Plug wire testing - Missing engine, odd response running or starting, cold vs hot -------------- Open the hood at night and see if there is visible arcing. Mist the wires with water from a spray bottle ( Use rubber Gloves) (add a little salt to make the water more conductive). Be sure you check the wires in TOTAL darkness, as crossfiring and arcing can be hard to see sometimes. Also, check it when the engine is warm, as it will be running leaner then. Checking resistance - Use an Ohmmeter - 1.5k per inch max resistance 30k ohms max per wire. Throw them away when they reach 10k ohms HOT. Check them while they are very hot (temperature). They may be just fine cold. Another way to test them on a Rainy day is spray them with WD40. It absorbs moisture and will idle and start better after spraying if they are bad. -------------Added 03 feb 2002 ---------- /////Is a simple continutiy test enough to tell if the wires are okay?///// -------------- To be considered good, ignition wires have to have an intact conductor, and good insulation as well. Older Studes may well have copper-core ignition wires, which can be checked out with a continuity tester. If replacement wires were used or if you are looking at a mid-to-late '50s or newer, it may have resistance-type ignition wires. They typically have resistance on the order of 10,000 ohms (10k). Could be from 2k to 20k, though. A bad wire would have resistance near infinity as checked on a multimeter. Even a $10 multimeter from Radio Shack would be OK for this test. Just use the R X10k or R x100K scale if available. A continuity test won't tell you if the insulation is breaking down. Try idling the car at night in a very dark place, and look for glows or sparks escaping from the wires, or pass a grounded wire like a jumper cable along the length of each wire, and see if it draws a spark. An ignition scope has a function to test "ignition reserve" that can clue you into bad wires, as well. Or just pass a calibrated finger along the wires. Wear a hard hat so you don't cut your scalp on the hood latch if you find a bad one. Gordon Richmond ----------------- I tried that and there is so much resistance, that all my wires had no continuity at all, even though the were all working. I have seen machines at NAPA stores that will test them, but I don't know if it was a marketing tool or not. ------------- Use an ohm meter Each length will be different, but you can tell if one or two is way way off. Flex the wires and watch to see if ohm reading changes around. throw out any that read far enough out of the ordinary. Throw out any that feels stiff in any areas. That may be the insulator deteriorating and no longer insulating. If the insulator covering is slick and shiny, it it is probably still doing it's job. The duller it gets, and the more the insulator ages toward chalkboard-porous, the more the car will act up on damp days, and misfire around puddles. small pores with embedded dust even when invisible, will make a good conductor when even only slightly damp. D L ---------- The above messages give good tips on checking the wires. Remember to "zero" out the meter before checking ohms rating of each individual wire. Otherwise a false reading will occur. The metallic core (copper wire) from past years will read a zero or no resistance and that is correct. Any minimal resistance shown will most likely be from corrosion at the terminal connection. Any breaks in the line will result in no movement of the meter, good connection will swing the needle across the scale. Early resistor core wire had a proclivity to breaking down due to heat and vibration and poor handling by a "mechanic". The cores have greatly improved over the years and are typically a kevlar/conductive latex(carbon impregnated) construction. These will start at 5-7000 ohms per foot (SAE) standard. So if your wire is two foot long it will measure 10-14,000 ohms when NEW. Old age and handling will take its toll and increase the readings. Wire wound suppression core is a mix between the two, conductive latex with a fine wire wound around the core. Ohms will be from 50 to 800 ohms per foot depending on manufacture. Possibility of some AM radio interference with this construction (static). Those who have purchased wires from RF(Studeman) will see a 300 ohm reading for example as they are a wire wound construction. Jackets (insulation) on the early wires was a Hypalon material and will stiffen and crack with age. Newer (mid 70's) construction used silicone in the exterior jackets. Cheaper wire sets available today will use various synthetics instead of silicone for economy. In addition some sets are made with only one jacket or layer of protection, the better have two. Always buy the quality sets, you will be happier in the long run. Sets bought from RF have a outer silicone jacket with a inner EPDM layer. Most spark plug wires will wear out due to internal/external heat and vibration, but poor handling will get then there faster. Grabbing and yanking in order to change plugs, distributor cap, clean or whatever will loosen up the crimped terminal connection faster than anything else. This will increase your resistance and cause your ignition system to work harder. Twist first to break loose the boot from the insulator and pull in a line parallel to the spark plug. Reach down far enough to be holding the terminal in the boot as you twist and pull off. Treat your wires with care for longer life. bscott@alltel.net ------------------------