A misfire occurs when the fuel/air mixture in a cylinder does not ignite as it should. If misfires are frequent, then when the Land Rover is stationary the engine has a tendency to shake. Even the weight of a Series Land Rover is not sufficient to prevent a noticeable rocking of the vehicle as a result of such misfires. Misfires can occur in a single cylinder or intermittently across some or all of the cylinders, depending upon the cause of the problem. Note that 'backfires' as opposed to 'misfires' are accompanied by loud noises through the exhaust system (also the carburettor for petrol engines); these will be the topic of a December homepage.
There are some possible causes of misfiring in a standard Series Land Rover engine, regardless of whether the engine is petrol or diesel; these are related to the fuel/air mixture. If cylinder compression is insufficient then combustion may be incomplete or non existent. Causes of low compression can be a broken or sticking piston ring, sticking or wrongly timed valve operation or a leaking exhaust manifold joint.
Original Series Land Rover diesel engines
A sticking diesel injector could be the cause, but this would probably be accompanied by occasional backfiring also.
If the problem disappears when the engine has warmed up then it could be due to a faulty heater plug.
A partial blockage in the diesel return pipe could be the problem. If the pipe is removed and blown through to clear it then the fuel system will need bleeding of air.
The diesel distributor pump timing can cause the issue but this is unlikely unless the pump has been worked on recently.
Original Series Land Rover petrol engines
The first approach is to check each spark plug for condition - clean light brown coloration on the electrodes is ideal, with 0.025in - 0.030in gap (0.38mm - 0.43mm).
Removing one sparkplug lead whilst the engine is running (use insulated pliers) can cause little change in the engine misfire if the fault lies entirely with the plug/lead you have just removed. If, however, the misfire applies to several cylinders, then removing sparkplug leads in turn will not identify where the fault is.
One possible cause of a misfire in all cylinders is a faulty lead from the coil to the distributor. Similarly the coil itself could be faulty.
Other likely causes could be due to distributor faults such as faulty/dirty rotor arm, distributor cap contacts being burnt, contact points being pitted or a loose/worn distributor shaft.
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