Hi guys, i posted in the wrong area of the forum, i'll copy / paste it here as well,

Hi all, running the 5.0 SC motor, we've just done the timing chain, guides, tensioners, did not do the cam phasers though, and got the head rebuilt on the passenger side (Australia), after putting it all back together we were getting random misfire 5 & 6,
New spark plugs, Coilpacks, Injectors - same thing.
Disabled the aux belt so the superchargers out of the equation, and isn't throwing the knock sensors off and perhaps causing misfire - same thing. I am getting a slight knock in the SC, its bearings have 130,000kms on them. Couplers been replaced though in the snout.
Swapped cyl 1 & 2 plugs, coils + injectors into 5 & 6 using re-seal kits each time - same issue.

For some reason, the ECU is not firing 5 and 6. If we detach the loom clips for the injectors 5 & 6 we also get "injector circuit break" as well as "Random misfire". If we plug the loom clips back in, all we get is "random misfire", so this tells me the ECU is pulsing injectors in cyl 5 & 6 and its spraying fuel, just no spark.

I've ruled out;

• the SC knocking (coupler has been replaced),
• faulty cat or O2's, since its not the entire bank, just 2 cyl's
• knock sensor
• compression test was 120 + all cylinders so its not that
• timing was aligned using appropriate cam locks, timing tool, etc, and done by an ex Jag mechanic so its not timing related.
• head was rebuilt on that side by professionals, all new valves and seats, basically a brand new head.
• brand new genuine gaskets everywhere from Jag/LR.

Since posting this in the other section of the forum, today we tried;

Measured for impedence on the coilpack and injector looms to rule out the loom having breaks in the wires when the mechanic was folding/moving the loom out of the way during the timing-chains.
Measured for continuity from the ECU pins to the connectors on the coils/injectors, did a bunch of tests thanks to dads superioer knowledge in electrical engineering,

Turns out my ECU is somehow lowering the voltage to the coilpacks/injectors so its not firing either. once we unplug the loom from the ECU entirely, the short circuit disappears on the injector and coil side.. so something seems to be shorting within the ecu or between the ecu and coil/injectors of cyl 5 & 6.

 

Look at the signals on the coils and injectors with an oscilloscope. If signals are bad change the ECU, (you need to program to the VIN).If they are good check other things.....
Did you check cam clearances after head reassembly?