Metal ring under and inside where the mounting screw is the ground. Also a ground wire from alum plate to body. Conductive paste is not in the equation, conductive or otherwise.
Thanks exMBman, that makes the most sense to me also and that is definitely a good ground.
Robin, I agree, this has been cleaned and polished with new thermal past applied.
I believe this trouble shooting matrix eliminates the CPS as a possible culprit in the No Spark issue. The resistance measured 1.37k OHMS and Resistance to ground measured 0.L m OHMS. I wasnât sure about what the 0.L m meant so I did an online search and found this: âWhen measuring between any terminal to Ground, you always want to see OL. This means that there is no path for current to flow to groundâ.
No Spark Summary and Solution
Well itâs been a long thread to finally get to the heart of the issue. I canât tell you how many hours I have spent reading post, checking components, running down wires and trying to decipher wiring schematics in order to resolve the No Spark issue on my â94 VDP.
I would be completely remiss if I didnât acknowledge all the support and suggestions received here on the JagLovers forum, what a great bunch of guys, really, thank you all. I also want to acknowledge a couple of forum guys who went above and beyond what would normally be expected to help resolve the issue. My heartfelt thanks to Grooveman and Mike Stone, and a special thanks to Mikeâs brother Mark, who is not a forum member and doesnât even own a Jag, but got involved at Mikeâs request because of his expertise with wiring schematics. At my last post #184 I had really exhausted everything I could think of and was at a dead end, I really had no place else to look and I still had No Spark.
There are four major components that work together to produce spark, the CPS (Crankshaft Position Sensor, ECM (Engine Control Module), IA (Ignition Amplifier aka Ignition Module) and the IC (Ignition Coil). Although I had purchased a new coil and used but purported good replacements for the CPS, ECM & IA there was a lingering question as to the working condition of the used parts. In other words, were the used parts really in good working condition or was I just replacing one bad part with another bad part?
It was here that Grooveman sent me an email suggested that I might find someone local with a â94 VDP that I could persuade to let me swap out each of my original components on their Jag to see which component was bad, if any. I replied to Grooveman that the thought had never crossed my mind, and while I thought it was a great idea, that was not something I would feel comfortable asking another Jag owner. You can imagine my surprise when I received an email from another forum member with a â94 VDP offering to test my parts on his Jag if I would send them to him (he was out of state). Of course, I agreed and was extremely grateful for the offer (this had Groovemanâs fingerprints all over it). As it turns out testing each part individually and then in unison they all checked good.
After receiving my components back and installing them I still had no spark. This left me back at No Spark and out of ideas and places to look. It was then I got a call from Mike Stone and his brother Mark, they asked if I had a few minutes to run some test and of course I was delighted to hear from them and to run any test they wish. Mark had been studying the wire schematics and wanted me to pull the Ignition On relay and manually jump across 30/87 terminals in the base, in other words make the connection the relay would normally make. I did this and checked for spark at the HT tower of the coil, not only did I have spark, I had strong spark. I installed the HT lead back in the coil leaving the jumper wire in place at the relay base. Cranked the engine and SHAZAM it fired right up. BAD RELAY.
ISSUE RESOLVED: Long, long story short, it all boiled down to a BAD Ignition On RELAY. The problem was intermittent, early on I checked the relays and they checked good. As reported in this thread there was a couple of times the Jag started and ran fine for a couple of days, then just quit for no apparent reason.
Had I taken abercanadianâs (Larry) advice back at post #15 I would have saved myself and everyone elseâs time. That said, Iâm not a fan of replacing parts without knowing the part is bad. On the plus side I know more about my Jag and what makes it tick then ever before and made some really great friends in the process.
In closing, I canât express my appreciation for this forum and its members enough, THANK YOU ALL.
Jag.Man, thanks for the kind words - Iâm glad we were able to be of help and Mark (my brother), who was off work convalescing following knee surgery, was glad to have this challenge / learning experience to occupy his time. Through his perusal of the J-L forum whilst âboning upâ on the issue and researching potential problems, he was amazed at what a close community of like-minded folks we have here. Very special.
The main takeaway for me from this experience is that although a relay may seem to test good (i.e. you get voltage out of it when you should) the relay may not be able to pass the requisite amount of current for the task at hand. Mark explained to me he sees this occasionally with equipment he services (he is an electronics maintenance tech at a local hospital) and it is presumed to be because the relay contacts are burned and/or oxidized. Note the pictures Jag.Man provided from his âautopsyâ of his bad relay. At the end of the day, the mission was accomplished - keeping another XJ40 running and on the road!
Reading Grooveâs âsuccessâ post yesterday with your âthanks for help with no-start issueâ bit, I wondered what had happened to your starting issue and if you ever got the damn thing running again âŚand indeed you did get going again!
Great news and BTW had to scroll way back to post 15 to see what the heck it was that I advised! 
Oh yeah, those damn Hella blue relays again âŚ
Glad all is well (although I have to admit I missed reading the continuing BAFFLING saga) 
Onward!!
Larry, good to hear from you and thanks again for your contribution. The Jag is running great again. The truth is I really needed to know for certain that the issue was fixed so I didnât have to wonder if it was going to start. I can now take her out of town on a road trip with confidence knowing the issue is resolved. If you ever get to Arizona, look me up.
Letâs hear it for the Stone Brothers, an awesome dual.
Mike your take-away is exactly right. When testing relays there are three (3) test to run:
Apply power to terminal 86 and ground to 85, listen for âclickâ
With power applied check across terminals 30/87 with multi-meter for voltage
And most important, with power applied check across terminals 30/87 for resistance.
Time for Mark to get a Jaguar 
Joe, Iâm so glad that you finally found the source of the problem. I KNEW 
all along itâs gonna be and easy fix. So we learned something new about these relays. The clicking sound is not enough to determinate the overall condition of the relay. Itâs strongly recommended to replace all relays with sealed ones. I would do that if I were you plus if I remember correctly I suggested to open up all the relay modules and fuse boxes and check their soldering joints and reflow them if necessary. Then the electrical system will be set for a long time.
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Thanks Joe77, I have replaced all the relays with the Hella Sealed units and in the process of trouble shooting I did open up the relay modules under the passenger side foot well and checked them. I have not removed the fuse boxes to check them. Thanks so much for your support and contribution to this thread, you are a valuable resource to this forum.
This is also very relevant to the relays in the widow packs, had me fooled for a while until I worked that one out.
This TSB has some good practical info. It occurs to me that to avoid problems resulting from excessive probe insertion (YIKES!):
Perhaps one should keep a couple of Lucar terminals with short pigtails handy. As suggested in the TSB they can be used to check the fit (tightness) of the female terminals in the relay base:
Once inserted the terminal would provide a contact point that would avoid, in fact prohibit, excessive probe insertion.
Well here it is, 5 years later from when this post was started and I wanted to take the time to let everyone know that Yes, I still have my '94 VDP and it is still running GREAT.
The only other issue I have had was with the Sun/Moon roof motor and as always Mike Stone jumped in to help. It turned out to be a broken gear inside the sliding roof motor. I was fortunate to fine a used but good working unit on line, however, as these cars age, 30 years old now, it gets harder to find replacement parts for them.
Again, my undying gratitude to all the members of the forum for their continued support.
Thanks for the kind word. And here is my update: I believe 3D printing some of these parts may be key to keeping our long-of-tooth Jags on the road. I have not developed that capability myself (not yet, anyway) but I have a former co-worker who has. Jag.Man was kind enough to send me his broken sunroof motor/drive assembly which I passed on to Bob, my former co-worker. Bob did 3D print a prototype gear which initially worked but quickly failed (as Bob had suggested it likely would) because of the material used. He has sourced some nylon material and will print a gear for testing. Bob is still gainfully employed and is incredibly busy so is doing this on an âas-canâ basis. I will report again when there are further developments.
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Mike, good information, thanks for the update.
Use âfriendly plasticâ to create gears or any nylon parts that have to be tough. It has to be press molded, but melts in boiling water and remains pliable until it cools.
Broken gear teeth can be restored with pins, baking soda and Krazy Glue, check out youtube.