2007 4.2 XKR I have an issue with cylinder 7 registering a missfire , sometimes enough to trigger a eml light other times not . So far it has had full set of coil packs and plugs. 4 injectors replaced on R/H bank, R/H injector wiring loom replaced, and lastly engine ecu swapped and still it persists. Coil packs swapped and fault does not move. Reading live data missfire only registers at idle increase to around 1200 rpm and stops showing . Also usually once this is done it will sit at idle without registering any further missfires. Any help much appreciated

 

Have you done a compression test? You may have a goofy valve.

 

Compressions checked and all ok

 

Clean and check electrical connections and wiring for #7.

 

I'd also say to check ohms between each injector connection to ground and then to each other, compare them to other connectors. All should be very similar.

 

I have changed the r/h injector loom and checked the earth point at front of head. But that is still a good suggestion