Jaguar Repair: jaguar xjs 3.6, air flow meter, jaguar xjs

Question
i have a problem with my jaguar xjs it is the early fuel injection system the one without the crankshaft sensor when i turn the ignition on the injectors pulse once but when i crank the engine over the injectors do not pulse ie the car isnt getting any fuel have changed the ecu fuel pumps injection relays basicly everything could you possibly help the car is a 1984 thanks

Answer
Hi Ian,

I am not familiar with the "S" with a 3.6 engine but all injection systems operate the same. They all pulse their injectors in a short time in milliseconds to control the fuel mixture and all use a signal from the ignition system to start injection. They all use something to meter the fuel according to the amount of air entering the engine and all alter mixture according to engine temp. Most of the other inputs to a ECU are just trimmers for minor adjustments like the air temp, O-2 censor etc.

First thing you need to do is to confirm that the engine itself is ok by spraying starting fluid into the intake to see if it will start and see if you can keep it running on starting fluid.

If you can do that, then put a "Noid" light on an injection wire and spin the engine over and see if you have a injection pulse light. (most auto parts store have a selection of different brand "Noid" lights and they are not expensive) (Yours should be a Lucas/Bosch)

If you don't get a flash, test both of the pins with a test light with the key on to confirm power. (the early Lucas/Bosch systems powered the injectors through a resistor pack)

If you did get a good flash, You need to test fuel pressure close to the injection rail. (30 to 42 PSI at the rail with the engine spinning, depending on which injection system this is.)
Does it have a pie shaped air flow meter? If so it is a "L" Jetronic system like the series III XJ-6.

If it started on starting fluid and you have no injection signal with a "Noid" light but do have power at the injectors, then you need a wiring diagram of that type of injection system.

With the diagram in front of you trace which wire is the signal called either ignition or engine speed censor at the ECU plug. I like to use a "Logic Probe" as they can test a mild signal without interrupting the signal. But you should be able to use a 12v test light in that test.

The ECU will not start grounding (pulsing) the injectors until it sees an ignition signal or a engine speed signal.

If it has all of that and still does not pulse the injectors, you need to take the diagram and confirm that all the power supplies to the ECU are powered (some systems use several power sources) and the ECU ground is a good ground.

Then if you still have not found the problem you will need to test each wire at the ECU to confirm that it is connected to each item that it is suppose to be connected to.

Most item will not shut the system down except some injection systems will if they loose the air flow meter or air mass meter (depending on which system it is)

I am familiar with the Ser III XJ-6 system with the pie shaped air flow meter and if it has that system let me know and I can supply you with a copy of a good wiring diagram.

If the original owners manual is still with the car, Jaguar was always good about supplying a injection diagram in with the paper work in the owners manual.

Howard