XJ12 S2 Won't start
 

I have an XJ12 S2. It won't start, I think its something to do with the ignition system. I changed the coil and I think I may have wired it up wrong but I've tried all combinations and tried again with the original coil. The car was starting prior to this but would stall unexpectedly after driving it for little while, so someone suggested the coil may be stuffed. Anyone have any ideas on what could be wrong?

Oliver,

S2 V12

What year,

Carby?

Fuel Infected?

Huge difference in diagnostics, and which hundreds of pages of scribbles I have on them suckers.

Hi mate.
It's 1974. Carburettor engine with a Crane ignition system.

OK, plot thickens.

Do you have spark?
What Crane are you running, XR700, or XR3000.
Does the beast still have the vertical huge ballast on the RH side of the throttle pedestal?
Is the Tacho "jumping" slightly whilst cranking?
Where is the Crane box mounted?

Hi mate,

No there is no spark from the coil. I don't know what model Crane it is. Yes it has the huge ballast on the RH side of the throttle pedestal. The Tacho doesn't jump when cranking there is no movement. The Crane box is mounted at the back of the engine bay on the RH side.

Oliver

1) OK, dead system.
2) Should be a label on it somewhere, my bet is an XR700, but that is a pure guess.
3) OK. That ballast is fickle at best. I have a terminal schematic for that thing somewhere, and I will dig it out over the weekend.
4) OK, no pulse via that ballast, as yours has the tacho driven via that ballast, as apposed to any other system, where the tacho pulse is via the NEG (-) terminal of the Ign coil.
5) OK as long as that box is EARTHED well. I would "think" about moving it up front, top of rad support panel is where I place it, as that rear section is the HOTTEST area of the engine bay.

#1 test for now:

Ign ON, measure the volts at the POS (+) terminal of the coil. Should be somewhere around 7v. Now crank the beast, and note the volts, should be around 12v. This is a very basic test of the ballast and the system.

Next:

Trace the wire of the Crane that is the 12V Ign Feed Power wire, RED is its colour, and ensure it is NOT connected to the POS (+) of the coil. That is sooooooo common, and will only supply that box with 7v +/- and that is not enough to get the thing excited. The fitting instructions show that wire attached to the coil +ver terminal, and ALL that I have installed that way, a VERY long time ago, do NOT work until a GOOD 12v Ign ON volts is applied.

My copy of the installation booklet is attached just incase, BUT beware what I said above about that RED wire.