Assuming you've checked that there's nothing obvious that may have been disturbed during your procedure, here's stuff to check but before you do, get a good strong battery on it or jump leads from a running, charging vehicle and try it. I've had the scenario a few times over the years with the 480 where battery is strong enough to crank the engine but voltage drops too much for the ECU's so no go. A good battery should crank like the clappers for longer than 10secs, seems like this is likely. If this still doesn't work then try some of the following-
To check spark, take the king lead off and shove a spark plug into it, allow the plug body to earth somewhere and get someone to crank it, make sure the plug is sparking. Bear in mind, even if there is a spark, it might be weak and unable to ignite the mixture under pressure in the cylinder but if the car was running ok minutes before then this may not be as likely. If you have spark then your crank sensor is definitely ok and coil most likely ok. If no spark then could either be crank sensor or coil or ignition relay, the next bit may help you eliminate/diagnose crank sensor.
There's two relays that come off the jetronic loom under the dash up next to the steering column somewhere, these are fuel pump and ignition relays. There are fuses alongside the relays in the sockets, check these and check the function of the relays (if you have spark then you can rule out the ignition relay and fuse). Hold them in your hand and turn the ignition on. One of the relays should click, energising the ignition system. The fuel pump relay will only become live when the fuel ECU detects a speed signal equivalent to 50 rpm (IIRC) so the second relay ought to click when the engine is cranking (assuming it's cranking well with good battery voltage). Also, on the subject of voltage, I think the ECU's need a good 10v or so minimum to operate so make sure the battery is strong as a weak battery may drop too low under cranking load to energise the ECU's. If you happen to find a scenario with no spark AND no click from the fuel pump relay during cranking then this points strongly toward crank sensor (remember about the speed signal requirement for the fuel pump?). If you do have spark but find that the fuel relay is not behaving correctly then this is the next thing to investigate, could be a faulty relay or a break in one of the circuits. All this you can do with no tools, next, get your spanners out....
Easy way to check actual fuel delivery, either disconnect the fuel line from the rail and put it into a container, crank the engine. Fuel should piss out at quite a rate. Or... take out the plugs, crank it and sniff the cylinders for the smell of fuel. You may even see fuel mist coming up out of the spark plug bores. This will eliminate injectors as a problem too if there's fuel getting as far as the cylinder. If this is the case then it's definitely an ignition problem or major engine mechanical defect (seems unlikely so ignition realistically). If the fuel relay is operating correctly, next stop is checking actual fuel delivery as described above. If the relay operates but still no fuel then could be pump or wiring maybe.
Also, easy way to rule out ignition problem is to spray easy start, brake cleaner etc into the intake, crank it and see if it splutters or runs for a second. If it does then obviously ignition is good and it's a lack of fuel causing the issue.
There's not really that much more that would stop it running, remeber, fuel+air+spark = go! Start with spark, then look at fuel, air is kind of a given, although I suppose if you had a faulty idle valve you would need to have throttle open a bit but I suppose you've been giving it throttle anyway, I know I always do when something won't go
This is not an exhaustive guide to every possible non running scenario, obviously, however I've listed all the things that would be my first checks in a non start situation. If still no joy after checking the basics, let us know how you got on and we'll try and help. Good luck, and try not to get frustrated, stay cool and be methodical and you'll find the problem, there's not that many things on these cars that can stop it running assuming (fairly safely I should think if the car was running so recently) that the ECU's themselves and the loom are fine.
O.C. 480 D.
