Hi Fabian,
There is no need to fit a standalone engine ECU. The probable reason that your engine won't start is that your engine ECU is fitted with engine immobiliser software. This will prevent fuel injection, unless you fit the whole security system. I can provide you with a Jaguar production engine ECU hardware without immobiliser function. This will provide yuo with the same level of driveability as the original XJR6. I have provided many such engine ECUs over the years to other owners installing these engines into other Jaguar and non-Jaguar vehicles. I also reprogramme the ECUs to advance the ignition timing to provide more performance. If you happen to also be performing a auto to manual conversion, then I can also reprogramme the ECU for the change in transmission. Please email me directly (andystodart4@gmail.com).

 

On the X300 as designed there is an inertia / crash switch in the engine circuit that may be mis wired between the Series 2 and X300 conversion

 

Would you be able to remove the limiter from ecu?

 

I can increase the engine speed at which the rev limiter takes effect, but not technically remove it. However, as I see you are in the USA, I assume that your X306 is automatic, in which case the transmission will upshift before the speed reach the rev limiter, unless you use the J-gate to hold the gears down. The rev limiter in the manual cars is set to 5,950rpm. If I set the rev limiter any higher, there is a risk of overheating the crankshaft torsional vibration damper. Unless you change the cam timing, the engine won't make any more power, just by increasing the engine speed.