How can I find out they year of my jag V12 I think it's a XJS Engine numbers 8S4240LB

Not sure about the horse power, but the Jag V12 has a capacity of 5.3 litres

https://parts.jaguarpalmbeach.com/p/Jaguar__XJS/Fuel-gauge-sending-unit-fuel-sender-unit-fuel-tank-sending-unit/49193626/DAC11188.html?partner=googlebase_adwords&kwd=&origin=pla

The sending unit is in the gas tank...(its #9) ..good luck

Year/make /model?? Most all oil pressure sensors just screw into the engine block. Some require a special socket for removal but most can be removed with pliars

Jaguar Sensor, XJ6, XJ8, XJS, XK8, S-TYPE, X-TYPE, XJ40 ...

www.jagbits.com/jaguarsensor.php
FITS: 1993-1994 6.0 XJ12 AND 1989-1993 V12 XJS FROM VIN 157118 ON, 1994-1996 6.0 V12 XJS FRONT DAMPER .... LNA1622AA - MAP SENSOR ... C42166-USED - USED SENSOR COOLANT TEMPERATURE FOR FUEL INJECTION

Thread: 6.0 V12 XJS High RPM When Warm - Jaguar Forum.co.uk

www.jaguarforum.com/showthread.php?t=54266
Mar 3, 2013 - I recently bought a 1993 6.0 V12 XJS and when it is started from cold it runs ... to 1300 RPM so it wants to surge forward when braking which is strange. ...Classics · XJS 3.6,4.0,5.3 & 6.0; 6.0 V12 XJS High RPM When Warm ... You might want to adjust the aux (extra) air valve to bring the idle speed down.

I would start with a tune up, then isolate any symptoms other than lack of power if it persists, like rough idle, sputtering, jerking, engine trouble codes, etc.

I would get complete set of maintenance records for that one. 250k is alot for a jag especially a V12. That one is either running on borrowed time or has been meticulously taken care of.

Sat dry for 2 years - Oil or Money??

Get your biggest barge pole and don't go near that car without it!

Unless you have the time, experience and money to expend to get it going again?

At that age the Jag's weren't built like they are now (metal alloys, etc..) I would suspect that if you tried to run it, you would need a new gearbox within 2000 miles.

have you tried reversing the pipes and see if that makes any difference other than that there must be a pressure difference between the two pumps try priming the filter with oil before starting.

Chances are the coolant temperature sensor or its wiring have failed, or the vacuum line to the MAP sensor is leaky or broken (I believe the V12 in '89 guise uses MAP sensors). The MAP sensor measures Manifold Absolute Pressure. Along with this pressure the ECU looks at engine RPM. It also measures air temperature. Knowing pressure and temperature we know density, and knowing engine speed tells us how much volume of air is going through the engine. All of this together is computed into air mass and is used to calculate how much fuel mass should be admitted. If the vacuum line is broken, the ECU reads less vacuum and produces rich mixture thinking that the engine is under high load.