Good Morning all,
My name is David Moran and I am British, but live in Spain. Over the years I have had a number of Jaguars including a Series 3 E- Type, XJS 3.6 Coupe, currently I have a 2005 XK8 Convertible, a 1987 XJS 3.6 Coupe and my wife has an E Pace. I have been a member of the forum for some time but have not posted before. Technically I have done a lot of work on the cars over the years but am not an expert, particularly when it comes to electrics and electronics.
I now have a problem with the XJS that I cannot figure out and would appreciate some advice if possible. The car was running normally up to about 6 months ago. It passed its annual Spanish road test including the emission tests. We then had a problem when an incorrect relay was fitted to the ignition system resulting in damage to the wiring and a no start situation. This was repaired and the car ran normally for a couple of weeks. It then started to run VERY RICH with lots of smoke. The fuel pump, filter and pressure relief valve are all new. The fuel pressure at the rail is correct. We have checked for vacuum leaks. The ECU was fully rebuilt by AJ6 Engineering in 2018 and has done little mileage since then. There appears to be an intermittent problem on the ignition side which could be part of the problem. This car has Lucas 45DM6 Distributor with electronic pick up., a new compatible coil and an Ignition amplifier. There is no CPS, but a pick up from the amp to the ECU. I am having great difficulty finding replacement parts and would like to fit a more modern electronic ignition if that is possible but do not know how to deal with the pickup for the ECU.. I have a new Pertronix LU167 pickup which I think is compatible and a 3 Ohms Pertronix Coil. Can anyone advise me if this option will work with a modified feed to the ECU. If not does anyone have a workable solution. I just want to get my baby back on the road for the summer !!! Many thanks in advance. Regards David Moran

 

Hi David, I know you were advised to post in the XJ40 section but in your case the ignition system and Lucas 8 cu ECU are particular to the XJS 3.6 models up to1987, in fact the ignition set up is very similar to the Series 3 4.2 which also uses the 45DM6 distributor. The Ecu and the ignition are two separate systems that run independently from one another( unlike the xj40) apart from the ‘pick up ‘ you refer to which simply gives an engine speed signal to the Ecu either via the coil neg terminal or a resistor in the Amplifier. The position of the crankshaft in this case has no bearing on injector firing, again unlike the XJ40.
So, in my opinion, you have two separate faults , firstly the rich running , a common early 3.6 xjs issue if you look on the AJ 6 engineering Jagweb site this goes into great detail, but worth also checking the resistance values of the coolant temp sensor and checking the state of the plugs to see if an injector has stuck open.
Secondly the ignition, personally I would stick with the original set up of which there are really only 3 working parts, the pick up module, the coil and the amp.If no spark is to be had then check for battery voltage at the neg terminal of the coil, if this reads zero disconnect the lead that goes from the amp to the coil negative, a zero reading again would indicate a faulty coil, a battery (12v) reading would suggest faulty amplifier. The pick up module can be tested by checking resistance between the two terminals that go to the amp, should be between 2.2 and 4.8 K ohms. Obviously 36 + year old wiring can also give issues and rotor arms , distributor caps and leads dont last forever! If you did go down the route of an aftermarket market ignition system I would imagine that the ecu could be fed from the coil neg terminal possibly with a resistor but I have no experience with anything other than the standard spec
Regarding spare parts I would have thought these were still readily available from the like of Manners, Robey and Barretts etc.
Good luck and hope you get it sorted so you can enjoy those great Spanish roads!
Regards Simon

 

Hello David:
I too have a early XJS that originally came with the 3.6L AJ6 engine and the factory manual transmission. When I got the car it just would not start and when it did, it ran like crap.
My eventual solution was since it had the same 3.6L engine was to convert the car to the complete engine management system from a 1988 - 1989 XJ40.
At the time when I did there were several of these early XJ40 cars in wrecking yards near me so I was able to scavenge the appropriate parts from those cars fairly easily.
The engine management system off the XJ40 with the hot wire mass air meter, pulse width modulated idle air control valve and ECU controlled ignition timing is WAY superior to the early EFI stuff that was originally on the 3.6L XJS cars.
Except for some extra wiring (6 - 8 wires as I recall) that had to be run from the engine compartment back to the rear of the car where the ECU is located, all of the necessary parts just bolted on.
This ended up being a huge improvement to the car. I have since also converted the car to a 4.0L AJ16 engine but I am still using that engine managent system from the 1988 - 9189 3.6L AJ40 cars.