Sensitive Question
 

Utter novice, wondering where on a 1985 Series III engine I find the various sensors for the EFI?
one ratty broken oxygen 3 wire sensor perched at the junction of the cross bars under the bonnet, but no sign of any others (excusing the air flow unit).
where would i expect to find the ones (2?) that measure exhaust and HOW does this data make it way back to the ECU in the boot, i.e what wires where...

on the opposite side of the engine, at the intake manifold, you have all the other sensors and wiring

You have two sensors that provide the main input to the EFI, (1) the Mass Air Flow sensor (MAF), a rather large flap-valve box between the air cleaner and the U-bend to the inlet manifold, and (2) the engine temperature sensor atop the water rail on the inlet manifold. The MAF also contains the inlet air temperature sensor that acts as a trimming input. For US cars you have exhaust oxygen sensors too in the exhaust side, again these just trim the two main inputs.

Have a read -

Fuel injection and the Jaguar XJ6 4.2 Series 3 / AJ6 Engineering

This is a fascinating website and I hope it remains on-line. Other thing is that the EFI system in your car is totally analogue, as digital EFI came after the Series 3 had left production.

~ thanks

the sensors sound less complex than i expected from what you say, i have a rogue 3wire sensor in a strange position about the engine but it is connected to nothing and is obviously an after market add on with no obvious purchase (maybe engine temperature?)
while the MAF speaks for itself on sight I am less clear how to locate the "rather large flap-valve box between the air cleaner and the U-bend to the inlet manifold" to check it is all intact, just cant picture it when i look at the engine.

Here's a pic of my old Ser III. Maybe it'll help you visualize the layout?

Cheers
DD

cheers for that,
i see no sign of the rogue sensor i found so i expect it was an after market add on and might not be required at all.
my engine looks almost exactly the same, but i have spotted he absence of the rube at the end of the air filter cylinder. yours has an exit tube of some sort which mine is missing.