The car will run PERFECTLY at times, and then it may not start, and then it will also idle way to low.

Replaced ECU, ignition amplifier, rewired pickup, new coil, new fuel pump and both regulators, battery, power resistor pack

I am getting a consistent spark, however when it is running perfectly it is blue, when it is not it is orange. Any ideas?

Submitted by bonnettoboot@e… on Sat, 03/17/2012 - 12:21

In the boot on the right side-usually hidden inside the wing cavity- there is a 2 plug harness, this was used with the original system scanning tool. If this connecter gets wet etc it can cause a whole range of problems. Check it is dry and not sitting in the bottom of the cavity!

Submitted by kevin@evepartn… on Fri, 03/16/2012 - 13:23

I suppose I could connect a battery to the positive side of the coil and connect the negative side of the battery to the spark plug thread to see if the spark improves (this would circumvent the ignition switch) If that is to no avail, I could connect a second separate battery in the same fashion, this would circumvent the ign. switch and the starter relay. By the way, I have also tried disconnecting the lead to the alternator, in the event it was draining voltage (no difference) I will say that when the car is running perfectly at idle the voltage at the battery is 13.5 volts.

Submitted by dougdwyer1@com… on Fri, 03/16/2012 - 13:20

How often does the problem occur? Once a month? Once an hour? If practical I'd try running a dedicated power supply wire to the coil and see if anything changes.

And/or embark on a mission to thoroughly check/clean/tighten all relevant wiring and connectors. If you have a schematic it'll help in tracing the ignition circuit.

Oh....remove the under-dash panel and gently jiggle the wires and the back of the ignition switch. If the engine falters, you've just hit pay dirt.

(I might add that, with these older Jags, a Saturday spent cleaning and tightening every connection and ground point you can put your hands on will often go a long way in ensuring happy motoring. Don't forget the fuse clips and fuse end caps....both of which often corrode)

Cheers
DD

Submitted by kevin@evepartn… on Fri, 03/16/2012 - 12:55

You are correct, it is a 1986 XJS with lucas ign. I have noticed that the interior lights dim consistently with the varying RPMs. Also placed a lead on the primary coil and it dips below 12 volts.

Submitted by dougdwyer1@com… on Fri, 03/16/2012 - 11:28

Kevin, have you checked voltage to the primary coil (when the problem occurs, obviously)?
I'm assuming this is an 80s vintage XJS with Lucas ignition, yes?

Cheers
DD