Hello out there! I just picked up a 1984 Jaguar XJS with the lucas ce ignition system. It was stored for about 5 years and the owner passed away recently. His widow had a shop try briefly to get it running. They put a new fuel pump in it and a new ignition module in the amp box. I bought the car not running and am struggling with a no spark issue. I have no spark out of the coil at all. I have verified battery voltage at the positive terminal of the coil when cranking, pickup coil connector resistance in acceptable range (3.56), proper coil resistance (.01), replaced ignition module again just in case, used a delco d1906. Pulled the cap and verified pickup coil gap. Cap and rotor look normal, cap carbon brush is present. What am I missing, why can't I get sparks to fly? One other thing, the amplifier box gets warm, pretty sure that isn't normal? Please give me a hand with this, would like to bring this v12 back to life!

 

Forgot, I do that, hence the edit.

Welcome to the real world of motoring.

Based on what you have done.

It sounds like the coil/s are internally shorting.

I would be disconnecting the 2 wires that feed the front coil and try again.

Using an OHM meter test the "main" coil, with ALL wires disconnected. You are looking for approx 1.2ohms.

Age is an issue now with a lot of these items.

The heating of the amp is not normal, and that is what is indicating a shorting coil.

 

Thanks for the welcome, I'm excited to get this thing back to it's former v12 glory! I forgot to mention that I replaced the primary coil already as well. I did measure resistance with all wires pulled and it was .1 ohms I think? Slept since then... Resistance was the same on the old one I removed though. Have not checked the secondary coil yet. Makes sense that the amp is heating up if a coil is shorting though. Will have a look as soon as I can. Thanks!

 

Installed a duralast C877 coil. Spec says primary resistance is between .7 and 1.4.

 

I replaced both my coils with one of the new recommended low impedance ones. Ignition Coil - DAC6093 | Jaguar XJ6-XJ12 69-87, Jaguar XJS | Jaguar | British Parts UK works well and gets rid of the second coil behind the grill and all the wiring. I think that like most V12s of that vintage the wiring is probably and most likely simply cooked, check your wiring around the V. I would replace both coils with the single one, use a simple light tester to check wiring both positive and negative(earth) to check they are not shorted and go from there.
If your getting power to the coil no reason why it shouldn't throw a spark unless your dizzy has got a problem. Spend a few dollars change your rotor and cap, your leads could also be shot, if still no go at least you can rule out all the above. Its a matter of deduction
Good Luck

 

I have been reading through a bunch of old posts on no spark issues but I am stumped. Seems that there are some much more experienced Jaguar wrenches than me, and I could use some more advise. It appears that my Ignition amplifier is grounding. I removed the condenser and tried again with a different ignition module with the same result. If I remove the amplifier connections then coil voltage is battery volts on + and -, if the ampifier leads are connected then I have 10 volts on coil + and 3 volts at coil -. I have replaced the ignition module twice now and have checked all wires for any shorts and have found nothing. Diodes for tach and efi trigger wires seem fine, one is 10 ohms and the other is 6. What could be making the amplifier ground out like that? How do you check the zener to verify it's good and would it have this affect? I have 3.5k ohms at pickup coil connector so it seems ok. Please tell me what I'm missing!

 

Have you examined the shielded wire that comes off the amp?

Cheers
DD

 

It appears to be intact, what should I be looking for?

 

I have never seen a Zenor dead, maybe lucky, dunno.

Try disconnecting the Zenor, BUT, make sure ALL the spark plug wires are intact/connected, or the module may/will die.

Use your volt meter, and connect it TO the +ve of the coil, and note 12v at ign ON, then go to crank position, and ensure you still got about 12v during that cranking. The electrical section of the ignition switch is prone to dropping connection when going to START, and hence you are cranking OK, but have lost the 12v IGN voltage.

 

I checked and I do have 12 volts when cranking. Amp / module is definitely grounded. Not sure how I have managed to fry 3 modules in such short order. I guess I better get another one and hope for the best. All plug leads seem to be in good shape and have nice tight connections.

 

Grant explains it well, better than I can, in various posts in this thread

https://www.jaguarforums.com/forum/x...g-97458/page3/

Cheers
DD

 

This is concerning, so here goes.

I have not replaced that many modules in ALL the V12's I have owned combined.

The shielded wire from that module would reek havoc if the "shielding" was making contact with the module wiring/connections itself. That wire supplies an ignition pulse TO the ECU for fuel injection operation, and has NOTHING to do with spark or lack of.

Some thoughts I have at the moment.

The small wiring loom (2 wires) coming FROM the distributor and travels TO the amp, has a connector in it at "about" 3B spark plug region. Check the integrity of that connection. ALSO, those 2 wires are known to break INSIDE the rubber plug at the exit point of the distributor. This will cease pulse TO the amp, so NO trigger action of the amp = NO spark.

Still NOTHING to do with frying modules. That still eludes me.

I have an Ignition system wiring drawing somewhere???, and when I find it I will post it here.

 

Here ya go.

Pretty self explanatory.

That dreaded "shielded wire" plugs into the wire wth the "14" noted, and is generally a protected spade connection. That means teh "shielding" is a long way from teh amp in the real world.

I also would be seriously checking the engine earth strap fiasco that navigates the LH engine mount. It is really British engineering that alcks the real world integrity. I run a seperate single earth cable from the engine block to a chassis bolt (usually the rear most bolt of the LH "V" mount).

That earth cable not doing its job could be contributing to the module issues??.

V12 ignition diagram.pdf

 

I am thinking also you may have an earth issue, it doesn't take much a bit of rust on the connection and its gone. Have you got just a basic 12v light circuit tester? If not buy one probably the best $3.00 you will ever spend, great for checking connections and making sure you are actually getting the power to where its needed.
Auto Circuit Tester 6V 12V 24 Volts Voltage Gauge CAR Test Voltmeter Light Bulb | eBay
Multi meters can fool you. I had the problem with my bobcat it had a cut in a cable and corrosion set in, but the meter showed 12v, but when tested with the light it showed no connection, it had just enough wire left to give voltage but couldn't carry the current, Cooked wiring will also do this and I am pretty sure that you will find lots of nice char grilled wires in the valley of that motor.
Good Luck

 

Well I did some more digging and found the shielded wire for the efi trigger. I originally thought the shielded wire mentioned earlier was the one that attaches to the amp and goes to the pickup coil harness. I soldered a wire to the shielding and ran the wire to the ignition amp mounting bolt. Is this right? I wiggled the wires at the pickup coil connector and have no issues there. Measures a consistent 3.5K ohms. Everything is good until I connect the wire from the the ignition module to coil -. As soon as I do that the module / amplifier grounds. This seems more difficult than it should be. I am missing something obvious, just can't pinpoint it. Any ides?

 

I am pretty sure that the woven shield should NOT be grounded at the engine end. The inner wire should be connected to the wire from the amp, but the shield must be well insulated from it and everything else and touching nothing. There IS a wire that is earthed at the RH amp mounting bolt, but it is NOT the shielded outer of the wire to the ECU. It is an earth that comes out of the amp itself.
Greg

 

Hope I don't confuse things further but I took a picture of mine and I will detail where each wire goes.
amp_zpse460848b.jpg?t=1400590129
Starting at the top there is a white plug with 4 wires the one on the left white/purple looks like goes under the throttle linkage to the loom, the two middle wires go to your coil one positive and the other negative on the coil, not sure on the order , the wire on the right again white/purple goes again to the loom but closer to the injectors on that side.
On the side of the Amp are two wires blue and a red the blue is negative the red positive and the shielding around them goes to an earth on the manifold nowhere near the amp. these wires go the the distributor make sure that the shielding on the other side of this cable is capped off and not grounded, shielding should be grounded from one side only.
Hope this helps.

 

Thanks for the pic Katoh. Mine is pretty close to the same but the shielded wire to the distributor is connected to the rear amp mounting bolt. Looks like I grounded the shielding on the ecu wire in error. I will fix that tonight after work and see if it clears things up. Thanks again for the advise and wish me luck!

 

Well, here I am again, no closer to an answer than I was. As soon as I hook the wire from amplifier to coil negative I get a voltage drop at coil positive (10.8 volts) and coil negative (3 volts) I replaced the ignition module yet again, dug through most of the wiring, checked continuity or resistance on anything I could find that involved the ignition system, fixed the ecu trigger wire shielding, I can find nothing out of the ordinary. I am probably going to try a used amp and if that doesn't work I might just light it on fire...

 

Oh you Buetty, a Jag bonfire I'll bring the marshmallows!
Ok seriously now, I'm a little out of thoughts and ideas, its a shame your so far off as I have a spare amp here and some other bits and pieces you could try. It sound's more and more that your Amp is shorted somewhere, have you taken it off and looked within it? I'm not much of an electronics person so don't know where to start but if something has black smoke smears on it I know its burnt.
Sorry I can't help further.