Although this problem is not common, it is an irritation for owners of the vehicles concerned. From our experience, after working with vehicle owners to solve this problem, we offer the following suggestions as to why this problem occurs: Boots or connectors not fully pushed on (and/or metal terminals inside not engaging): The most common cause. If you are fitting wires to an engine where it is almost impossible to easily reach the spark plugs or distributor and/or ignition coil/s, it is advisable to check the wires after the vehicle has run a few miles to ensure that boots and terminals are properly engaging and not just hanging there. An engine misfire will usually develop before boots or connectors actually pop off spark plugs (see specific instructions in Magnecor wire set boxes). Our best advice is not to rush the job. Before removing and re-fitting the wires, remove all engine components that need to be removed to properly access the wires. Installers often try to avoid removing other engine parts to access ignition wires, only to end up having to do the job over again because the wires can't really be fitted correctly without removing other engine components. Terminals inside flexible style spark plug boots have been spread by rocking boots from side-to-side to remove: A common cause after the removal and replacement of spark plug boots to reach spark plugs, although boots don't always completely pop off spark plugs. Unfortunately, all flexible silicone spark plug boots have a tendency to bond to the spark plug porcelain, and combined with terminals inside locking onto assorted size, shape and material spark plug tops (nuts, ferrules), it is sometimes almost impossible to easily remove the wires from difficult-to-reach spark plugs. The best approach seems to be carefully twisting the boot (with fingers as low as possible on the outside of the boot) and pulling the boot straight up and off the spark plug. Forcefully rocking on a boot to break the seal and disengage the terminal inside will inevitably spread the opening in the terminal and cause it to fit too loosely on the spark plug top when boot is re-fitted to the spark plug. Whenever possible, remove spark plug boots when the engine is cold, as spark plug tops expand into the terminals to lock even tighter when spark plugs are hot (or warm on some engines). With care, a spread terminal opening can sometimes be gently brought back into shape with long-nosed pliers. If the terminal mouth is too badly spread, the spring clip around the terminal (which has a punched dimple that drops into the middle of narrow section of the spark plug top) can be dislodged. If, after the terminal mouth has been brought back into shape the terminal won't noticeably click onto the spark plug, it is very likely the spring clip has been dislodged, and replacing the terminal will be necessary. If you are using Magnecor wires on a race engine, and are removing and replacing the spark plug wires frequently, you should take into account that you are putting many years of wear on the spark plug terminals in a short period of time (on most street-driven cars spark plug wires are removed, at best, only once a year). Unlike other spark plug wires used for racing, Magnecor wires can last many years on the same engine — therefore, you need to take special care to avoid damaging or deforming the spark plug terminals, which by the nature of their design and construction are small and easy to damage or deform if enough force is used. All Magnecor spark plug terminals are made from heavy gauge stainless steel and can usually withstand more abuse than normal terminals, but again, if enough force is used, any spark plug terminal can be damaged or deformed. If you do badly damage a terminal, we can usually repair the wire for you. Also, terminals can be purchased as spare parts from Magnecor. Also, some brand spark plugs tops that have had wires removed and replaced many times will score badly and create a loose connection. Spark plug connectors too full of silicone grease, a serious problem: A common cause on engines (particularly those of Japanese origin) which suffer the problem of moisture accumulating in spark plug holes. In the interests of water-proofing the spark plug connectors, well-meaning installers fill an extended spark plug connector with too much silicone dielectric grease, which can prevent the terminal inside from ever locking onto the spark plug top. Drivability problems caused by water in the spark plug holes can be cured (after water is removed) by applying a smear of silicone grease inside the connector bottom seals, or onto the base of the spark plug insulator. This will help prevent arcing when the moisture again accumulates — however, drivability problems will not be cured if a connector’s terminal cannot connect over a spark plug top because too much silicone grease is stuffed into the connector. Remember, grease can't be compressed, and if too much of it is stuffed into a connector, the metal terminal inside will never be able to grip the spark plug top and the connector will never connect properly to the spark plug. Too much grease stuffed into flexible rubber spark plug connectors will cause the same problem, but usually, the connector will only slide up on the spark plug, causing the engine to misfire. Distributor and/or ignition coil problems: Spark plug and coil wires can also pop off or out of distributor or ignition coil towers. The usual causes are similar to those that affect the spark plug ends of the wires including, in particular, stuffing too much silicone grease into the wire/s distributor and/or coil boots. In fact, we advise installers never to apply silicone dielectric grease inside a distributor or coil boot. If you need to insulate a distributor cap or ignition coil you should apply the silicone grease to the outside of the boot (where the boot meets the distributor cap or ignition coil) — distributor cap and ignition coil towers are tapered, and too much lubrication inside can cause boots to work their way up and off the towers on vehicles that experience considerable vibration. Some performance aftermarket distributor caps do not have a chamfer at top of the brass inserts into which the wires’ terminals will fit, so care needs to be taken to avoid the wire’s brass distributor terminals being caught on top edges of the inserts and becoming distorted (and too loose in the insert) if terminals are forcibly fitted. Usually, if a brass terminal does become distorted, bending it back to its original shape (compare with an un-distorted terminal on another wire) is all that’s required. However, too much bending on a brass terminal can cause it to break. Exhaust gas is blowing through a spark plug gasket (gaskets are used on some spark plugs to seal between the plug and the cylinder head) or through the body of the spark plug: A surprisingly common problem on vehicles using extended spark plug connectors to reach spark plugs in deep holes. The only cure is to replace the spark plug gaskets each time the plugs are removed and re-fitted, particularly if the vehicle manufacturer recommends replacing the gaskets. If you remove and replace your spark plugs regularly (for example, on a race engine) then you should pay particular attention to the condition of the spark plug gaskets. Also, spark plugs themselves have been known to leak around where the porcelain body seals into the metal base. Dark-colored marks left by leaking exhaust gases on the porcelain will indicate this problem — the only cure is to replace the spark plugs. In each case, above, the pressure of the exhaust gases can force the spark plug boot or spark plug connector of the spark plugs. Engine vibration, G-Force and torque twist: Engine vibration or shaking, if excessive, can cause ignition wires to disconnect, particularly if wires are stretched to fit onto spark plugs or into or over coil towers. Always make sure Magnecor Race Wires (the R-100 10mm version in particular, because of the extra weight) are properly loomed up and supported so that wires cannot swing and/or strike against nearby engine, body or suspension components, which can cause wires to be loosened or pulled from spark plugs, distributor cap and/or ignition coil/s during high G-Force cornering or braking. This is primarily due to the pure silicone construction of the jackets of Magnecor's 8.5mm and 10mm cables, which are much more flexible than other cables and do not get stiff over time. On Mazda rotary engines (in particular), allow enough slack to prevent the torque twist of the engine disconnecting wires from ignition coils. Spark plugs are too short or too high: An all-too-common problem with owners of Japanese origin engines fitting non-original spark plugs that too short or too high compared with the original plugs. Engines that use wires with extended spark plug connectors need to be fitted with spark plugs that are the same height as the original spark plugs to enable both the terminals inside the connectors to properly engage spark plug tops and properly position seals that cover the spark plug holes. Always compare different brand spark plug heights with original spark plugs before fitting them to the engine.