87 XJS, won't start. Here's what has been done so far and what I've tried. Over the winter, new plugs, wires, cap, rotor, fuel injector hoses, vacuum advance unit. Car started right up and ran good afterwards. Put plates on as I don't drive it over the winter, first drive, no issues. Second trip out, started up and ran, stopped for fuel, would not start afterwards.
When you first try to start it, it fires a couple of times but won't start and it will repeat this after you let it sit for awhile. Installed a fuel pressure gauge before the "out" regulator, 36 psi and it holds. With the ignition on, opening the throttle causes the injectors to click and the needle on the pressure gauge to drop slightly each time you do this.( pump not running).
If i remove the fuel pump relay, the fuel pressure gauge doesn't drop while cranking the engine, injectors not firing? Check the spark, has a good strong spark. Checked voltage at coils, 12.3 volts. Checked the resister for the feed to the ECM, checks out, 6.7 K ohms. Checked the shielded wire for continuity, 1.2 ohms front to back. Checked the wire to ground, checks good. Unplugged the harness from the computer and checked the coolant temperature sensor resistance, about 2.5 K ohms from that end. Cleaned the connector to the resistor pack and checked the resistors, all seems good. C

omputer? New to this Jaguar thing, looking for fresh ideas.

 

My thoughts.

Lucas cars have a few common issues.

That shielded wire is suspect, I KNOW you tested it, and the numbers a low, I prefer closer to zero. Soooo, the fiddle factor, thanks to Doug, kicks in, reach down the back of the engine, that loom is there near the heater tap, CAREFULLY, move it around, dont be stupid with that fiddle. Try again. If that works, chances are the shielded wire is the issue. If no change at all, read on.

There is a wire FROM the starter relay TO the ECU, that "kick starts" the Injection PULSE circuit during cranking, coz the pulse in that shielded wire aint there yet, and that sounds like its missing. Pin 26 of te chart attached. I know that chart is NOT for your market, emissions crap we no got, BUT, the basics are identical.

ECU failures, never had one. The 6CU had its issues, but generally did well. The 16CU, unless Danny Dropkick did something real stupid way back, I seriously doubt it.

Earths, BORING, but they reek havoc now in old age.

I can no longer read wiring diagrams, so someone else will need to chime in if needed.

 

Further to Grant's vital points:

1. Are you sure that there is a strong spark while cranking ? Test for this by, (a) disabling the fuel pump and (b) removing a plug and having someone look at it (while earthed against the engine) as you crank.
2. If it is sparking while cranking, is there fuel actually spraying into the intake? The best way to check is (a) remove the king lead from coil to dizzy and then (b) undo the retaining collar on the front A bank injector and pull the injector out, still attached to its flexible and point it into a jamjar; then ask someone to crank the engine while you look to see if the injector is spraying.

The fault has to be caused by one or the other of these two systems not working. Report back with your findings and further diagnosis starts there.