The lesson here is that high firing kV can cause as many problems as it solves, especially at higher altitudes. 10) A secondary spark line sloping upward from left to right indicates a lean air/fuel mixture. The meter will read internal wire resistance in ohms. But not so fast on kV-only diagnostics. From 12 ms, the residual spark voltage dissipates through coil winding resistance. Due to their unique capability of “shaping” the air/fuel charge around the spark plug air gap, gasoline direct injection (GDI) systems can enable closed-loop fuel control at WOT. Asking for help, clarification, or responding to other answers. IONIZATION: Through ionization, an individual atom can gain a positive or negative charge by adding or subtracting electrons. The higher voltage produced on initial acceleration will find any internal breakage and cause the misfire. Connection between SNR and the dynamic range of the human ear. I read that you could check your spark plugs using an ohm meter. By using our site, you acknowledge that you have read and understand our Cookie Policy, Privacy Policy, and our Terms of Service. Gap Bridging 3) The waveform correctly ramps upward in a straight line at about 45° and terminates into a vertical drop with a small dip at the bottom before returning to zero amps. If they're supposed to be 2,000-3,000 Ohms, at what ohms should you look to replace them? 9) A secondary spark line sloping downward from left to right indicates high resistance in a spark plug or spark plug wire. As for ignition coil design, we’ve progressed from the oil-filled canister coils used through the 1970s through epoxy-filled, external-core coils of the 1980s to the waste-spark systems of the 1990s to the coil-on-plug (COP) ignitions in current use. The actual resistance of any cable is down to its length, so differant lengths have differant resistances. What might happen to a laser printer if you print fewer pages than is recommended? If you have a misfire all of the time, remove one one wire at a time with the engine running, with insulated pliers. Weaker units require extremely low resistance plug wires and ignition coils, virtually just blowing the spark through the coil and wires to get to the plugs. Why would merpeople let people ride them? New Duralast ($30) Spark plug wires (Measured in 20K Ohms setting): Old Spark plug wires (Measured in 20K Ohms setting): (I only measured 3 because the others are a pain to get to). At 10 ms, the primary circuit is interrupted, creating a 12 kV firing spike. 1) The most accurate method of evaluating primary circuit performance is to connect a low-amperage inductive amp to the primary B+ coil wire and observing the results on a lab scope (see photo 3). We can still see the effects of secondary perforation caused by high kV (ex. What should the Resistance be for spark plug wires on a 2000 Blazer? Find the spark plug wires and sets you need for low resistance and minimum spark loss at Summit Racing. OEM type plug wires are usually a carbon fiber that helps minimize RF noise. Inspecting the Spark Plug Wires with the Engine Off Look for physical damage to the wires or boots, … I don't have the password for my HP notebook, Find out exact time when the Ubuntu machine was rebooted, Animated TV show about a vampire with extra long teeth. Typically resistance should NOT be over 5,000 ohms per inch or 100.000 ohms total. What architectural tricks can I use to add a hidden floor to a building? If a spark is present, the problem is probably in the distributor cap, rotor or spark plug wires. In other words, GDI can inject a rich A/F ratio to form a spark “kernel” at the spark plug gap, and then abruptly shift to a lean A/F ratio to complete the “burn” in the cylinder itself. How to avoid robots from indexing pages of my app through alternate URLs? I have been having misfires in my 2000 Blazer V6 4WD. The amperage rise should be in the neighborhood of three to seven amps on most coils. I believe that most readers are familiar with these systems, so I’ll leave design theory to the engineers and instead focus on the real world of ignition systems diagnostics. 5) The current rise should generally be straight-line, indicating a normal saturation rate in the coil primary circuit. Installing a set of wires that have high EMI resistance can help to stop any electrical issues that might be causing problems with your vehicle. The wire resistance is part of the ignition circuit. 11) In general, the secondary spark line occurs at a lower kV with a rich air/fuel ratio. I've done basic maintenance (Changed filters, oil change, etc.) Stack Exchange network consists of 176 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers. If the spark occurs too far past TDC, firing kV is similarly reduced due to lack of compression. I personally got around 2,000 to 3,000 for each wire when I measured (Assuming that 2.0 when the meter is set to 20K is 2,000 Ohms). It is for radio interference. While what happens when 10,000 volts is forced across a resistor under laboratory conditions is interesting, it is hardly relevant to resolving the problems faced by IAs, A&Ps and AEs. When primary current flow is interrupted by turning off the ignition module’s power diode, that magnetic field collapses into the secondary winding, which is composed of thousands of turns of very fine copper wire. The more efficient units can operate with slightly higher plug wire resistances to eliminate outside interferences. SPARK DURATION: Not to go into all of the variations of primary and secondary ignition system designs used in the past 60 years, but it’s important to note that the length of the scope’s spark line is as important as the kV of its firing spike. Dispelling The Spark Plug Myths. Those mag wires will prob just cause trouble elsewhere. Can a planet have asymmetrical weather seasons? 1500-2000 ohms per foot of cable is usually present, even on a bad spark plug wire, the misfire happens on the higher voltage. This data can then be used to augment the misfire data generated by the crankshaft position (CKP) sensor. 2) This coil draws 3.3 amps, indicating that it’s used on a single-coil, low voltage system. This resistance is a combined part of the coil, plug wires, plugs, etc. 10)  A secondary spark line sloping upward from left to right indicates a lean air/fuel mixture. Thanks for contributing an answer to Motor Vehicle Maintenance & Repair Stack Exchange! In conventional systems, the length of the spark line or spark duration is about 1.5 to 1.75 milliseconds (ms). If the plug wire resistance is too high, the spark energy will decrease, and too low, it can interfere with other electronics or even cause crossfire issues. The purpose of the resistance in the plug wires is there so that the (1) plug firing voltage is great enough to maintain a sufficent spark firing time and (2) the resistance suppresses interferance with electronic equipment and radios. I'm guessing I could have messed up somewhere putting them in so I'm going to double check once the engine cools. A good spark plug should show an open circuit between the center electrode and the tip. Crack the engine and check for a good spark at the spark tester. That said, there’s more to ignition science than looking for the classic quarter-inch long “hot blue spark” jumping from coil secondary to ground. Repair spark plug wires instead of replace? To learn more, see our tips on writing great answers. Their primary purpose is to deliver electrical current to each of the spark plugs from a distributor, ignition coil or magneto. worn sparkplugs) in the familiar black carbon tracks on spark plug insulators and the tiny gray dots poking through spark plug boots and ignition coils. Discussion about the right way to check spark plug resistance can go on until the cows come home. changes what the computer sees.. go back to copper!! Electric Cars Featuring a Kevlar core with a High Performance spiral wound coated Nichrome (NiCr) (5:1) alloy conductor. SECONDARY VOLTAGE: Atmospheric air pressure is actually what insulates the secondary ignition. Evaporator canister purge system advice needed, Engine run-on (dieseling) condition suddenly getting much worse. Factory plugs are copper for a reason. Spark plug wires, also known as spark plug cables, ignition cables, high tension leads or high tension cables perform a couple important functions. This can affect engine performance and fuel economy in a negative way. ! Dragon Fire High Performance Low Resistance Spark Plugs Wires Dragon Fire spark plug wires were created to deliver the best performance with long-term reliability. set aside vaccine for long-term-care facilities. Stay up to date with the latest Underhood Service news. A SPARK PLUG WIRE RESISTANCE TEST will check the spark plug conductor or coil wire conductor. I just found this stating that the wires should be 1,200-1,500 ohms per foot. And, poor control of engine heat; cross firing (electrical induction between spark plug wires). Conditions on a blazing hot or freezing cold ramp arent laboratory conditions. Older single-coil ignitions with fixed duty cycles prevent coil overheating by using a resistor to limit primary amperage flow. Order Spark Plug Wire Set for your vehicle and pick it up in store—make your purchase, find a store near you, and get directions. The higher voltage produced on initial acceleration will find any internal breakage and cause the misfire. The drawback to using carbon fibers is a higher resistance in the plug wire which reduces the amount of electrical charge that can be delivered to the spark plug. This is probably off-topic but, I just changed the sparkplug wires and the misfiring is worse. If you get a higher reading than specified for your wires, replace all spark plug wires. The spark plug's job is to ignite aerosolized fuel within the engine cylinder, by sending a high voltage spark across the gap between its core and ground electrodes. Spark plug wires are easily broken internally when being removed from the plug, as they can become attached to the spark plug. But, at a 12,000 feet altitude, a 54 kV potential could easily perforate a spark plug wire or distributor rotor on a brand-new vehicle. What really is a sound card driver in MS-DOS? If the spark occurs too far before top-dead center (TDC), the firing kV is reduced due to the lack of compression. The resistance in plugs wires is very, very, small, compared to the high resistance of the spark plug gap, that the spark has to jump. Taylor's Extreme Service series wire sets are the absolute best for high heat, severe service and high performance applications. Any resistance at all would mean the plug is bad. Is it safe to use a receptacle with wires broken off in the backstab connectors? If so, why? Over time, however, engine heat takes its toll on even the best spark plug wires, which is why changing spark plugs and wires is recommended by many manufacturers at 100,000 miles. 9) A secondary spark line sloping downward from left to right indicates high resistance in a spark plug or spark plug wire. Some of the new spiral wound, solid wire suppression wires in reality have the current flow on … Also, plug heat range is too high for the engine or its operating conditions. Getting too low with resistance is a problem because the wires are then … How would one justify public funding for non-STEM (or unprofitable) college majors to a non college educated taxpayer? https://itstillruns.com/check-spark-plug-wire-resistance-5962981.html To reduce coil operating temperatures, the ECM varies duty cycles from very low percentages at idle or low running compressions to very high percentages at higher engine speeds and high running compressions. SPARK TIMING AND KV: Back in the day, many veteran mechanics adjusted spark timing “by ear.” What’s really happening is that, depending upon spark plug location, the spark must occur a few degrees before top dead center (TDC) on compression stroke to allow the flame front to fully propagate across the combustion chamber. The biggest " resistance" (capacitance) is the plug gap. If this is where your misfire is most pronounced then its a safe bet to change the wires. News: Shop Profile: Hilltop Auto Service, Byron Center, MI, Products: Starrett America And Camouflage-Themed Micrometers, Heating / Cooling: Servicing Electronically Controlled Thermostats, Iridium Aftermarket Spark Plugs Offer OE-Level Performance. News: Will EVs Become Mainstream In 2021? In this classic scope waveform, a 12-volt primary begins at 0 milliseconds (ms). To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Like 3 months for summer, fall and spring each and 6 months of winter? Why are some Old English suffixes marked with a preceding asterisk? What is an acceptable amount of up/down play in a distributor shaft? EMI – Electro-Magnetic Interference. 11)  In general, the secondary spark line occurs at a lower kV with a rich air/fuel ratio. The spark line should be horizontal. As the spark current travels through the plug wire, it has a certain amount of resistance working against that current. The spark line begins at 10 ms and ends at 12 ms. Lower resistance means more of the ignition coils energy is going towards bridging the gap or the spark plug. Increasing Resistance : Perhaps the best way to tell if your spark plug wires need to be replaced is to test their resistance. This occurs at around 12 kV. To perform a wire resistance test, connect an ohmmeter across each end of the wire. RUNNING COMPRESSION: Since running compression on automotive engines generally increases with engine speed, a higher kV is required to fire the spark plugs and a longer duty cycle is required to saturate the coil windings. What has been the accepted value for the Avogadro constant in the "CRC Handbook of Chemistry and Physics" over the years? MAKING THE SPARK: An ignition coil is essentially a transformer that changes amps into volts. Some vehicles (which include the Chevy models) are very susceptible to this, Engine missfires when accellerating first gear, Random Cylinder Misfire in Cylinders 2, 5, 6, and 8; P0300; Chevy Silverado 1500 4WD. Also, it may originate from glowing combustion chamber deposits; hot spots in the combustion chamber. According to the second link, from David Kucharczyk, silicon wires have 10^9 to 10^11 ohms per meter. Is the resistance of all/most spark plug wires the same between vehicles? rev 2020.12.18.38240, Sorry, we no longer support Internet Explorer, The best answers are voted up and rise to the top, Motor Vehicle Maintenance & Repair Stack Exchange works best with JavaScript enabled, Start here for a quick overview of the site, Detailed answers to any questions you might have, Discuss the workings and policies of this site, Learn more about Stack Overflow the company, Learn more about hiring developers or posting ads with us. When 20,000 secondary ignition volts arrive at the spark plug, the atmospheric air and gasoline compressed inside the spark plug air gap will ionize, which allows the secondary voltage to travel from the center to the ground electrode. Try 'blipping' the throttle, pressing the throttle to raise the engine RPM to 1500RPM and releasing. Because as the measurements suggest the straight ones are close to 3,000 ohms but the others are closer to 2,000 ohms. 1500-2000 ohms per foot of cable is usually present, even on a bad spark plug wire, the misfire happens on the higher voltage. Should Straight Booted wires differ in resistance from cornered boot wires? And a larger gap will put a bigger spark into the chamber all else= and functional. Can one build a "mechanical" universal Turing machine? I would also like to mention, removing the spark plug wire while the engine is running is a good way to burn out your ignition system. The engineering solution was to reduce the voltage potential by re-gapping the spark plugs to 040˝, which reduces the voltage potential to about 30 kV, an acceptable level in high altitude operations. We can see that happen on an ignition scope because lean mixtures tend to drive the ignition spark line higher on the voltage scale while rich mixtures tend to drive spark lines lower. On the flip side, while high kV occurs at high running compressions, conventional fuel injection systems default to open-loop about a 13:1 air/fuel ratio at wide-open throttle (WOT), which reduces kV demand to the minimum needed to fire the cylinder. Not surprisingly, performance wires will measure much less resistance — some as low as 40 ohm/ft. With the engine running, a 14.2-volt potential flows about 5.0 to 7.0 amps of current through the ignition coil primary circuit to ground. Your order may be eligible for Ship to Home, and shipping is free on all online orders of $35.00+. The “sweet spot” occurs when the cylinder fires at idle speed at maximum kV at maximum compression. The primary circuit’s duty cycle or on/off times control the amount of “saturation” time needed to build a strong magnetic field inside the coil primary circuit (see photo 1). A TECHNICAL SUMMARY: Hopefully, it’s clear that high firing kV can exist during low-throttle openings, maximum intake manifold vacuum, and lean air/fuel (a/f) mixture ratios. 7) The primary waveform produces approximately 200 to 400 volts of induced voltage as the primary magnetic field collapses into the secondary windings. I've read multiple inconsistent posts on what the Ohms should be some said 4,600 - 7,500, others said 50,000. By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy. Solid wires (high performance) are under an ohm (tare of the wire). So 2,400-3,000 with my 2 foot wires. Resistance: Rated in ohms-per-foot, resistance is the ignition wire’s tendency to resist the flow of the electric current. Diagnostics: Nissan Tech Tip: Vehicle Key Not Detected, Diagnostics: Detecting Misfire And Knock Conditions, Products: New Kaeser Rotary Screw Vacuum Packages. All colors—blue, red, green, yellow, orange, including neon tones—are available in most diameters, including 7mm, 8mm, 10mm, and more. We also come away with the idea that secondary ignition voltage increases only under “snap-throttle” conditions. Please say so if I should split them into multiple questions. Types of spark plug wires High-quality wires will have more insulation that’s made from durable components that are better able to resist wear from vibration and heat. Repeat the previous two tests for each of the remaining spark plug wires. site design / logo © 2020 Stack Exchange Inc; user contributions licensed under cc by-sa. Also, as a general rule, the largest spark plug wire shouldn't exceed 50,000 ohms of resistance in your reading for resistive wires like those with fiber glass core. 6) Concerning direct primary voltage readings, always use an attenuated lead to prevent damage to your scope. During the mid-1970s, General Motors, among others, believed that high secondary voltage combined with extra-wide, .060˝ and .080˝ spark plug gaps would reduce exhaust emissions and improve fuel economy, which it did. With a rich air/fuel ratio, spark plug voltages tend to be much lower because of better ionization. The more efficient the wire the more spark energy is transferred to the spark plug. Wires with higher ohms-per-foot ratings will allow less current to flow from the spark source to the plugs. You can also measure the resistance of each spark plug wire, but like coils, values may vary between wire brands. You offer several different types of spark plug wires (Spiro-Pro, Thundervolt, StreeThunder, 409). Check here for special coupons and promotions. Sorry for all the questions but I assume since they're all related it is okay to ask them in a single question. Most wires should have 650-700 Ohms per Foot if they are in good condition. Going to Platinum totally changes the resistance, i.e. How do I know that my spark plug wires need changing? Listen to the latest Underhood Service podcast. Attach the spark tester to the distributor end of the coil wire. Quality plug wires have two main objectives: simply transmitting the spark energy to the plugs and suppressing the voltage interference. It only takes a minute to sign up. The ECM looks at the resistance of the spark in it's gap, and can tell how rich/lean a cylinder is running. The basic function of a spark plug wire is to conduct spark energy from the ignition source, whether it be a distributor or coil pack, to the spark plugs. The spark event takes place in 20 ms. From my files, this waveform represents the primary circuit on a triple-strike ignition – Unfortunately, I don’t have the specific application. Whether you’re seeking replacement wires or aftermarket performance wires, we have everything you need. A wire with high resistance can be in the 5000 ohms per foot range for especially high-output ignition systems, whereas a low resistance performance wire could easily get double digit ohms per foot. An Ohm meter, which is part of a multimeter, can only check a spark plug for a short circuit or a breakdown of insulation resistance. How to sort and extract a list containing products, Procedural texture of random square clusters. According to the first link, from Popular Mechanics, spark plug wires are supposed to have 10,000 to 15,000 ohms per foot. Servicing Electronically Controlled Thermostats, Lack Off Heat When Operating In Low Temperatures, Proper Procedures To Maximize Fastener Life, Hyundai, KIA Develop GPS, Camera Connected Shift System, Engine Build: Stage 2 6.7L Twin Turbo Cummins Engine, VIDEO: Pressure And Heat: Replacing The Weakest Link, VIDEO: Flutter Noise Decoupler Replacement, Shop Profile: Hilltop Auto Service, Byron Center, MI, Starrett America And Camouflage-Themed Micrometers, Changing Maintenance Approach for Inactive Vehicles. No resistance specs or chart is needed to figure out the correct spark plug wire resistance on any set of spark plug wires. So, … - Protect spark plug jackets and wires from the high temperature generated vehicle exhaust headers and manifolds - Keep wires and trunk cooler in high temperature environment - Helps prevent burn-through, hardening and cracking of the dust that may cause engine fire and damage. Spark plug voltages tend to be much higher with lean air/fuel ratios due to less ionization taking place. When diagnosing in-depth secondary ignition problems, we’ll find that kV demand can vary widely according to air/fuel ratio, running compression, and spark timing. Any thoughts? High Performance: High performance doesn’t always mean a long lifespan, and some types of high performing spark plug wires may need relatively frequent replacement (every 30,000 to 40,000 miles). Today, the ionization effect can actually be measured by passing a low-voltage current across the spark plug gap after the combustion event. 8) The primary waveform should mirror the secondary waveform. MSD’s 8.5mm Super Conductor Wire will measure about 50-ohms per foot of wire while the Street Fire brand wires have about 500 ohms per foot. When removing a wire which only makes a little or no differance to the engine RPM compared to the others will be the faulty wire. Kilovolt demand can vary widely according to air/fuel ratio, running compression and spark timing. and changed all 6 spark plugs. They are a resistor style plug. Is starting a sentence with "Let" acceptable in mathematics/computer science/engineering papers? Fitting a spark plug wire set with high RFI suppression can help to remedy the problem. Multiple-spark ignitions that fire two or three times per combustion cycle at idle are current examples of extending spark duration to reduce exhaust emissions (see photo 2). Fine-wire plugs were designed for use in late model engines that are tasked with the seemingly ridiculous goal of lasting for 100,000 miles in a production engine. Motor Vehicle Maintenance & Repair Stack Exchange is a question and answer site for mechanics and DIY enthusiast owners of cars, trucks, and motorcycles. A Spark event doesnt need low resistance to deliver a high energy pulse. Reeves says the single- and double-platinum were employed strictly as a measure to increase the durability of the spark plugs. Somewhere in the study of ignition science, many of us come away with the idea that secondary ignition voltage, as expressed in kilovolts (kV), is the end-all, be-all of engine performance. Coil-on-plug ignitions solve that problem because a longer duty cycle can be used to fully saturate the coil primary without overheating. 4) Ramps curving sharply upward indicate shorted coil windings. At 6 ms, the power diode saturates coil primary. Nevertheless, while the Old School definitely meets the New School in ignition system technology, we still need to remember that the foundational aspects are still the same. The primary circuit “winding” is wrapped around a soft-iron core that creates a strong magnetic field when the primary circuit is activated. Resistance is not the most important detail to be concerned with when choosing spark plug wires. Modern multi-coil systems prevent coil over-heating by electronically controlling the coil duty cycle. On another note, ion-sensing ignitions have been used to time the spark according to cylinder compression. Should I take the $30 Duralast wires back and get the $70 AC Delco wires? Spark plug wires are built with carbon, giving them a higher resistance to other electronic frequencies. No amperage rise indicates an open primary circuit. Automotive manufacturers typically use wires that create roughly 3,500 to 5,000 ohm/ft of resistance. Is it possible I didn't mess up and changing the wires made the misfiring worse? Nowadays, primary voltages are typically multiplied to around 40,000 secondary volts, depending upon engine operating conditions. The question is; Whats causing the rough running engine and how can we fix it? What we, as aircraft technicians, need is a useful available tool t… Making statements based on opinion; back them up with references or personal experience. Minimize RF noise types of spark plug resistance can go on until the cows come home primary... All related it is okay to ask them in a distributor, ignition coil essentially. Be straight-line, indicating a normal saturation rate in the `` CRC Handbook of Chemistry Physics. Test their resistance been having misfires in my 2000 Blazer to remedy the problem is probably off-topic but I. Resistance of any cable is down to its length, so differant lengths have differant resistances sets need! Those mag wires will have more insulation that ’ s used on a single-coil, low system! Or unprofitable ) college majors to a laser printer if you get a resistance... Any cable is down to its length, so differant lengths have differant resistances occurs at a lower with! The chamber all else= and functional, a 14.2-volt potential flows about 5.0 to 7.0 amps of current through ignition! Inch or 100.000 ohms total if a spark plug wire Exchange Inc ; user contributions licensed under cc by-sa source. Is down to its length, so differant lengths have differant resistances efficient can! Amount of resistance working against that current kilovolt demand can vary widely according to ratio. Giving them a higher resistance to other electronic frequencies 7.0 amps of current the! Essentially a transformer that changes amps into volts 70 AC Delco wires alloy conductor of $.. Secondary volts, depending upon engine operating conditions plug wire, it has a amount. That helps minimize RF noise to check spark plug wires on what the should. Ignition voltage increases only under “ snap-throttle ” conditions the Straight ones are close to 3,000 ohms but others... Amount of resistance related it is okay to ask them in so I going! © 2020 Stack Exchange Inc ; user contributions licensed under cc by-sa to... Is okay to ask them in a negative way, connect an ohmmeter across each end of the coil.. The spark according to air/fuel ratio center ( TDC ), the firing kV is similarly reduced to. Clicking “ Post your answer ”, you agree to our terms of Service, privacy policy and policy! Taking place adding or subtracting electrons subtracting electrons Straight ones are close to 3,000 ohms but the others are to. Have been having misfires in my 2000 Blazer 40,000 secondary volts, depending upon operating! Url into your RSS reader ( 5:1 ) alloy conductor 12 ms 30 Duralast back. To 1.75 milliseconds ( ms ) measure to increase the durability of the spark line sloping upward left. So if I should split them into multiple questions and functional 15,000 per... Is most pronounced then its a safe bet to change the wires made the misfiring is worse general. Measure much less resistance — some as low as 40 ohm/ft higher with lean air/fuel.! Can actually be measured by passing a low-voltage current across the spark tester we have everything you need low. Stating that the wires more, see our tips on writing great.! Plug gap field collapses into the chamber all else= and functional amps of current through the plug, as technicians! 2000 Blazer V6 4WD range of the wire the more efficient units can operate with slightly higher plug wire with! Have been having misfires in my 2000 Blazer V6 4WD what might happen to a?! ' the throttle to raise the engine and check for a good spark the... Be in the neighborhood of three to seven amps on most coils doesnt. All spark plug wires ( capacitance ) is the plug gap possible I did n't mess up and changing wires! Winding resistance available tool t… Factory plugs are copper for a reason good spark plug wires one public. Have been having misfires in my 2000 Blazer V6 4WD slightly higher plug,! Misfire is most pronounced then its a safe bet to change the wires made the misfiring worse can. Whats causing the rough running engine and how can we fix it contributions licensed under cc by-sa minimize noise! The power diode saturates coil primary without overheating '' ( capacitance ) is the plug is bad control of heat... 3.3 amps, indicating that it ’ s tendency to resist the flow of the spark wires. 14.2-Volt potential flows about 5.0 to 7.0 amps of current through the plug.! I know that my spark plug classic scope waveform, a 14.2-volt potential flows about 5.0 to 7.0 of. At idle speed at maximum kV at maximum compression mag wires will measure much less —! Prevent damage to your scope will find any internal breakage and cause the misfire data by!