XJS 1983 body, 1986 Engine

Hi guys,

I’m here to ask you for your help.

I have a 1983 XJS 5.3 V12 H.E. It was left in a gardenhouse for 15 years and now i’m the proud owner.
Mouses had lived in my car and made heir toilet on my engine.
That’s why i bought a new engine and installed it. a 1986 engine.

Now my car wouldn’t start anymore. I tried the original ECU (1983) but it is broken. And i tried the new ECU (1986) but that did’nt work out.

I called a mechanic and he said: ‘’ the car is from 1983 and it is not corresponding to the 1986 engine.’’ is it true?
Or what do i have to change to let him run?

Main questions:

  1. is it possible to put a 1986 engine in a 1983 XJS?
  2. Must i change sensors or other parts to let it run?
  3. should i buy the 1983 ECU or keep on going with the 1986 ECU?

In hope to hear from you, guys.

Much love from the Netherlands.

Arnold

Part numbers from the ECUs would help but I doubt that you have a compatibility issue; there’s a large degree of interchangeability with V12 HE ECUs. A defective ECU is certainly possible, though.

There are many possible reasons that your engine won’t start.

Just to get the conversation started…

Go to the basics: do you have spark and fuel pressure? Are the fuel injectors operating?

A faulty “coax wire” is very common; that might be a good place to look if your injectors are not firing. Tons of archived discussion on this, including a recent thread.

Cheers
DD

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I agree, I just swapped in an 85 motor into my 83 and most parts are the same. It is probably an issue with one of the basics. Fuel, spark, wiring etc. I just spent the last month running down everything on my car and finally today it seems to be running normal. Tracking things down can be maddening, you just can’t give up. Regards

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hi! thanks for helping:)
I think i have a compatibillity issue too, but how can i solve?

i have the option to buy a ECU from 1983. Should i do it?

My car has fuelpressure & spark. Thats not the point. It should be an ECU problem.