Ive got a 95 XJR 6 cylinder 150000 miles . It mis-fires at a steady speed but accelerates OK. Idle can dip to 500 rpm in gear but generally does'nt stall . I ve changed the plugs (twice) and bought a new coil which Ive swapped in and out with the old coils. No joy. When mis firing badly at say 2000 rpm it will pick up well after a slight hesitation. Any ideas???
Hmmm just a thought do the valves on your car have double springs? im not sure what rpm limits are needed for duel springs but if one of the duel springs were to be broken then you could maybe reach the natural resonance of the one remaining spring and then your valve wouldnt close properly. Dual springs are used to over come things by both springs having a different natural frequency and thus causing valve bounce where the valve doesnt close properly. Hey its only a thought allthough im not sure whether at 2000rpm that valve bounce would be a problem. On another thought if you've got access to a garage can you not at night in the dark run the car with the bonnet open and see if you can see any arcing or tracking of electicity around the dizzy or leads causing the missfire. Like i said only ideas
Jaguar X350 XJR ECU Remapped, Upper Pulley mod, Freeflow SS Exhaust, Nitrous / Jaguar X308 XJR