I am looking to replace the 3.6 engine in an '89 VDP LHD with a 4.0 from a very basic XJ6 RHD built later that same year
Since I never liked the digital IP and knowing that it is prone to failure would also swap the IPs.
The idea was to take everything engine and electrical related from the 4.0 XJ6 and put it in the 3.6 Daimler, that means engine, gearbox, ECU,
I understand this was a quite usual conversion even only dropping the 4.0 in place of the 3.6, I imagine zding the whole line of components should be much easier but I haven't found a thorough walk-through yet.
Could someone please confirm this first hand or point me to the right place to look at?
Thank you

 

Hi aquilla,

Welcome to the Jaguar Forums! It's great to have you with us.

Over a 20+ year period, I owned an '88 XJ40 and a '93 XJ40 and have been very active on the Jaguar forums since the mid-'90s, and I don't recall the 4.0L for 3.6L conversion every being "quite usual," at least not in North America, the U.K. or Australia. In fact, I can't remember anyone who has actually done it, or where you might look for photos of the procedure.

One significant issue I can think of is that the 3.6L cars had the hydro-mechanical ZF 4HP22 transmissions, while the 4.0L cars got the electronically-controlled ZF 4HP24 transmissions, which means you would need all the wiring for the Transmission Control Module (TCM), and you would have to use the Engine Control Module (ECM) from the 4.0L since the ECM and TCM communicate together to orchestrate smooth gearshifts. You would also need to swap the J-gate gear selector assembly because the electronic transmissions require the decoder module, and also you would need the transmission relay and its associated wiring. So to use the 4HP24 transmission you would need to swap the engine management and transmission control harnesses at the very least. However, it's quite possible that the 4.0L engine would bolt right up to the 4HP22 transmission, but I don't know if it would run properly on the 3.6L ECM.

Another potential issue I can think of that could cause problems using the 4.0L engine and transmission is that the differential in the 3.6L cars was usually the 2.88:1 unit, but in the 4.0L cars the ratio was different. Our '93 had the 3.58:1 diff. This could cause issues with the electronically-controlled shift points coming at suboptimal road speeds.

If I remember correctly, the fuel injectors are different between the 3.6L and 4.0L cars, and have a different impedance and require a different drive signal from the ECM.

I do not know if the later analog instrument clusters are direct replacements for the vacuum-fluorescent clusters or if there are differences in the electrical connectors and/or wiring.

You can probably answer many of these questions by studying the documents at the links below.

Jaguar XJ40 Electrical Guide 3.6L 1988-1989

Jaguar XJ40 Electrical Guide 4.0L 1989-1990

Jaguar AJ6 4.0L Engine Management System / OBD1 Diagnostic Guide

And you can compare part numbers at this link:

Jaguar Land Rover Classic Parts

Cheers,

Don

 

Don, thank you for the explanations and links. The project car, 1989 Vanden Plas Majestic 3.6 is complete and even if left unused for many years in a good technical condition. I was going to strip everything from it for a thorough clean up and paint job and in the process to use the 4.0 later 1989 with analogue IP as a donor to upgrade the engine and all the mentioned parts. I would very much use everything that makes the swap from 4.0 to the 3.6 an easier and consistent upgrade and not merely a hybrid of some sorts. This came to me after I read that only a few of the Majestics were powered by the 3.6 and the majority by 4.0. It would be interesting to find out the exact spread of them.

Can the cable loom be transplanted easily from one car to another?
The more I ask, the more I think I will stay with the more sane and logical decision of restoring it to its 100% original condition. It certainly retains more value this way.
I was hoping to find someone here who did that and either encourage me or bring me back to my senses with my endeavor.

 

Welcome to the forums aquilla,

It's more than twenty years since I last owned an XJ40 but I still follow the forum posts. My impression is the same as Don's - conversion from 3.6 to 4.0 is far from being "quite usual".

Graham

 

I have actually done this exact thing on a 1985 XJS that was originally built with the 3.6L AJ6 engine and the factory 5-speed manual transmission.
I purchased the car around 2007 and it was a non-runner because the original Lucas Digital-P fuel injection system was not functioning well enough to start the car let alone run it down the road.
I initially ripped out the Lucas Digital-P fuel injection system out and replaced it with the complete engine management system from a 3.6L 1988-1989 XJ40 car.
Then a couple years later the compression in the cylinders of the 3.6L got so bad that the car would not start.
I think all the overfueling from the broken Digital-P system washed the cylinders down with extra fuel for so long that the engine had MULTIPLE broken rings on the pistons.
This was confirmed later when a friend tore the old 3.6L apart and found many many broken rings.
At that point I acquired a 4.0L AJ16 engine so I pulled the worn out 3.6L AJ6 out of the car and replaced it with the 4.0L AJ16 long block.
I kept all of the original 3.6L intake manifold and all of the XJ40 3.6L engine management system.
I temporarily installed an aftermarket wide band O2 system in the car to monitor the air/fuel ratio to see of the 3.6L XJ40 ECU and mass air meter seemed to be handling the the increase to the 4.0L AJ16 engine without causing a lean condition.
As far as I could tell the system worked just fine and I still have the car running in this configuration to this day.

 

Hi fellow Jensen owner (I own a 68 Interceptor ),
Really interesting reading about your experiences. I am the new owner of a 1986 XJS 3.6 with 5 speed. It runs, but with hesitations and hiccups. First morning start it runs beautifully, so it seems the mixture when warmer is not correct. That would point to the well known Lucas 8CU ECU problems (A COMMON PROBLEM WITH THE EARLY 3.6 XJS (1983-87) / AJ6 Engineering).
So... I am thinking about the possibilities to solve this. It seems to me it should be pretty easy to replace the current air intake system & ECU with one from a 3.6 XJ40 and if I read correctly, this is what you did.
Can you elaborate a bit? What exactly is needed from the XJ40? Is there space enough? Did you need to change the wiring - does the XJ40 also have the ECU loaded in the boot? Did you have difficulty in adding sensors (crankshaft sensor I would guess)?

 

I used the original XJS 3.6L intake. The XJ40 ECU is under the passenger's side of the dash. I used as much of the wiring from the XJS engine management system as I could and spliced a 6inch pigtail from the XJ40 to the XJS engine management wiring termination in the trunk of the XJS. I ended up running an additional two or three or four wires from components in the engine compartment to the XJ40 ECU harness pigtail in the trunk since not enough wires are present in the original XJS engine management harness. The boss and threaded holes used to bolt up the crankshaft sensor bracket are there on the XJS 3.6L engine but the dowels that actually locate the bracket have to be inserted into the existing holes that are already there on the timing chain cover.

I did this conversion over ten years ago so I may miss something but off the top of my head from memory the parts you need from a 3.6L XJ40 are:

engine management ECU with harness plug and 6 - 8 inches of the XJ40 wiring harness to splice to
distributor
mass air meter (also with wiring plug and 4 - 5 inches of wiring to splice to)
crank sensor with wiring plug, wiring pigtail, bracket and dowels
crankshaft damper pulley with toothed wheel
idle air control with pigtail
XJ40 fuel injectors
XJ40 throttle body

When I did this conversion I also swapped out the HEAVY GM A6 AC compressor that came originally on the XJS 3.6L for the lighter aluminum AC compressor from the XJ40 car and swapped out the high amperage alternator as well.
Both of these required the XJ40 mounting brackets as well. After this conversion with the AC compressor, crank damper, and alternator the XJ40 accessory drive belt is also used.

There might be other things I am forgetting sunce I originally did this conversion back around 2007 from what I recall.