XK8 won't start after sitting
 

I just replaced the timing chains on my 98, after it sat parked for about a year. It's had a battery maintainer installed, but I tried a new battery anyways. Also with my Li-ion jump box attached.

The lights dim and HVAC turns off when in key position III, as if it's going to start, but there's no starter relay activation.

I didn't have ground from the N/S switch to the body processor, so I made a jumper to spoof ground to terminal 7(RU). That made no difference.

EMS relay is activating in key position II.

I can ground the starter relay on the control side and they engine cranks flawlessly, but will not start.

The GO wire from the body processor to the relay control circuit never shows ground, and grounding it at the module does not activate the starter relay.

All fuses have been checked and I have power and ground at the body processor module.

The large shift position sensor on the passenger side of the transmission does not seem to connect to the starting circuit, from what I can tell. The RU wire to the body processor comes from a different N/S switch.

I haven't been able to pull codes on it yet.
https://cimg5.ibsrv.net/gimg/www.jag...8d8020a638.png

EDIT Is the Neutral switch Open or Closed in N ?

If you can ground the start relay at pin 2 and it cranks but not if you ground at the BPM 73 then you have a break in that wire. As it does not start when grounded at the relay then I would suggest that the ECU is not getting the ground signal so the break is between the ECU splice and the relay - probably at one or the other.

However that is different problem to not getting a ground signal coming out of the BPM so a bit confused...

I am assuming from your description that you are getting power on Pin 1 of the relay to indicate that the immobiliser is happy ?

I have power on pin 1. Just missing the ground signal on the GO wire.

HI, I have exactly the same problem which I listed on the forum a few days ago. I have done all the same tests as you, I put a ground on the EMS relay and get the same readout on the starter relay. The car had been running fine, left for 2-3 weeks and no start! One question to see if we re chasing the same fault. When the ignition is in position 2 if you press the brake pedal does the shift inhibitor solenoid operate, ie do you hear a click and you can then move the shift lever?
I fitted a known working ignition switch from my XJ8 just to prove to myself that it's not a switch fault but no difference. A strange thing is that the EMS relay doesn't operate if the starter relay is removed yet the starter relay doesn't operate so no circuit is made....so how can that be!!!???
Finally, and this might be unconnected with the fault but after a while I'm wondering if there is a link. I currently disconnect the battery fro a day or 2 if I don't have time to trace the starting fault. When I reconnect the battery the window switches are reversed as the pass. switch operated the driver's window!
Please let us know how you get on and I will add anything of interest that I find. By the way do you get any error messages o the dash display?