Have a low speed misfire on the A bank of my 6 litre XJS. Marelli ignition. Once the rpm increases the engine smoothes out or this misfire is then disguised by the remaining cylinders operating.
Cannot see any obvious cause and have searched THE BOOK for a cause.
The car was fine when put away last winter. The gas was stabilized.
Rather suspect an injector that is sluggish as it has improved since running 3 bottles of sea foam through it.
Any ideas anybody
Get an inexpensive mechanics stethoscope at any local auto parts store, start up the engine, and listen carefully to each A bank fuel injector to make sure they are all making a very pronounced clicking sound at a regular frequency. Alternatively get a noid light and check that the injectors cause the noid light to flash. The fuel injector connectors and the wiring can get very brittle with time. I have had to remove and replace several broken plastic fuel injector connectors in my two Jaguar 5.3L V12 equipped cars over the past several years. I haven’t experienced any rodent damage in my Jaguars but others have posted about rodents chewing through engine bay wiring harnesses especially after the cars were stored away for the winter with resultant misfires.
Paul
If your test of the fuel injectors doesn’t reveal anything conclusive you should investigate the Marelli ignition components. First look at the engine while it is running parked in the dark to observe the spark plug wires and distributor cap to see if there are any sparks. Then remove the spark plug wires, spark plugs, cap and rotor to see if there is anything unusual and if the plugs are good and properly gapped. Unless you know when the ignition components were changed before, suspect everything. A six liter XJ-S would be approaching 25 years old now and any original ignition parts could be failing.
Paul