can you use an 1987 xjs v12 as a replaclement engine in a 1990 xjs v12?
I have done some checking and i see a differant between the 89 and 90 engines but not sure what. can't i just replace all the fi system and be good to go is how much more would i have to do thanks ray

 

The engines are fundmentally the same but I fear the details might be a problem.

My one immediate thought is the the 1987 engine has no mounting facility for the two crankshaft sensors which are required to operate the 1990 fuel injection and ignition systems. Swapping the timing cover might solve the issue for the front sensor but I'm not sure about the rear sensor.

There might be other detail differences.

Hopefully others will chime in.

Cheers
DD

 

thank you this info will save a lot of time ray

 

Yes....

Other differences
Marelli ignition
-different distributor
- Possibly different C/R my 1989 12.5:1
- 1 crank VR sensor on the front
- 1 sensor on the fly wheel for engine speed
- Combustion chamber volume increased (6L only)

The axillary air valve might also be different as some of these functions are PCM controlled. The book is a bit vague on when this change was made.

The rear main seal was changed from rope to lip I believe around 1987/88. Rope seal crank and block can be machines for lip seal.

Doug is right the engines are fundamentally the same and you can use an older engine and bolt all of the ancillaries from a newer.

cheers WJ

 

As others have stated, the motors themselves should be the same but, the ignition and other systems are much different. the xjs underwent quite a few changes in 89-90

for ex...
Warrjon's car is an 89 and marelli ignition... my car is also an 89 but, has the older Lucas ignition system...