There are two different routes for each fuel, Andrew - and it looks as if the petrol is not being adequately delivered, as Walter indeed suggests. Have you tried changing to the other (petrol) tank when the engine falter…?
I’m not well versed in Jaguar dual fuel set-up - but I assume that ECU is involved in metering both fuels according to pedal movement/air ingress. Basically; rpms/power are dependent on the amount of air going into the engine - which is controlled by the throttle, and measured by the AFM. And the amount of fuel adjusted accordingly by the ECU - unless LPG delivery is controlled by a separate agency…? Ie, delivered directly to the manifold rather than through the injectors?
So the amount of LPG is obviously delivered to spec, but petrol is not. Which may be restriction in petrol lines (including clogged main petrol filter), failing fuel pump or failing fuel pressure regulator…?
On the ignition side; the LPG may (arguably) be easier to ignite - and a weak spark may fail to ignite petrol? In either case; there are two white wires on coil ‘+’ - one from ign key, the other to the ign amplifier. And three wires on coil ‘-’; one white/black to ign amp, one white/black to the ECU (via the bullet connector mentioned by David).
And a white/slate blue going to the tacho - which at any time should slavishly show actual engine rpms. loss of ignition; the tach drops to ‘0’ and erratic tacho readings may imply an amplifier fault. The ignition system (coil, amplifier, distributor and plugs) is entirely self contained - independent on other components…
The ECU opens the injector once every engine revolution - on every third(!) ignition pulse. The best way to test this is to just listen to the injector (all simultaneously) ‘clacking’ during cranking. They are noisy, but you can use a ‘stethoscope’, a long scewdriver between your ear and an injector to amplify.
Not clacking; a (injector) test lamp (noid) can be connected between the two wires on a disconnected injector plug. With ign ‘on’, there is no light - while cranking; the lamp should flicker. Or with a digital voltmeter; showing '0’V with ign ‘on’ and ‘something’ while cranking. An analogue voltmeter will show '0’V and somewhere between 0 and 12V while cranking.
The cause of this is that one injector wire has constant power (ign ‘on’) - and the ECU briefly grounds the other wire to open the injector. Don’t bother about counting pulses - the ECU either operates the injectors - or it does not…
xj6 85 Sov Europe (UK/NZ)