Hi everyone,

Since purchasing my V12 XJ-SC a couple of years ago, she has always been "hard to start". She always would eventually start, but it would take multiple attempts before she would kick over and catch.

In that time I have replaced all of the spark plugs, distributor cap, rotor, checked and oiled the distributor weights, new HT leads, and when in there, did all of he injector fuel hoses on the injector rail. While all of that work fixed a miss on one cylinder (due to a cracked spark plug), she remained hard to start.

So, I jumped into Grant Francis's "So Ya got a HE V12 that won't start" doc posted in our Forum (https://www.jaguarforums.com/forum/x...he-v12-178286/).

I've been doing a few minor things like checking electrical connections, cables, etc, and I read the piece about the Condensor inside the Ignition Amplifier (black box). Looking at mine, it looks in great condition, but I thought I may as well remove the condenser and then do a test to see if she would start. Key in, switch on ignition, jump out and turn the pedestal to confirm I still had the injectors triggering (Yes), back in the car, turn the key fully on and within 2 seconds she fired right up. Now I need to do more testing, but the initial result looks promising! Will test again tomorrow. A couple of pics below of my Ignition Amplifier and inside the Amplifier. Looks may be deceiving! Thanks Grant and team for these Forums. Just terrific information and sharing of experiences.

Ignition Amplifier

Inside the Ignition Amplifier before removing the Condensor

 

Well done.

Glad the Sticky was of use.

I removed that Lucas sticker also, its an Aussie thing, HA.

 

The black piece on the inside is an easy replacement. Its actually a GM AC/Delco part.

 

Hi everyone,
For those following along ... 24 hours later and I jumped back into the car this afternoon, turned the key and she started first go! I was actually really surprised! Has never started that easily in my couple of years of ownership!
Hoping this is a permanent fix, but I will continue to clean up wires and connections in the engine bay, change out fuel filter, etc, etc.
Always something to do on these magnificent V12 beasts, and thanks to everyone that contributes to keeping these wonderful cars running!
Happy motoring, everyone!

 

Accidentally stumbled across the same solution a couple months ago, I was only getting ~9v to the coil which turned out to be a short in the harness but along the way I removed the zener diode and 'condenser' which solved the slow cranking issue that I wasn't even concerned about at the time.. lol

 

Here are a few suggestions for repair of Lucas Ignition amplifier. Original Condenser and Diode are not available. see attached
New production Ignition GM Modules don't need the diode, GM never used secondary diode, but did upgrade the internals of the module.
You can mount (Radio interference condenser) out side the amplifier as GM did. GM put module inside distributor and condenser on the coil.
Rgds
David

 

DAvid
Are these modernised ones available for sale?

 

To close out this thread, 2 days after removing the condensor from the Ignition Amplifier, jumped into the car again today, turned the key and within 2-3 seconds, she started. It never started that easily in all the time I've owned her. I call that fixed! Happy motoring, everyone!

 

I run the MSD 88362 module with no zener diode, been in the car for ~4mo now without issues, can be found here: https://www.ebay.com/itm/194213216916

Supposedly it's modern components in the oem packaging for race cars that need to appear stock

 

Quote:

Originally Posted by Greg in France

DAvid
Are these modernised ones available for sale?

Any new production... avoid "New Old Stock"
1. ACDelco D1906 Professional Ignition Control Module or the equivalent, ( Amazon usually has the best price and a lot of turnover)
2. Ignition Control Module Delphi DS10071-11B1

3. I use the Petronix D72000 HEI 4-pin Module (with their .6 ohm coil and plugs gaped at .005" over book)
-Multiple sparks thru the entire RPM range.
-Integrated digital REV limiter with LED feedback for precise RPM setting.
-Adaptive dwell maintains peak energy throughout the entire RPM range, reducing misfires while improving engine performance.
-Peak current level is reached just prior to spark for maximum energy without the heat build-up, increasing coil performance and module reliability. (keeps the coil cool)
-Adjusts spark timing at higher RPMs to compensate for the inherent electronic delay.
-Senses startup and increases energy for quicker, easier starting.
-Legal in all 50 states and Canada. (C.A.R.B. E.O. #D-57-22)
-Adjustable rev limiter is preset to 5500 RPM. (from memory this is for a V8, so need to calculate for L6 or V12 application)
-12-month manufacturer's warranty
Rgds
David

 

Thank you David, this is really useful info.
I also need a bit of clarification, being electronically illiterate:
You mention in post 6 above that the latest GM amplfier modules do not need a diode to protect them. Is this referring to the Zener diode on the OEM unit?
In the attachment you posted, C2.pdf in post 6 above, are the newer internals explaine in the document something that the owner has to do, or are such units sold ready to go?
Does the Pertronix module you recommended also not need the zener diode?
Thanks in advance

 

Quote:

Originally Posted by Greg in France

Thank you David, this is really useful info.
I also need a bit of clarification, being electronically illiterate:
You mention in post 6 above that the latest GM amplfier modules do not need a diode to protect them. Is this referring to the Zener diode on the OEM unit?

Yes, the internal Petronix protection is upgraded and adequate.

PS: My spare Lucas Amplifier has the Delphi module and I did test it on the car. I can confirm the Lucas Amplifier with the Petronix module gives a noticeable smoother idle.
Rgds
David

 

Any write up in using that Pertronix part? Seems like a worthwhile modification

 

You can go to the Pertronix website for PDF instructions. I installed on a 1984 6 Cyl XJ6 S3 (EFI) with no problems. It is an exact fit, and came with silicone paste for install; and (a new emissions decal that goes next to your timing decal on the Hood for you 40 year old California car smog test). Clean old paste with Acetone (or similar), and install it in Lucas Amplifier (clean all corrosion found around bolt holes, as these are all part of the grounding points). Comes preset to 5500 RPM limit for a V-8, which I left alone as didn't want the rev-limit feature. On a V-12 you would need to up to RPM 9750 RPM (= 6500 RPM for V-12).
Tachometer worked as normal.

There is a factory note that the D72000 (Stage 111) units do not work with some modern aftermarket Fuel Injection Computers.
This because of the multiple sparks confusing the aftermarket EFI computers.
The Bosch/Lucas system ECU on Jaguars filters out the two rapid spark signal and treats it as one long spark signal with two peaks.

They have a Stage 11 unit without the dual spark, and is paired with a different ignition coil, that would be equivalent to the GM D1906 ignition module.

I installed new plugs, wires, cap and rotor. You will be going from a stock 35,000 volts to 45,000 + volt system, any weakness in old components will be compromised.

https://pertronixbrands.com/pages/contact-us See HEI ignition modules

Rgds
David

 

Originally Posted by Greg in France
Thank you David, this is really useful info.
I also need a bit of clarification, being electronically illiterate:
You mention in post 6 above that the latest GM amplfier modules do not need a diode to protect them. Is this referring to the Zener diode on the OEM unit?

Found my notes in older computer files.
The original Lucas AB14 GM Ignition module was specified with a MC3334 IC, it was a 400-volt rated MJ10012 type.
Lucas added the external 350-Volt Zener Clamping Diode for protection.

Later GM HEI Ignition modules used the MJ10014 Darlington unit, which is 600-Volt rated; this solved the problem.
New and aftermarket GM 4 pin ignition modules should not require the external power Zener Clamping Diode in the circuit.
Rgds
David