Nice expensive little problem here...

The Lucas ignition amplifier box that sits on top of the intake on an '89 XJS ... I've killed three of them now in about 5 minutes time.

Burned the original factory one, then put a replacement on and burned that one (using the GM part that makes up the innards of the box), then replaced it and burned the third one. Something is shorting it out.

What could cause that? Bad distributor? And can that box be replaced with anything else (like an aftermarket MSD ignition box, etc.)?

Jess

 

The GM ones are the best, so something is taking it down. I'd try replacing the coil, make sure it's the proper low resistance (0.5 ohm primary) type of coil.

When you installed the module did you use the heat conducting paste on the back? That is important, as heat will kill a module. Is it also grounded?

 

My findings with too many of these beasts.

1) Coil is too high resistance. You got 2 coils, and with them paired, as made in Coventry, should have ABOUT 0.7 ish Ohms across the +vw and -ve terminal with ALL other sire NOT connected.
That GM module will tolerate ABOUT 1.0 ohms without issues.
2) The HT lead, all 13 of them, are OLD, and the resistance is way off the scale. About a 5 year life in a V12 engine bay.
3) Spark Plugs are either wrong spec, wrong gap, or OLD.
4) Engine Earth strap is broken, missing, whatever.
5) The carbon brush, up inside the dizzy cap, has fallen out, had a few of them, or worn down, RARE, so the coil CANNOT dump its energy, so the GM thingy gets belted, simple.
6) The actual Earth of that Box to the manifold is not good. I moved all my HE modules out the from of the radiator too many years ago, and never touched them since.

 

Dead short inside the unit?

 

Diode or Radio Interference Condenser are common short to ground failures. Ignition will work with both disconnected


Rgds
David