Those who criticise the original XJ40 of 1986 should bear two things in mind. Firstly, without the XJ40 there would never have been an X300, a car now acknowledged as one of the company’s best efforts. Even the subsequent XJ8 owed a significant proportion of its body and chassis to the Forty. Secondly there’s the small matter of cost, as the entire model programme cost Jaguar less than Mercedes, over the same period, spent on the rear suspension alone for their new small car the 190E.

Few sheets of paper come cleaner than the one that the XJ40 was laid out on, excluding the 3.6 XJ-S used to trial the new AJ6 engine, the only link with the past were the bore spacing and the use of a single V12 cylinder head on the 2.9 litre variant. With hindsight it’s easy to say that the introduction of so much that was new, and untested, made the reliability issues that arose inevitable. However, there was little wrong with the underlying engineering, it was quality control at several external suppliers that caused most of the trouble.

Designed around a brand new all alloy 24-valve engine (mated to Getrag five speed manual or ZF four speed automatic gearboxes), the XJ40 was as new and advanced as its predecessor was traditional and to be honest, out-dated. With no less than seven on board computers its specification included ABS, Citroen like hydraulically boosted brakes, climate control that increased cooling when the car was in direct sunlight, a digital dashboard and a revolutionary new electrical system that cut wiring bulk substantially by running only one power cable to each corner of the car and then operating all of the lights at that corner via remote modules and small signal wires.

The new cars underpinnings were no less advanced with a rear suspension layout that mounted the differential in a pendulum arrangement and allowed the wheels to ride back slightly when they hit a ridge or pothole in the road. An added feature on the more expensive Sovereign and Daimler variants was self-levelling suspension, run from the same engine mounted hydraulic pump that powered the brakes.

As with the previous XJ there were XJ6, Sovereign and Daimler variants, the XJ6 available in both 2.9 single cam and 3.6 twin cam form, the Sovereign and Daimler available only with the larger engine. One element missing from the new lineup however was the XJ12; legend has it that Jaguar engineers deliberately made the engine bay too narrow for a vee-format engine so that the company’s former British Leyland masters could not force the fitting of the Rover V8 as a cost saving measure; however it’s just as likely that the effect of the fuel crisis on sales of the original XJ12, together with a general move away from large capacity engines, not to mention the cost of manufacturing such a complicated power plant also influenced the development for the new car until it was too late to incorporate the V12; ironically by 1986 V12 sales had picked up significantly and the Series 3 XJ12 and Daimler Double Six were forced to soldier on until 1992 when the V12 XJ40 finally arrived.

Work on various improvements must have already been underway as the first XJ40s rolled off the production line as within three years an updated car was announced that rectified many of the early criticisms. Virtually unchanged from the outside, with the exception of new chrome trim around the tail lights on Sovereign and Daimler cars, the big news was an increase in capacity from 3.6 to 4.0 litres; the power output remained virtually unchanged but peak torque was up considerably and arrived a lot sooner, recapturing, to a degree the effortless feel of the old 4.2 XK engine. The automatic gearbox  was upgraded on 4.0 litre cars to include electronic control with sport and normal settings plus the ability to retard the ignition slightly for smoother changes. For the time being the 2.9 engine continued on unchanged until a new 3.2 twin cam arrived in 1992 to replace it.

Underneath there were also big changes with an entirely new Teves braking system that used an electric pump to store the brake fluid under pressure and was mated to ATE rather than Girling calipers, the engine driven pump by now only fitted to the few cars that optioned the self levelling rear suspension.

Inside, traditionalists must have been glad to see the digital dashboard replaced by conventional analogue instruments, and an indicator stalk that stayed where it was put when used, rather than returning, rather confusingly to the centre position. New, stronger external door handles now incorporated Chubb locks for added security.

Though externally similar to earlier XJ40s, other than new side repeater lenses and fog lights integrated into the lower valance, the 1993 model year cars featured an entirely new substructure forward of the windscreen in order to accommodate the extra width of the revised 6.0 litre V12 engine, mated at long last to a four speed automatic transmission, something the old 5.3 had been crying out for.

Inside, all cars received new, more shapely seats with adjustable headrests along with new door trims, an updated climate control switch panel and the option of different colour dash casings to coordinate with the rest of the interior trim. There were also two new models, the 3.2S and 4.0S, which pitched the XJ at a new younger market, sporting as they did five spoke alloy wheels, slightly stiffer suspension and more supportive seating.

A joint venture between Jaguar and TWR, JaguarSport offered styling, interior, wheel and suspension upgrades over and above what could be chosen from the standard options list, along with an integrated package known as the XJR, which in 3.6 litre form retained the standard power output but with the 4.0 litre engine featured a new inlet manifold and revised fuel mapping for a modest improvement in performance.