Editing Reading spark plugs (section)
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==Tuning an engine by reading the spark plug== When tuning a performance engine the spark plug coloring and condition is a important tuning aid. This article will cover the basics of spark plug reading. It will require the vehicle be run on a drag strip at wide open throttle. Use common sense, do not endanger yourself or anyone else during the procedure, follow all laws and track rules regarding safety. To get an accurate plug reading, you must always use a NEW plug. However, a complete set of plugs doesn't need to be used for every pass. As long as the fuel distribution is even across all the cylinders you can replace one plug, or two plugs (one from each bank). To get a usable WOT plug reading, the engine should be shut down immediately after the full throttle run and coasted to a stop or towed back to the pits. This is known as doing a "plug chop". If the engine is allowed to idle, the reading will be skewed. When tuning by the spark plug, there are two major variables that will be taken into account: *air/fuel ratio *ignition timing {{!}}It's important to only change one variable at a time so the results can be tracked. Keep a written log of the changes and their effect. Don't rely on memory. ===Areas of the plug to inspect=== *The ground strap will show a color change in two spots on the 90 degree bend **The first mark furthest from the plug body shows the '''initial''' (or base) timing **The second indicates '''total''' timing {{Warning}}If the second mark is all the way to the base of the ground strap where it attaches to the plug body, this is a sign the plug got too hot. An ideal 'safe' timing range is when the total timing discoloring is located just past the bend. [[File:Timing indicator mark1.jpg]] Next, inspect the threaded area for the heat range. The threads will show a dull burnt-looking color change, 2-3 threads is ideal. *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 [[File:Heat range2.jpg]] <br> Indicators for the air/fuel ratio can be found in two spots, one spot known as the '''''air/fuel ring'''''. On the air/fuel ring, you're looking for a complete 'full turn' of discoloration. Ideally this should be lightly colored soot. As the fuel ring soot darkens, this indicates a richer air/fuel ratio. If you're tuning the engine for maximum horsepower, the ring should be very light and not make a full circle around the ring.<br> {{Warning}}Use caution when approaching a borderline too-lean condition. A ''little'' lean can make good power, but being '''too''' lean can melt a piston. [[File:Air fuel ring3.jpg]] The second place to inspect for the air/fuel ratio is the the porcelain. Being too rich leaves light to dark color rings on the porcelain. Ideal conditions leaves the porcelain like new to shiny white. <br> {{Warning}}Beware of grayish or peppery speckles as this is most likely molten piston material being deposited on the porcelain. The cause of this has to be corrected immediately. ===Example plug=== [[File:Example plug.jpg]] *'''1''' is a timing indicator, you'll see a definite color change on the ground strap right about at the arrow. Too much timing and the color change will be very close to the body of the plug, too little timing and it'll be closer to the tip. Ideally it'll be right at the 90 degree bend on the ground strap, in this image timing and temperature look good. *'''2''' indicates the base timing is ideal. *'''3''' shows another timing indicator; usually there's a brown ring right at the tip of the porcelain. It should be a sharp defined ring about 0.020" wide. A wider ring indicates not enough timing. If the ring is smaller, incomplete or nonexistent (like shown here), that could indicate too much timing. *'''4''' is a heat range indicator seen at the threaded portion of the plug. Looking at the threads you'll see that a few toward the end are a dull burnt looking color, and 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. If you're using a longer reach plug, 2.5 to 3 threads is optimum. Too few colored threads indicates a too-cold plug; too many colored threads indicates a too-hot heat range. ===The air/fuel indicators=== [[File:3.jpg]] Divide the porcelain into three equal segments: top, middle, and bottom. *Top: This area is the idle circuit indicator. For a race engine, this area has no real application; race engines don't rely on the idle circuit the way a street engine does. However if you're tuning a street driven vehicle then this portion needs to be a dark gray/tan color. This is achieved by tuning the idle air/fuel ratio. This is done by changing the air bleed orifice size, changing the idle feed restrictions, adding or subtracting idle bypass air, or a combination of these things. {{Note1}}The initial timing has a direct effect on how much the primary throttle blades need to be opened to achieve a good idle. If the initial timing is insufficient, the transfer slot might be overexposed in an attempt to raise the idle speed sufficiently. An overexposed transfer slot will cause an noxious smelling, poor quality idle and poor off-idle response. *Middle: This is the area that will show the combustion chamber condition and air/fuel ratio at part throttle cruise (primary side only) with the power valve and secondaries closed. This is a high vacuum condition, vacuum advance will be fully activated. The mechanical advance may not be fully in. Usually about 30-50 MPH depending on the gear and weight of the car. *Bottom: This indicates the conditions at high load, low vacuum, open throttle settings. This is a priority if drag racing. Using a 5x or 10x scope you need to look right down to the bottom of the porcelain where it meets the metal body of the plug. This is the area that will have the color that you need to study and tune to. The other 2/3 of the porcelain will be burned clean by the high heat generated by WOT and high RPM, so cruise or idle characteristics will not show. Look for a colored ring at the base of the porcelain. The color will vary depending on the type of fuel: Unleaded E10 pump gas will leave very little color because of the additives like detergents, as well as the methanol. If using 108-110 octane race gasoline, 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 effect 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 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. This may also be seen with a new engine that hasn't fully seated the rings yet, just don't confuse this with the fuel ring. ===Other tell-tail signs of plug condition=== [[File:Autolite-hot6.jpg]] [[File:Saltandpepper7.jpg]] Shiny or glazed deposits: This occurs from excessive idling or rich idle condition leaving heavy soot deposits. If excessive and not cleaned or the idle air/fuel ratio corrected, these deposits can cause excessive porcelain temperatures as they oxidize, causing the glass to melt. This in turn can cause down-track popping through the exhaust. This glazing on the porcelain actually becomes a conductor and the spark will jump from the electrode to the porcelain resulting is a very weak, small spark if any spark at all. You will usually see splotchy deposits on the plugs after the run, either green or yellow in color along with the tell-tale shiny glaze. Remember, the porcelain should always have a chalky or dull finish. Base of threads sooty: This is usually a indication of the plug not being tight enough, allowing air to be pulled in to the chamber and air/fuel being pushed out. Change the plug, tighten to spec. This area should have a nice dark to medium gray color without heavy deposits. [[File:Rich18.jpg]] Black or brown specks: This is an indication of detonation which is caused by ignition timing that is too advanced for the air/fuel ratio or octane of the fuel. Detonation (an undesirable, uncontrolled combustion of the air/fuel mixture after the ignition event) causes the boundary layer of air within the cylinder to be disrupted, which in turn causes the components and surfaces within the cylinder to absorb heat from the combustion process and increase in temperature. The black spots are the result of oil deposits bypassing the piston rings during detonation and being fused onto the porcelain by the increased cylinder temperatures. Tiny beads of grey/silver material apparent on the porcelain are melted piston. Reduce the ignition timing, richen the mixture, increase the octane of the fuel or a combination of all of these to prevent this situation. {{Warning}}Do not underestimate the damage this condition can cause your engine. Correct this by whatever means necessary. [[File:AR3933-terry-wise-plug19.jpg]] Shiny little diamond like deposits: It may be too late, the pistons have begun to disintegrate from the heat and/or detonation. If the engine doesn't exhibit symptoms of a pinched rings or broken ring land (smoking exhaust, excessive blowby, low compression reading, excessive leak down), back up and start over with the tune of the engine by doing one or more of the following: *Lower the air/fuel ratio to a safe level *Reduce the timing *Use a colder plug heat range 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 may be 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. [[File:How to read spark plugs10.jpg]]
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