Hey guys, my 1990 jaguar xjs 5.3 with the marelli ignition has battery voltage to coils but no spark from coils. Could someone point me in the right direction to start with? Thanks.

 

Use Google and search something like "1990 Jaguar XJS crank position sensor specs resistance", or something like that. You want to try and find info on the at rest resistance on the front and back (bell housing) crank sensors. I would go looking so I could provide some better advise or suggestion but I'm at work now and can't. One of the 2 sensors controls the signal for spark.

There is also a vac line that comes off the back of the RH intake manifold. It's a hard plastic ORANGE line that runs into the car to the Marelli ignition module at the kick panel on the RH side in the RH foot well. See that it is not cracked or off of the spout on the intake manifold. You might want to remove the kick panel so you can access the Marelli ECU in the foot well and check the plug and harness.

Then, there are the ignition modules themselves on the upper radiator cross brace,,, I have NO idea how to test those.

Then, you'll of course need to inspect the wiring in the connectors to both coils. The wires can break away from the metal connector internally. Inside of the male plastic connector. Look closely.

​​​​​Then, the rotor, cap and,,,...

Are you getting them the infamous white coax wire...

 

Ok I’m sorry about my post being so vague. I’m getting battery voltage to the coils but nothing from the Ht lead on either coil to the distributor. I did continuity checks from coils to the PCMIs/ ICMs on the crossmember above the radiator. Everything checked ok. I did continuity checks from the ICMs to the ECU and all was good there. I don’t know how to test the ICMs or the ECU? That’s where I’m at now.

 

Like JayJagJay mentioned, the most common culprit for no ignition on a Marelli car is a failed Crank Position Sensor (or the wiring). There is an RPM sensor at the flywheel too, but it's almost always the crank position sensor that fails that prevents the ECU from computing spark. Sure there are a lot of other electrical checks you could make at the amps/wiring etc, but staying simple with the common culprit is the best advice I can give. CPS resistance is supposed to be around 700 to 850 Ohms but unless you test it with an oscilloscope, even that is not conclusive.

~Paul K.

 

Ok thank you! I’ll have a look and let you know how it goes. I appreciate it.

 

Hi charlestj8811

Start by cleaning any 'Crud' off the Front Crank Position Sensor

This Front CPS Sensor Triggers the Injectors and the Spark, while the Back one Monitors Engine RPM to the ECU

As has been already said, its nearly always the Front one that is the problem, where more often than not its the Gap that should be 018 to 0.042 and anything beyond 0.042 could be way too much and so in this case get the Gap between those two parameters

If you can't adjust the Gap and if the Gap is too wide, you may have to give the bracket a gentle Tap with a Hammer or even lengthen the holes a little bit with a small file

If none of that works you may have to take the Crank Position Sensor off the Car to Test it, which is well worth doing as they can be quite expensive to replace, though if the Crank Position Sensor dies for any reason at all this will literally cut the Engine just as if you had turned off the Ignition

Which is exactly what happened to me when driving down a dual carriageway at 70 MPH when one of the Belts broke and clobbered the CPS and stopped the Engine, which can be quite inconvenient, if you are in the process of Overtaking a Truck (ask me how I know or rather don't!)

You really need an Oscilloscope to Test the CPS but since most of us don't have one, at least the DVI Meter will give you a Clue

If none of that works get back and we'll try something else