Testing a spark plug wire’s ohm resistance with a multimeter is a good way to verify they are in working condition, and if the wires are capable of delivering the required voltage to the spark plug. You should get a reading between 11.3M (11,300) - 15.3M (15,300) Ω's. Place one lead on the post where the spark plug wire goes. Types Of Spark Plug Wires The most popular aftermarket plug-wire construction for street vehicles — and even race cars — are spiral-wound wires. Then multiply the Ohms per inch by 12 to get the Ohms per foot. Either you will be at one extreme or the other. One last check should be to verify that the resistance of the plugs is below 5,000 Ohms. All of the above readings would put you in a normal range. Testing Plug Wires: If you have access to a factory service manual for your car, you may find a resistance rating for the spark plug wires, (such as 1000 - 4000 ohms per foot). manufacturers' specifications). Although there are many different cases, if the insulation resistance between the center electrode and the shell is over 10 ohms, the engine can be started normally. Technician A says that a defective spark plug wire can cause an engine miss. Many things effect spark plug gap settings. Resistance values differ between manufacturers. We didn't get into testing ignition coils yet, but that's my next step to see if there's a difference other than the harness plug and the spark plug wire … Mine has 3 or 4 ohms.? If you have stranded wire and cut into it you will have stranded metallic wire. 50 or 100 ohms in the plug … Then the other small pin. Spark plug wires deliver thousands of volts – up to 45.000V, depending on the application – to the spark plugs. ... and the spark plug wire should be replaced. So 2,400-3,000 with my 2 foot wires. Here is a fast easy method to diagnose if your spark plug is the problem. Combustion engines -- like the one in your lawn mower -- require a spark to ignite the fuel the engine needs for operation. Again this may vary by a little .. but not too far from that. A quality spark tester, on the other hand, requires tens of thousands of volts to fire. if all checks out then check the coil with ohm meter. Replace any wires with resistance greater than 30,000 ohms which indicates that the internal conductor is failing. How to Check a Lawn Mower Coil With an Ohmmeter. When handling spark plug wires, never bend the wires at sharp angles as this can cause an internal break in the wire. 2 -1 ohms doesn't make sense. Typical secondary coil resistance specifications usually range from _____ ohms. If you know how to use an ohm meter, you can measure the plug wires resistance from end to end and see if … check with inline spark tester between the coil and the plug wires for fire. Consult a tune-up manual for exact specifications. This is a high enough amount of resistance to cut down on ignition noises, but not so high that engine performance suffers. 3) If you haven’t changed your spark plugs in 2 years or more, your problem could likely be a bad spark plug. New Spark Plug Resistance. 10,000 ohms. Chainsaw, lawn mower or weedeater won't start or spark plug has no spark? So, although you may have spark, it may not be adequate to jump the plug gap with the engine running. ... Good spark plug wires should measure less than what per foot of length? Think of it this way, how many ohms do you think it is when the spark jumps the plug gap under compression? Spark plug resistors operate in the range of about 5,000 ohms. Spark Plug Wires. It is for this reason that most racing plugs are non-resistor types. While this is below the generic range, these are a higher quality wire so the resistance is less, so as mentioned before, check your vehicle’s specifications or the spark plug wire manufacturer specifications. 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. To check, perform the following steps: Remove the spark plug wire from the engine. If the spark plug ignition cables are getting faulty, it will have a much higher than normal resistance which causes additional voltage to be generated by the ignition coil which causes excess heat. You can test all you want, but spark plug … Make sure the spark plug wire does not have an open circuit, and as a general rule, the resistance should not exceed 1,000 ohms per inch (but may be permissible by some O.E. For the record, it's a brand new spark plug with the correct gap. There’s not many technical articles about spark plug wires, and for years we’ve been relegated to finding whatever information that was out there in the form of advertisements from manufacturers or on the back of the spark plug wire box. 2) Spark plugs are very inexpensive to replace. This, in turn, melts the coil’s wire insulation causing the wires to break requiring a new ignition coil. there should be 3 terminals on the coil. Dry and Wet Fouling. 6,000 to 30,000. With the introduction of coil-on-plug ignition, there is no long wire that is needed to connect a coil to the spark plug.. On engines that are equipped with a distributor or a remote coil pack, spark plug wires are used to transfer the spark from the coil to the spark plug. Because of this, the tool provides an accurate measurement of whether there’s enough spark to jump the plug … Its in the many-thousands of ohms. I'm fairly certain there is no spark though. Once a plug’s resistance gets higher than that, it’s time for a new plug. Reasons to check your spark plug first: 1) A bad spark plug is the main cause of poor engine performance. Touch one of the small pins where the wiring harness plugs in with the other meter lead. Generally they have positions for different levels of resistance, from 2 ohms to 200k ohms; choosing the right setting will give you a better idea of the right reading, which should be around 2000 ohms. Once you have read the resistance of the wire, divide that number by the length of the wire (inches) and this will give you the Ohms per inch. Not hard to differentiate between the two. This wire is about 2 feet long so we should be expecting about 1300 to 2500 ohms. I have been looking everywhere and I keep getting different answers on the internet. A 24-inch wire may come in between 7.50 and 9.00 ohms. With the way the 031 is constructed the wire lead to the plug boot is short, and the cover/handle makes it rather challenging to get the plug to the cylinder for grounding while still being able to see the electrode & look for spark. A good wire should have 1500 to 3500 ohms resistance. Technician B says that a defective pickup coil wire can cause an engine miss. I still have the '95 one here, as well as a spare newer coil pack. So if you test a 3-ft spark plug wire and get a reading of 10,000 ohms, all other 3-ft. wires should test the same. When removing spark plug wires, do not pull on the wire itself. Since resistor type plugs actually “resist” some of the spark energy, non-resistor type plugs actually deliver a more powerful spark. Champion Spark Plug Company’s Engineering Manual gives the nominal value for their resistor type of aviation spark plugs as 1000 - 1500 ohms (no +/- value is shown, but minus 400 and plus 1000 probably wouldn’t be … Compression Ratio: The higher the engine compression, the more voltage required to fire the plug, and the narrower the plug gap should be. The Society of Automotive Engineers suggests the maximum resistance should be 12,000 ohms-per-foot. As an example, if you have 4-feet of Super Stock 5000 or Street Fire wire, you should have an ohm reading of 2,000 ohms. For your vehicle here is what they have for specification. To do this successfully, they need to be covered in thick insulation to prevent high voltages jumping off the wire before it reaches the spark plug and a rubber boot at each end. To check the resistance of the wires, use a multi-meter to test the resistance (Ohms) of the leads. also check the sparkplugs for a fouled out condition. Routine Maintenance: When to replace spark plug wires. How many Ohms should a good spark plug wire test? We are looking at 940 ohms. unplug the ignition wire connector from the coil. I wired in a newer (97, male coil) coil pack onto my car, a '95 that had a female coil stock. And remember the old spark plug adage: “Drop it Once, Drop it Twice” (the second drop is in the trash). Re: Spark Plug Wire Resistance reading I don't know personally, but zero"ish" for stranded wire and 5k ohms"ish" for resistance wire, obviously length dependent. Spray some water with a spray bottle as well around the wires to check for arching. I just found this stating that the wires should be 1,200-1,500 ohms per foot. Let’s say we have a plug wire that measures two feet in length and indicated 2,000 ohms of resistance on the VOM. Testing spark plug wires and diagnosing bad spark plug wires. Important, yet un-sexy. A shorter wire with a length of 12 inches may test out between 6.00 to 7.00 ohms and a longer wire of 30 inches may measure out between 9.00 and 11.00. Update: I found a video on youtube some guy said that per every foot of spark plug wire the typical wire has roughly 4-5 ohms. Learn how to test spark plug wires with a multimeter. True. But be aware that the resistance of automotive spark plug wires can vary from about 40 ohms/ft to 10,000 ohms/ft depending on application. References RPM: The higher the rpm's the less time the coil has to charge to break over voltage or complete saturation. Close inspection of the boots and terminals should also be checked. Take a better look at your meter, no offense intended. If you have the high-resistance wires, there is a chance your simple tester might not register continuity. 1-15 in.. 3000/10,000 ohms 15-25 in.. 4000/15,000 ohms 25-35 in.. 6000/20,000 ohms OVER 35 in.. 8000/25,000 ohms Also inspect insulation for any damage. If the firing end of a spark plug is brown or light gray, the condition can be judged to be good and the spark plug is functioning optimally. However, some OEMs have recommended different maximum resistances. A narrower spark plug gap will help high rpm stability. However, in most automotive applications, a resistor plug is required for proper vehicle operation. So if you find a wire with significantly less or more resistance, you know that it’s defective. You can also measure the resistance of each spark plug wire, but like coils, values may vary between wire brands. 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