My 81 928 has fuel,pressure and spark but will not run
 

I have gone through the systems and have pressure, the pump runs the regulator and bypass are new but the engine only runs if I put primer in the air intake. Is that a relay issue or something else? It started out failing to start on a couple of drives. I released pressure from the fuel rails while checking for fuel pressure (parking lot at grocery store)and it would start. Now it won't even start unless primed and it will run for about 20-30 seconds once primed. Then it just stalls.

check compression

similar issue happened on a local 928 here in Austin and it turned out to be a dislocated camshaft.

mike

welcome to my world I have same year with same problem replace fuel injector relay found mine on ebay 14 bucks ordered monday came thursday was driving friday morning

another thing to check is make certain the WUR (barndoor) sensor is properly down in its o ring. It is pretty easy to not seat it properly when placing the lower half of the air cleaner back in the car....the WUR tells the computer it is closed as there will be little or no vacuum and there fore does not fire the injectors. Prime it and it will run for a bit. Don't ask me how I and a buddy learned this, the very hard way....

Try spraying in a good dose of starting fluid, see if it will idle. If it will, your injector computer is not functioning. May be a loose ground on the pax valve cover above the letter "O" under the supplemental air valve. Very hard to see. If loose, I recommend relocating it to the forward hole on the same valve cover, that way you can actually see it for inspection later.

That is, if your model is like my old 82.

FWIW since you have already figured out the part to make the car run is fuel,
dont spray more flammable liquid into the intake to test it.
From the info provided,
first replace or swap the relays as this is usually the issue,
next would be a failing fuel pump ,
also the green wire is suspect if its original