XJ40 Problem when hot (idle and power)

Hello everyone, I’m from the south of France and new to the forum. Since May 2019 I am in the process of refurbishing a Daimler XJ40 4.0L but I encounter electronic problems around the engine.

In my case, the car has hot misfires and little or no power for a 220 horsepower car. I suspect the passenger side ECU or microprocessor.

I changed the entire ignition circuit, inspected the fuel circuit and tested the engine compressions and everything is fine, I am a little lost.

I took these videos to better understand the problem:

If someone has an idea to offer me I am interested


Is the exhaust free? Could it be lean (you checked the fuel circuit, but maybe analyze the exhaust)? How is the engine at higher rpm?
Best of luck!

Thank you David
It’s just missing the rear silencers. The engine at high revs has no problems, just it seems to me that it lacks power. To test I will soon bring back a 3.6 xj40 without catalyst and I will see the result.


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Have you ever replaced the fuel pump? If not check it out, they have a problem with “fluttering” but it normally occurs in very hot weather ie. over 80 f

Looks like it’s a 1990 MY car. All the gauges are analogue. Do they have an intank fuel pump in a plastic canister? If yes then the blue donut seal at the pump’s outlet might have failed allowing some fuel to flow back creating a low fuel pressure. Do a fuel pressure check.

The petrol pump I never looked at it but I installed an adjustable pressure regulator on the injection rail with a pressure gauge which confirms to me that the pressure is good even under acceleration and under heavy load.

It is a car from November 1989 it has everything of a car from 1990 I think. For the fuel pump it is located on the rear axle and not in the tank but I plan to dismantle it to clean it and see what is hidden inside soon.

Have you checked the fuel filter yet?

Yeah fuel filter is new, just 2000km