Possible causes of no spark at coil 1991 XJ6
 

what are the possible causes of no spark out of the coil

Er , broken coil? but I think you will get a better response if you post this question in the correct section

Welcome to the forum elsan13,

I've moved your question from XK8/XKR to XJ40 forum. Members here with the same model will be able to help.

Please follow this link New Member Area - Intro a MUST - Jaguar Forums - Jaguar Enthusiasts Forum to the New Member Area - Intro a MUST forum and post some information about yourself and your vehicle for all members to see. In return you'll get a proper welcome and some useful advice about posting to the forum.

Graham

Hi elsan13,

Welcome to the Jaguar Forums! It's great to have you with us.

The most common cause of no spark at the output of the coil is low battery voltage while cranking the engine. If the cranking voltage falls much below 11 volts, the Engine Control Module (ECM) will not trigger the ignition to fire.

Another possible cause is failure of the Crankshaft Position Sensor (CPS). One clue that the CPS may have failed is if the tachometer reads 0 rpm while cranking the engine - it should read about 200 rpm if the CPS is providing a plausible signal to the ECM. Failure of the ignition amplifier (mounted below the coil on a flat metal heat sink) could cause similar tachometer behavior, but ignition amp failure is far less common than CPS failure.

Other possible causes include failure of the ignition coil, deterioration of the wiring at the coil or amplifier, or other problems in the wiring, especially corrosion or looseness on battery power connections and grounds.

The Electrical Guide shows the wiring for the coil and amplifier. You can download it here:

Jaguar XJ40 Electrical Guide 1991

You can download the Engine Management System manual here:

Jaguar AJ6 4.0L Engine Management System / OBDI Diagnostic Guide

Cheers,

Don