XJ6 Series 3 - Engine Misfires Under Load.
 

Hello folks,


I'm looking for some assistance with my 1985 4.2 Series 3 Sovereign. Engine runs and idles perfectly until at operating temperature at which point it develops a misfire or falters badly under load.


The misfire occurs when at low revs, particularly bad when moving off from a complete stop like traffic lights. The engine coughs and splutters and the throttle has to be caressed so momentum can be gathered. Once rpm reaches around the 2000 mark, the engine appears to clear itself and operates fine until another stop/start or cornering procedure.


I have a new ignition coil, rotor and distributor cap. New spark plugs, newish HT leads and all new vacuum hoses. The ECU, AFM and ignition amplifier thing are all known units to be working okay.


What am I missing, or where should I start looking next? The fact that it doesn't misfire or hesitate when cold must be a clue of some sort. Could it be over-fuelling?


Any assistance would be greatly appreciated.


Cheers.

Well, one thing that happens when the engine is cold is the fuel mixture is fattened up. This 'cold enrichment' tapers off as the engine warms up and is all done by the time the coolant hits 75ºC or so.

Your symptoms sound, off hand, like lack of fuel....the condition being masked when cold by the cold enrichment phase

Lack of fuel pressure or (very) dirty injectors are a couple possibilities

Cheers
DD