Purge valve ?

 

I thought about that, but with a bad valve it would still stumble or even run poorly. I can't even hear any combustion at all.

 

TB - Do you hear it humming when the ignition is just "ON" (no cranking)
Spark - If the spark is weak you can see it but it will not ignite the mixture
Injectors - There's always some kind of smell from the cylinders when you crank the engine with the spark plugs removed. Do you get strong fuel smell from the exhaust tips after longer cranking?

Since the car has sat for 7 years, there might be some corrosion on the pins of the relays for the above three functions so it is a good practice to check and clean them and also bench test every relay for correct operation.

 

Update:
@M. Stojanovic, Yes the TB hums, and yes the exhaust smells of fuel.

Alright, I built a tool to direct the oil going into the cylinders, and I put just a bit more oil in each cylinder radially. I tried cranking, still nothing.
I then pulled all the plugs and cranked it for awhile multiple times just in case the plugs were fouling. Threw it all back together, still not starting.
I compression tested each cylinder, and it looks like it's improved slightly:

Driver's side front to back:
100 psi
100 psi
100 psi
70 psi
Passenger side front to back:
90 psi
90 psi
100 psi
80 psi

To my knowledge, this should be enough to fire, but it still just cranks (starting fluid doesn't help either).
So I know it has compression and air, I know it has spark when tested outside the engine, and I know it has fuel. So one of my assumptions must be wrong.

My best guess is that my assumption that the fuel it's getting is good is wrong. I wonder if that first fire ran on the fuel in the lines between the filter and the injectors, but now all the fuel that's getting to the engine has now passed through this filter that's sat for 7 years. I've noticed that most of the plugs after an attempt are wet with what looks like dirty fuel (although it could be dirty oil).
To me this means that the injectors aren't clogged, so just swapping the filter should be an improvement, so that's what I'll do next. I tried using plenty of starting fluid through the throttle body, but it didn't make a difference, though I now assume that it doesn't work through the supercharger.

Thank you all for the continued support, and any more ideas or advice are welcome.

 

I am going through the EXACT SAME situation as you right now with a 2003 XJR and I also tried everything you have tried.... unfortunately, I have had no success.

 

Just spit balling but have you guys tried a hard reset? Whenever my XJR acts strange (No start, rough idle) with no identifiable mechanical or electrical problem I hold the negative battery cable to the positive terminal for 30 seconds and it forces the ECM to reset. I've also had good results after changing the relays, far fewer issues. This may be useless in this situation but it looks like you've tried everything else.

 

if all else fails dump fuel into the throttle body

 

I was not aware of the ECU reset procedure, I'll have to try that. While replacing the fuel filter, the fuel line broke from rust, so I'm in the process of replacing it, then I can try the reset.

 

Is there a possibility that rusted line was cracked and you were losing fuel pressure?

 

I'm going to suggest that you revisit your spark assumptions. Sometimes you can get visible spark outside the cylinder, but under compression, it's not strong enough to ignite the fuel, as someone suggested above. I would replace the ignition coil relay even though you have visible spark. Even if the new relay doesn't solve it, I would stay on the spark issue. You have compression and fuel, so it has to be spark. Something is different between your visible spark test, and when you thread the plugs back in. The spark is too weak, in my opinion, once you thread the plugs back into the cylinder. That could be the plugs themselves, or the voltage coming to them. It's not likely that all 8 ignition coils went bad at the same time, but keep digging on the spark question. My money is on that.

That said, I assume that you have new fuel coming to the injectors, right? You cleaned out the old fuel, not only from the tank but from the lines too? If the answer is yes, then it's the spark.

 

The line was holding pressure prior to the replacing the filter, it was 45 psi at the rail.
Yes, the fuel is new, as are the spark plugs with the correct gap. A relay simply transmits power does it not? A bad relay would mean no spark at all in or out of the cylinder.

 

Generally yes, but not always. A bad relay can send insufficient voltage through to the coils. For the few dollars it costs, I'd still recommend changing it. Or at the very least, rob a relay from another socket to try it quick to see what happens. It has to be spark related.....