Hi Jagman, You must be getting pretty frustrated ! I hope Grooveman can give you some help when you contact him. You have checked or replaced every component I can think of regarding no spark. I’m guessing here but maybe it’s a cracked solder joint in the board where the EMS relay is situated.
Have you turned the engine over with the distributor cap removed to make sure the rotor arm actually spins ? I’ve never had the problem with my Jag but I’ve had two different cars in the past ( distant past !) where the distributor drive broke both caused by a sheared pin on a drive gear.
I know you have replaced the rotor arm, but I have read many times of new replacements turning out to be faulty, there was a whole batch here in the UK from one supplier that either failed after only a few miles or failed to work at all, apparently they were shorting out on the rotor shaft, the quick test was to put a dab of grease inside the rotor arm before pressing it down onto the shaft, if the spark returned it proved the arm was faulty and shorting out.
Casso, you could be right about a crack on the printed circuit board in the EMS, I had that happen on the control module for the A/C. Sometimes it would run and sometimes it wouldn’t, turned out to be a crack in the solder. I have pulled the connectors (25 pin Yellow & Blue) on the ECU/EMS to check the connections and see if any of the wires were loose, everything was very clean checked out good.
There is no spark from the Coil so doesn’t matter what’s going on with the Distributor. If I had spark to the distributor and no spark to the plugs the problem could be in the distributor.
I am working with Grooveman and will keep everyone posted on the progress and hopefully the solution as we go. Thanks again for continuing to help find a solution.
Another update: Grooveman pointed me to a thread with a lot of useful information ( [xj40] No start, CPS replaced still no rpm on tach ) and lead me to perform the following checks.
I tested resistance of the Red/Blue wires from the CPS at the ECU/EMS Yellow connector. They showed 1392 ohms, so no break in the wires running from the CPS to the ECU/EMS.
Checked ignition on power to ECU/EMS thru EMS main relay. Have power on pin 1 Yellow connector and pin 10, 14 & 22 on the Blue connector.
Pin 87 on the ECU/EMS main relay is always hot (not switched). With ignition on and relay removed, base shows 12v across pin 85 & 86. With the relay out and energized by applying ground to pin 85 and power to pin 86 you can hear the relay engage completing the connection between pin 87 & pin 30.
Just to be on the safe side I took the Ground terminals in the engine bay apart and cleaned them, however, they were not dirty or corroded.
That’'s all I have for now and still no spark.
OK guys, has everyone given up on finding a solution to this problem? I first posted on April 8th and have re posted updates of things I have tried. I have not seen any new suggestions since my last post on April 13. Admittedly I have not swapped out/replaced the ECU/EMS but I have checked the power to this unit and it appears to be good. I can’t believe there is not someone else who has experience the same issue and resolved it. I have read through a lot of post on this forum and it is clear there are a lot of Jag smart people on here. A few of those people are JaguarPete, Bryan N and many others too numerous to mention.
So to recap again, the problem is NO SPARK from the coil. The problem started intermittently where the Jag would quit running, like you turned the key off, for no apparent reason. Initially I thought it was due to my harmonic balancer going bad. After getting the harmonic balancer back the Jag started right up. I drove the Jag around for a couple of days and then no start. Fiddled around with it for a couple of days then all of a sudden it started, ran perfect. chalked it up to gremlins but didn’t trust it any more so just drove it around the neighborhood. Then got in to put it in the garage and no start and has not started since, that was over a month ago.
I took the time to read through Jim_Isbell_W5JAI’s post referenced below. Very long (78 reply’s) and very informative. ([xj40] Good thing theres no Dynamite in my tool box) While in Jim’s case he had spark, there were checks to be made in reference to other components.
A Jaguar mechanic friend of Grooveman thinks it’s the CPS but I just don’t believe the CPS is the problem. That said it may be the wiring from the CPS that’s the problem. Once I determine it was a no spark issue I checked to see if I was getting spark from the coil, I was not, so unlike Jim’s issue ref above that turned out to be a bad rotor I’m not getting any spark to the distributor therefore the issue has nothing to do with the distributor, rotor, plug wires or plugs.
I have a new coil, I’ve tried another known good Ignition Amplifier, I’ve tried another known good CPS, I’ve check the ohms to the CPS from the Yellow connector at the ECU/EMS (1409) so there doesn’t seem to be a break in the Red & Blue wire from the CPS to the ECU/EMS. while checking the wires from the CPS I checked for a short from the Red wire to ground and it was good, however, when I checked the Blue wire I got tone when touching to ground. I’m not sure if this is normal. I also checked the clearence between the CPS and the harmonic balancer and it checks at .037"
I’ve checked the EMS Main Relay, the one on the engine bay passenger side firewall with the black base. Pin 87 on the ECU/EMS main relay is always hot (not switched). With ignition on and relay removed, base shows 12v across pin 85 & 86. With the relay out and energized by applying ground to pin 85 and power to pin 86 you can hear the relay engage completing the connection between pin 87 & pin 30. I’ve tried disconnecting the condenser attached to the + terminal on the coil and that made no difference. The grounds are all clean and the battery is fully charged.
What am I missing here? One of you guys has the answer, please share.
Happy Easter
Ok well I feel for you!
I’m probably not the guy with ‘the answer’ and maybe I’m being totally ignorant but does a coil actually spark, or just supply the oomph to create the spark?
I was under the impression that the make-and-break of the rotor in the cap sent a whack of electrons down the spark plug wire and to the plug and IT did the sparking?
I don’t mean to be offensive or rude plus I’m not an electrical expert by ANY means but you seem convinced that the coil has to ‘spark’ therefore problem MUST be upstream of the coil and all downstream components must be good.
Have you changed the cap and rotor yet? And you have 200 rpm on the rev counter while cranking, right?
Ok flame away, experts! 
Looking at the wiring diagram I see no connection from the blue wire to ground so that may be your problem. I checked my spare CPS (working when it was removed from the car) and there is no continuity between either the blue wire and the black (ground) wire or the red wire and the black wire. Have you checked the contacts in the yellow connector to the ECU? There is a black (ground) wire that is adjacent to the blue CPS wire in the wiring diagram but I don’t know whether the two are actually adjacent in the connector.
Can’t remember if we’ve covered this before and don’t have time to read all of your posts now, but … Have you swapped the ‘king lead’ from the coil to the distributor? If that lacks continuity then it could explain why you don’t get a spark from it to ground when cranking.
Bryan N (always seeking the simple solution! 
)
Larry, the coil has two internal circuits, a few winds of thick wires around thousands with a thin wire, so two coils in each other. The whole thing is bathed in oil on old cars.
The thick coil gets battery voltage and this creates a magnetic field. When the current is removed (the breaker, points open) this magnetic field collapses and that, for an instant, induces an enormous voltage (maybe 20-60kV) in the secondary (thin) coil. This finds its way out the center post and gets distributed via the rotor and jumps the plug to ground.
So, the timing is set by the instant the system removes (breaks) power to the coil shortly. The rotor just needs to point in roughly the right direction so it will contact the correct pin.
If the cps measures out and finds its way to the ecu, but the ecu doesn’t send a signal back then it must be the ecu. With that reasoning I’d get a large sheet of paper and trace every component until you have come close to the culprit.
The engine has good ground, right? You might be on track with the wiring, and if this fails you and you don’t know what else to do the ecu could be fried and any replacement off ebay is no loss; as you’ll be able to sell it on if it doesn’t cure anything 
David
Good Morning Larry, First off your post is NOT offensive or rude, there are no dumb questions or solutions. We don’t always know where we will find the answer and I always learn something from the interactions with members. So in response to your post, yes the coil does actually spark when held close to a ground while cranking the engine if everything is working correctly. If, as in my case, there is no spark present at the coil then everything down stream is irrelevant to solving the problem.
Thanks Mike, I am somewhat puzzled by the wiring from the female connector for the CPS at the front of the engine to the EMS Yellow connector. The wires from the CPS are Red, Blue & Black. The female connector that the CPS plugs into at the front of the engine has Red, Blue & White wires. At the Yellow connector on the EMS the Red wire is at pin 13 and the Blue wire is at pin 24 (see attached).
With the CPS unplugged at the front of the engine checking resistance across the Red & Blue wires gives a reading anywhere from 1390 to 1410ohms. If I plug the CPS back in and check the resistance across the Red & Blue at the Yellow connector at the EMS I get the same readings. So my logic says that the wires running from the front of the engine to the EMS are good and not broken or shorted.
Now here’s where it gets into an area I’m not clear about. With the CPS connector at the front of the engine disconnected, if I check for continuity between the female Red pin to ground there is none, but from the Blue pin and White pin to ground I get tone (this was a test suggested by Bryan N that I read in another post). The thing that has me puzzled is that the Red & Blue wires from the Yellow connector at the EMS seem to join together with a thick black wire and a thin White wire about 3" out of the Yellow connector (see photo).
I don’t understand this so I’m leaving it to the smarter guys to tell me if this is OK.
Hi Bryan, excellent question and one I forgot to mention among all the various checking I have done. Yes, I have swapped out the king lead from the coil to the distributor with a new one I had on the shelf without resolving the issue. I really do believe it is going to be something as simple as that to solve the issue. Thanks
Hi David, thanks for posting. I’m not clear how to check if the ECU/EMS is sending the signal back out to the Ignition Amplifier
From what you have tried so far I think the next step s going to have to be trying a replacement ECU.
Just to be sure you haven’t inadvertently reversed the battery connections at any point? BTDT and the ECU does not like it, take my word 
Thanks Robin for posting. I can positively say the battery connections have NEVER been reversed. I may have to sub-scum to buying an ECU just to eliminate it as a possibility, however, I’m not there yet.
Hi Jagman,
forgive me if I’m suggesting things you have already tried.
Have you got a 12V suppy to the + terminal on the coil ?
The Haynes manual has a procedure for checking the signal from the ECU back to the coil.
’ Using an LED type test light, backprobe the coil power lead (negative terminal ).
Remove the coil secondary wire and earth the terminal to the engine. have an assistant crank the engine and observe that the test light pulses on and off, if there is no flashing from the test light most likely the computer is damaged ’ and then it mentions having the ecu diagnosed at a dealers.
I’m assuming by backprobe they mean connecting the test light to the lead and touching the probe onto the terminal on the coil ? It seems to show that in the photo .
"
Thanks Casso, I’ve not seen that check before, exactly what I needed to know. I will report back as soon as I can check it out.
Hi Jagman, I think I should have mentioned that the ECU to coil test procedure in the Haynes is a long way through the section on ’ Ignition system check ’ and is assuming all the previous items mentioned such as the CPS, Ign relays etc have been tested and checked out as good BEFORE you can assume the ECU is faulty.
Another thing I would check would be the 12V supply to the + side of the coil while the assistant cranks the engine. If the 12V is present but then drops away during cranking the coil can’t make a spark.
Casso, you may be on to something. When I hook up the multi-meter to either the + or - terminals of the coil I have 12V +/-, while cranking the voltage drops to 8V +/-.
So what would cause the voltage to drop?
Bad battery? you could take it and have it tested,
But it cranks fine?
Bad voltage to coil possible.