Ignition lead replacement
Some engines need special tools to replace ignition leads – boot pliers and spark plug boot pullers – to avoid damaging the boots. Leads should be replaced one at a time with the engine off and cold, after checking the set against the SENTECH catalogue drawing. Several sets for VW and Mercedes-Benz engines carry a higher risk of terminal damage during fitting and removal.
Replacing ignition leads with the right tools
In some cases, the right tools are needed to replace ignition leads correctly. These include pliers for pulling the lead boots (caps) off the spark plug insulators. Pliers of this kind are designed specially by vehicle manufacturers and are sold as special fitting tools for a given make of vehicle. Sometimes they are even part of the vehicle's tool kit – the owner's handbook will tell you. Modern tools for deep-seated spark plugs are also needed, as the spark plugs should be replaced at the same time as the leads.
The new ignition lead set must exactly match the criteria specified by the vehicle manufacturer. These are listed in the SENTECH catalogue; the most important are the make, engine capacity, year of manufacture and engine type. It is also worth comparing the "old" original leads with the technical drawing of the new ones, which is also included in the catalogue. If everything matches, you can start replacing the lead set. Using the data in the SENTECH catalogue ensures that the set meets the vehicle manufacturer's requirements.
Where the vehicle manufacturer specifies it, we recommend using the tools mentioned above, as they are essential for removing and fitting the leads correctly:
- spark plug boot puller
- pliers for hard-to-reach places
These tools are indispensable for replacing ignition leads properly, and they must be used to avoid mechanical damage to the boots through incorrect handling while fitting the new leads. For safety and correct fitting, ignition leads must only be replaced with the engine switched off and cold. Just before fitting, check the lead set description in the supplier's catalogue once more and compare the old leads with the new ones or with their dimensioned technical drawing. To avoid mistakes, replace the leads one at a time and in order.
Step-by-step replacement
Use special tools for the replacement. Never pull the boot with an unsuitable tool or, worse still, pull the lead itself, as this can permanently damage its connection with the terminal (contact end). First remove the lead from the spark plug, e.g. of cylinder 1, then disconnect its other end from the distributor cap or the ignition module. Next, choose the lead from the new set that is identical in length to the one removed and fit it in exactly the same mounting and routing points. The metal terminals must noticeably snap onto the spark plug terminal nut and into the coil tower or distributor cap socket, which you will hear as a distinctive click. If a terminal does not snap into place or the connection is loose, the terminal has been deformed by mistakes made during a poorly performed replacement.
As well as ensuring a proper connection of the metal contacts, make sure that not too much air is trapped under the rubber boots, as it expands with heat and can later push the lead off. Repeat the same procedure for each lead in the set. After fitting the last one, place all the leads in their holders, refit the covers and so on, to keep the lead set separate from the other engine components.
Sets with a higher risk of damage during fitting
The following sets (selected from the VW and Mercedes-Benz group) carry a higher risk of damage to the spark plug-side terminals during fitting and removal: 8083, 8137, 8138, 8246, 8424, 8456, 8457, 8465, 8467, 8542, 8546, 8579, 8597, 9001, 9025, 9026, 9034, 9062, 9076, 9077, 9081, 9083, 9097, 9100, 9110, 9115.