Good evening gents, yesterday (thursday) I drove 13-14 hours from Virginia to outside of Boston MA. Came up for a memorial service for an uncle that passed. Had a failed fuel system relay that had prevented it from starting but replaced it and all seemed good. Had no problems cruising at 70 mph most of the way and went to start it this morning for a quick errand (being Friday) and got to the destination a couple of miles down the road parked and would no longer start. Had to have it towed back to lodging.

Checked many different circuits. Jumped the fuel pump sockets and the pumps run. Jumped the fuel system power relay socket and the fuel pump runs. Fuses are all good. Power to and from the inertia switch is present but not the full 12v. Same low voltage shows up at the fuel injection power relay. Power coming from the ignition switch WK and W show full B+. Power at the fuse to the injection relay is low. Power on both sides of the socket that connects to the ignition switch is B+, no loss, or minimal there.

Hot wired the injection circuit to run the pumps and still no start. Cranks over fine but won't fire up. Cannot figure out why voltage to injection circuit for turning on the relays is low as this does not turn the injection system on. Tomorrow (actually today at this point) I will verify spark. Did replace the forward crank sensor but have the old one in the trunk (I think).
Supposed to head back to VA on Monday but not looking good right now. Might have to leave the car.
It's a '94 6.0L convertible.

Anyone know somebody near Boston that might be good with this, or any good suggestions or ideas on what to do next?

 

Turns out that it seems like no spark as well. Well, won't be able to do anything more with it until tomorrow.

 

Problem is solved at least temporarily. Seems there is some kind of voltage drop between the ignition switch and the right hand fuse block. It seems that the fuse for the fuel injection main relay-ignition power was not getting full power from the ignition switch. Somewhere past the multi port plug beneath the steering column there is a poor connection. The multi port plug carries 2 switched power supply lines and the one that actuates the starter circuit. This plug also had a brown wire that had been cut off on both sides of the plug. I have no clue what it was for nor was there any trace of the wire in sight. However when the 4 port plug was separated there was evidence of overheated connections due burn residue around the white wire connections as well as the brown wire that was cut off on both sides of the assembly. Definitely evidence of overcurrent damage or poor spade connections within the plug itself.
To facilitate restoration of full power to the ignition circuits a jumper was attached to the white wire coming from the ignition switch across to the right side fuse panel where keyed power needed to be and a fuse applied in the normal manner as circuit protection. This seems to have resolved the issue, at least for now. I'll be able to drive home.

 

On the first page of the XJS forum someone posted a checklist of items to look at to help diagnose a no start.
I do feel your pain. I would really hate driving hundreds of miles from home and then end up in a no start situation with my XJS.

 

Yeah, that's mainly pre-marelli era. Good thing I had my laptop with all the electrical diagrams as well as a few print outs I made. Just looked at the basics first and verified what I had and what I didn't. No EFI will run without full voltage so that was the problem. Seems that there is a bad connection between the ignition switch and the fuse for the engine management systems. Ran a jumper over to the supply side of the fuse so that I could leave a fused connection to the load side of the fuse block. That way I could also make sure that any other systems running off of that circuit would have full power as well. Also seems to have been an overcurrent load through the ignition circuit evidenced by the slightly toasted spade terminals inside the connector from the ignition switch under the steering column. Also a big question is what the brown wire was hooked to that was cut off on both sides of the connector. I'll have to worry about that later. Right now it runs fine and got me back home.
Just another thing to put on the list to sort out later. Just haven't had time to search the electrical diagrams for what the brown wire does. See your from Boston, what part?

 

At least your got back home!
I'm in Wakefield, MA.

 

I had a 94 6.0 with a fuel problem that went UN-diagnosed for about six months.
The only way I could use the car was hot wire the fuel pumps to 12V.
I forgot to unhook the wires several times which left me with a dead battery.
What. it turned out to be was a bad fuse for the heated O2 sensor.
That fuse is in the trunk and I never checked it until a long time Jaguar mechanic took the wiring diagrams home with him one night,
He found the answer and was 100% right.

 

Ive been having similar crank no start issues with my 95 xjs4.0 this is the second time ive heard about something faulty with the ignition switch. So im quite curious how you wired it? I believek a 95 wiring and fuses are different from your 94 but i have all the wiring diagrams. Id love some advice on this

 

Ward,
If the problem is lack of fuel pump action, find the Heated O2 sensor fuse.
On the 94 it is located in the trunk.
If you just need to get it running, unplug the FP harness from the relays.
Take these wires and hot wire them to the battery.
ALWAYS UNPLUG THESE WIRES WHEN YOU GET TO YOUR DESTINATION.
Ask me how I know.

 

Im getting fuel did a pressure test plus i can hear the pump priming. Just check the following with ignition swichted to position two i seem to have 12 volts across the board at the right fuse panel. I did not check this while cranking the engine and wonder if i should. Im attaching a picture of my 95 fuse diagram for reference.ifigure 7 would be the correct fuse but checked them all

 

I have both wiring diagrams and under the steering column is a large black 4 way connector. It has three large gauge wires and one smaller. The heavy white wire is what feeds the circuit for the fuel and spark ecm's. It list's fuse 7, which is located on the passenger side interior fuse block. It is a 15a fuse listed as engine management power. This feeds both fuel and spark. Mine had low supply voltage. 7volts which isn't enough to run any control module. Even though I hated to do it, I splice into the large white wire with a 14ga wire and fished it over the top of the radio behind the dash so it wouldn't be seen and tapped into the supply side of the block with a "Y" to bring power over and still facilitate using a fuse for circuit protection. Now it's held in a fuse holder instead of the block but got me going.
Attached you'll find the '95 wiring diagram.

 

So with my key in position two im reading 12 volts at the #7 fuse. My question is should i be cranking over the engine ,essentially key in start position,and check for 12 volts at fuse #7 then?
thanks
Jeff

 

That correct, should be the same in run and crank. But you seem to have what you need as far as power goes. I'd check what Grant Francis mentioned in his reply to you in the other thread as well.

 

Will do