My S3 XJ6 won’t start. I replaced a faulty injector and took it for a drive. It ran well and I was happy with the world. The next day it would not start and hasn’t since. I need help please.
It has fuel to fuel rail at about 100psi.
It has spark and cranks over well.
Relays seem to be operating.
Checked most things including trying another ECU without luck. There is power getting to the ECU from the coil.
Found that there is no signal to injectors when cranking. So think this is likely reason.
Also checked most connectors and earthing points.
Have not checked Air Flow Meter.
Has anyone had this problem or know of a solution?
That’s the raw “deadhead” fuel pressure? If so, that’s good. But regulated pressure should be about 36 PSI.
If your regulated pressure is 100 PSI that’s way too high
“Seem to be” isn’t very reassuring 
For the moment your focus should be on the “main” relay which powers-up the ECU and supplies voltage to the injectors.
The solid brown wire should be 12v at all times. Black should be ground. White wire and brown/slate wires should be 12v with the key ‘on’.
Assuming the relay is good check that the voltage on the brown/slate wire is making it’s way down to the injector resistor pack…and check the connector for cleanliness. The resistor is on the RH inner fender, low and forward, roughly across from the p/steering pump.
I presume you mean the ‘trigger’ signal from the coil “-” post on the white/black wire running aft along the water rail, yes?
Have you specifically checked the bundle of ground wires at the rear of the water rail? There are 5 or 6 of them. The entire fuel injection system grounds/earth here.
Given the sequence of events go back and carefully retrace all your steps, again. You may have jiggled something loose or broken a wire. That’s not a criticism; it happens to everyone from time to time. The wires and connectors are often brittle from heat and age and will break if you so much as look at them angrily.
Cheers
DD
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As Diug says; verify that the ‘main’ relay is operating, David - without power from the relay; the ECU is dead…
Also; the relay also powers the injectors via the injector resistor pack. Disconnect an injector connector and check there is 12V on both wires - no power, no injector action. Failed relay likely…
The signal from the coil just triggers the ECU to briefly ground one injector wire - opening the injector…
Frank
xj6 85 Sov Europe (UK/Z)
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Thanks Doug and Frank
Your comments were very helpful and I put them to good effects with a friend (ex mechanic). I now have a xj6 S3 that runs even if a little rough (rich).
Found there was no power to the main relay and also no signal when the ignition switch was turned on. Found the diode pack was faulty when replaced the main relay operated. Started car by running a wire from battery directly to the main relay. Then had to find why no power to the relay. After much searching found the brown wire near the battery was not connected (a lose fit). Plugged it back in and got power to the main relay. So simple in the end.
I’ll take it for a run after checking the fuel pressure regulator. Hopefully after a gentle drive it’ll run a little better. I will post an update when done.