Skimmed through my repair book and searched the web, couldnt find it.

Can anyone tell me the firing order of the injectors on the XJS from TDC?

 

I am not aware of sequential firing of the injectors on the HE 5.3.

Now the memory bit, so look out, I may be fuzzy here. Quote me at YOUR peril.

They are wired in 4 groups of 3, and fire twice for each revolution of the engine and that is all 12. Being as the engine is "port injection" as apposed to "direct injection", that "squirt/s" sits behind the inlet valve and is drawn in at the crack of that valve.

I have never come across a timing sequence for the fuel side, only the ignition.

Now, the 6ltr, real late units as in X300 that have Nippon Denso engine management "may" have sequential" injection firing. I know my X300 AJ16 also with Nippon EM does have sequential injection firing.

 

I've wondered for quite a while why they did this. Doesn't the fuel pool on top of the valve when the injector fires with the valve closed? Wouldn't gas mileage be better if it were only firing when valve was open? Seems you could run a larger injector with better economy if they were sequential?