Hi Shanon,
Before we tackle the no start condition I wanted to address your statement about knowing your 1995 XJS " isn't spectacular by Jag lover standards ". The fact of the matter is the XJS was produced for 21 years and we can thank a delay in getting the XK8 ready and Fords money for the 1995 and 1996 XJS. I would argue that the 1995 and 1996 XJS is the most spectacular of the lot due to all the refinements and updates including the AJ16 4.0L engine. Each year of the XJS has it's quirks and issues but I can assure you the 1995 XJS is a spectacular Jaguar and I am proud to show mine off at any show or gathering.

Now back to your no start issue. I suspect that your no start issue may be related to the alarm system from your description. I had purchased a 1995 for a parts car and when I was pressure washing off the engine ( I had it running while I washed it off ) the engine died and would not restart. I put on a spare crank sensor that I had to see if that was the issue and it did not correct the no start. From all the research I did on this issue it appears that the alarm system on the 1995 XJS is set up such that if it picks up a disturbance like excessive water on the engine which tells one of the sensors to shut the engine off, the alarm system can send a message to to the ECM basically telling the ECM to not allow the engine to restart which I assume is to protect the car from theft. I found this out when doing my research when another AJ16 owner was washing off their engine and it shut off. The only thing that fixed the no start issue was switching out the ECM which allowed the system to reset and the car started right up.

I wonder if the wire you found under the dash that had separated might have done the same thing by telling the ECM that your car was trying to be stolen and therefore the ECM shut the system down. There must be a way to reset the ECM and tell it that it is ok to allow the car to start without having to put a known good ECM in your car to reset the system but I am not aware how to do this my self. I know that on the one I read about that the owner swapped a good ECM from a friends running XJS and after the swap and reset the owner put back in the original ECM and the car started fine so again appears to be a reset issue.

I hope this info helps you to have some idea what may be going on with your no start issue. I purchased a disc that had all the dealer service books on it for the 1995. I purchased the disc on E-bay years ago and it was like this one :


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1992 to 1996 Jaguar XJS (All Engines) Parts and Service Manual on CD-ROM (Used)

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Could it be that all you needed to do was to disconnect the battery for a period of time and reconnect? Putting in the other ECU merely made you disconnect the battery and reconnect. maybe?

 

Hi Shannon

Speaking as the owner of an XJS of the same year as yours that doesn't start, I'm hardly in a position to offer you any advice and so instead I will make some suggestions that 'may' or 'may not' help, based on everything I've tried so far

Start with a fully charged battery (as already suggested) but when you Crank her over, if the Tacho shows 1,000 rpm then it is very unlikely to be the CPS (although it 'could be')

Then check the Fuel Pump Cut-out in the little plastic box on the passenger door pillar, where if it needs re-setting you just push down the plunger in the little hole, either with your finger or the end of a pencil

Next check every fuse on the Car, especially the ones that are underneath the passengers knee pad, where you have to pull down a flap in order to get to them

Where I was amazed to find, although I'm not sure why, a Fuse for the ECU! and though that fuse was fine on mine, on yours it night not be

If none of that gets her Started, then you could always follow everything I did to try and find the cause of my 'No Start' problem but since you got water in the Car, it may have got through to the ECU, which may need taking off and drying out

To save me writing it all out again, you can see what I did to find the Fault on my 'Cherry Blossom' restoration thread, where it seems that the problem was down to blocked Injectors and when I fit the New ones, we will see!

There are loads of Photos on there of everything I did, including where to find the ECU and take it out

Fault Finding My 'No Start' Problem on my 1995 XJS with AJ16 4.0L Six Cylinder Engine

 

A good healthy battery (if you haven't got one already) will make the world off difference. If you have a multi-meter you should measure the voltage at the battery with the car off. Anything below 12.2v is not a good thing. You can also do volt drop check while attempting to crank the engine (not really applicable in your situation). The voltage should drop 2-3 and REMAIN at the lower voltage. If the voltage gradually lowers throughout cranking, it's probably done for.

 

How is the water getting from the door into the carpet?
If there is standing water in the door it means the drain holes are blocked; even so I would have thought that any water getting out would have run down the inside of the door and underneath?
Wet carpets usually mean roof drain tubes blocked or wiper scuttle tubes blocked which can somehow back up iwo of the heater box and run out from under the dashboard.
I think.