[Richo]

Notwithstanding previous tongue in cheek comment, good on you for having a crack at CJ to get it fixed. But my own thoughts, you are probably pushing it uphill....
1. you stated it was outside of warranty period/milage. As i see it, the 100,000 warranty is the warranty, not 100,000 +/- 20,000.
2 the chip is a modification, which will increase power and hence stress on the motor. CJ have a reasonable case not to warranty on this basis. You installed the chip (ie modification), you wear the risks.
3. maybe as a side point, but nevertheless you have stated you were giving it grief at the time. 140+kmh overtaking with a trailer on the back (apart from the fact that it seems a bit foolish to me, but who am i to talk?) is no doubt stressing the engine.
4. the failure of the ecu/injector would appear to be the start of it, maybe the cause of it. Was it caused by the injector, or the chip?

Good luck, but maybe you should cut your losses, either go elsewhere (as suggested) for a rebuilt motor, or sell the car without engine.

Let us know how you go, interested to see outcome like many others on here.