Jaguar Repair: 1985 xjs 3.6, fuel pressure gauge, air flow meter

Question
Hi
Howard, before we start I wanted to thank you for taking
the time to look at my question.
I have a 1985 jaguar xjs
fitted with LPG it runs on lpg but not on petrol i have isolated all of the LPG side of it just to be on petrol now it fires starts  about 2 seconds worth then stops.
Then i took out the injector ramp unplugged the coil for safety and the injectors spray but not always the same amount of fuel
i am sure you can help
Thanks and Kind regards Tony

Answer
Hi Tony,

I have never worked on the 3.6 but will try to help. You already know that the problem is fuel so you first need to put a fuel pressure gauge on the fuel line and watch the fuel pressure when trying to run it on gasoline. If it maintains 30+ PSI pressure when failing you have eliminated fuel supply as a fault. Next you need to check the power side of the injector wires at the time of failure to see if power supply is at fault. If it maintains power on the Power side of the injector wire then you have eliminated power as a possible failure.

Next, Do all injectors fail when you see them fail? or do only some fail? The injectors fire in groups. Power should be supplied at all times and the ECU grounds the injectors in groups. The time duration that the injectors are grounded is measured in milliseconds and that time is what controls fuel mixture. The injectors are not fired specifically when the intake valves are open and fires two times per cylinder firing.

Which injection system does this 3.6 have? Does it have a air mass meter or a air flow meter. The air flow meter is a large pie shaped air flow meter with a flap inside. It is not that important at this time.

Let me know,  

Howard