil leak makes it tough to really get a good read. I'll get some better shots for lesson 2.


    2nd Plug Example

    The plug is showing me by the deposits on the tip of the electrode and also the deposits right on the edge of the threaded body.
    that it's slightly fat at idle.

    The white porcelain is showing a lean condition at WOT, it's not too far advanced as the total timing mark or color change is right in the apex of the ground strap curve. The Idle timing is shown by the triangular hazing up on the flat of the ground strap and without even looking at the distributor specs I can tell you that the timing on this SB Mopar is about 18-20 initial and 34 total.

    I would need a better picture of the threads to determine the heat range.

    Changes:
    I would try and lean it out just a touch at idle and up the jets by 2 points to fatten up the WOT circuit.

    That slightly lighter color at the tip of the ground strap indicates too much gap, nothing serious but next time you change plugs I'd go to about a .036 gap from the current .040. Too much resistance caused by too wide of a plug gap can cause excessive heat on the tip which will shorten the life of the plug and really give you no benefits. I believe excessive plug gaps are not required on most Muscle and bracket cars, once you get into real big compression and major power you would open up the gap and replace plugs 2-3-4 times a year.


    Let's look at the Images below.......
    Note the change of color on the ground strap and it's position, this shows a timing issue. Unfortunately the reader who sent this image in didn't say what engine he was working on but by the condition of the plug I would guess a Small Block Chevy, 3 years old with 38* total timing and an Edelbrock Carb......I'm sure he will respond :-)

    In the second image I used a green arrow to show the area where we want the timing mark to be on this engine and of course you can see that the motor has too much timing.

    Image 3 shows only one thread heated on the plug and rest are oil soaked and wet this normally indicates that the plug is too cold, the oil indicates a valve cover leak and a New set of Cometic Aramid fiber gaskets would cure it.




    ------

    The color on the plug indicates a decent idle A/F ratio and a good ignition system probably an MSD or some other type of aftermarket ignition. The hot spark is keeping the porcelain clean on the top area anyhow. Now if we look down into the bottom of the plug as seen in the above image where the porcelain reaches below the steel body we see black deposits indicating a rich condition at mid range to WOT. I would guess this engine is a little lazy in mid range and could get better mileage.

    Changes:
    Back off the total timing but keep whatever the initial is as it appears pretty good, I would shorten the total by 4* and do another check.
    Fix the oil leak
    Go up one heat range and after about 50 miles check to see if you have 2-3 threads heated up and discolored for correct heat range. Heating up the plug will help reduce the carbon build up and further tuning with the A/F ratios can be done

    Before you can really tell what to do with the carb the ignition must be right as well as the correct heat range on the plug to get true readings.

    ...and check your Idler arm it appears to have some slack in it and your left rear tire needs 3# of air.


    -------

    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.

  2. #2
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    Good call man!!! Something this forum could benefit from.

  3. #3
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    Wow, I learned a lot!! About, all I knew was if there are speckles then you have detonation and if about 4 or 5 of the first threads on the spark plug are burned then you need a colder plug!

    This needs to be stickied!!!
    Last edited by BadBoostedBmwM3; 08-04-2009 at 12:03 AM. Reason: Automerged Doublepost
    This is my signature....

  4. #4
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    Quote Originally Posted by M3 Muscle View Post
    Good call man!!! Something this forum could benefit from.
    did you read that all already or just liked the thread idea ?

    I couldn't bring myself to read it til i need it, so just wondering lol

  5. #5
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    That is the best write up on plugs yet. Now everyone can become a tuner. Not all tuning is based off of O2's. ///J.T.///
    Lot's of new stuff hope it stays together a little longer. LOL

  6. #6
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    This thread needs to be stickied!
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  7. #7
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    Quote Originally Posted by Captain View Post
    did you read that all already or just liked the thread idea ?

    I couldn't bring myself to read it til i need it, so just wondering lol
    I glanced over it quickly. I have a couple books that have most of the info. It just wanted to post up that I thought it was something that this forum could benefit from.

  8. #8
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    Excellent thread, I shall be pulling my plugs and reading them after every few dyno pulls.

    Thanks sir.

  9. #9
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    cool pics. too drunk to read.

    saves place for comment tomorrow.
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  10. #10
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    When you do read the plugs, its best to go for a quick drive and pull over and pull the plugs. If you drive 150 miles and then pull them out, you will have no idea what driving caused them to look the way they look. I used to go out on the highway, pull, pull over, and pop one plug out of #1 and see.

    Good thread - most people don't realize how much you can see while reading a plug.


  11. #11
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    Yea you're suppose to pull them right away, do a WOT pull, shut off, pull aside and check the plugs.
    If you were to check only 1 plug, it should be #6.
    Turbo E30s. The New Supercars.
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    Sriracha is too hot for me.

  12. #12
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    thats alot of great info! Thanks alot

  13. #13
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    Quote Originally Posted by Tchao View Post
    Yea you're suppose to pull them right away, do a WOT pull, shut off, pull aside and check the plugs.
    If you were to check only 1 plug, it should be #6.
    What makes you think #6 is any different than #1?


  14. #14
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    Usually in our case, #6 is the hottest and most prone to bad situations. Therefore if there is any wrong, it might show up on #6 first or be the most evident.
    Turbo E30s. The New Supercars.
    Quote Originally Posted by mazur
    Sriracha is too hot for me.

  15. #15
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    holy smholy! good stuff indeed

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