I would suggest you do a search through no start threads so you can see what the no spark or weak spark possibilities are. As others have said it is the most likely senario.
Also when you do find the problem then update this thread with what the problem was so you are helping someone down the line.

 

No spark is almost definitely the problem. The previous suggestions to check an individual plug spark are valid, but not true if there is a bad wire to that plug. I would look at the distributor control circuit. Maybe something simple, like the connectors ate the back side of the distributor, or the connection to the fuse panel under the dash. (been there, done that, no T-shirt). Good luck

 

If it has fuel does it have any spark?

 

^^ Perfect ^^

 

You need fuel, spark and air....You said its got fuel, air shouldn't be a problem, so I'd look at spark. I use my timing light to check that, simply connect it to any plug wire and spin it over to see if it flashes. If it doesn't flash, I'd probe the 12V ignition source going into the HEI with a test light and be sure you get a light with the ignition key on and again when the key goes to the start position. If that checks out, I'd suspect the HEI module and/or the coil is done and needs replaced.

 

Pull a plug and make sure you're getting a spark. If you're getting gas it has to be it's not getting spark. As OLDED said you may want to make sure you're getting a full 12 to the HEI unit since for a normal coil the voltage steps down after the car starts (i.e. full 12v during starting but when the key goes to on the voltage is reduced). So if you used the normal wire that would go to the coil to go to the HEI, it will have reduced voltage when the key is in the on position. This in turn could have burned out the HEI module.

 

I thought I was pretty clear. Last time I drove it about a week ago and all the times before that it ran great. The car has not been started since then, so absolutely nothing changed. It has gas. The whole car has been rewired with an AAW Classic Update kit (so dist has full 12v). All it does is crank & crank & crank, no start.

 

Check/exchange the Ignition Control Module. what year is the car - older years run the ignition hot wire through a firewall mounted "ballast" which reduces the voltage to 7 or 8 volts which does'nt work with the HEI setup. If it has the ballast - bypass it and send 12 volts to the distributor.
At least check for 12 volts at the distributor ht wire.

 

I'm not sure I understand. Your first statement is that it runs great. Did you change something since it was running great? Does it start, or does it try to start but won't run, or ? If it has gas but doesn't fire at all then it's more than likely the ignition. If it tries to start but won't run then timing is probably the issue. Again without more information we're shooting in the dark.