I have a 1990 XJ-S V-12 with Marelli Ignition. Recently, I discovered that it had the classic problem of a burned through rotor that disabled the A-bank ignition system. It started and idled, but had no power. So, I pulled it into the garage.

I replaced the rotor and cap with new aftermarket ones. (I did not yet do the modification involving cutting off the nub on the distributor and filling up the bottom of the rotor with RTV.) I put it all back together and now it won't start at all--it just cranks. I've triple-checked the order of the spark plug wires and I do have 12V at the coils. I also checked the orientation of the rotor, in case I put it in backwards, but it doesn't appear that's even possible given the location of the bolt holes in the rotor.

I get one spark when I put the ignition in "run," but no spark as the engine cranks over (with an in-line spark tester at one of the coils)

Curiously, I have a new behavior--the starter runs on for 5-10 seconds after releasing the key from the "start" position (possibly just a coincidence--perhaps this was masked by the fact that it used to start?) Is something amiss with the ECU?

I will go through the full "no-start" procedure, but it is quite suspicious that the only change was the cap and rotor. It was a simple procedure. The only other wires involved with the "fix" were the two connectors to the cruise control--which I disconnected temporarily during the procedure.

Any ideas?

-joel

 

Check the coil king leads are connected correctly on the distributor cap. When I pulled my leads etc I mixed up the coil wires and it wouldn’t start.
Rob.

 

Thanks, Rob.

It is possible that I swapped the coil wires. Just to confirm, the top coil is for the "B" side and the bottom coil is for the "A" side, correct? My intuition would be the other way around, but I'm finding that this car is not always intuitive...

-joel

 

Just checked on my car. Top coil goes to B on the distributor cap. Bottom coil is A.
Rob.

 

Darn. I was hoping that was the fix. Alas, that is the way that I have them connected.
-joel

 

Are your modules up front connected correctly.?Quick check, you never know.

 

Solved! From what I can tell the problem was with the brittle insulation in the wiring harness. I had several places where the insulation broke and exposed bare copper--most significantly was the wire to the TDC sensor where it was touching ground. I fixed that and it started right up.

But WOW is that insulation fragile. I'm ready to pot the whole engine compartment in RTV!

-joel