You can find info on testing relays here: http://www.backinblackgp.com/

I swapped out the relay yesterday and still having starting problems. It started this morning. Had to shut van off for about 5 minutes and then it wouldn't start again. It started up about 5 minutes later. Puzzled!

check out the relay socket try to pry on the pins carefully so the relay pins fit tighter and inspect for corrosion

I'd look at the fuel pump and the fuel pump ground. Had a similar problem on my Son'* S10. Ended up being a frayed fuel pump ground wire. It was barely making a connection, let the truck sit a while longer and it would start. Took my six weeks to find the problem.

You could also have a fuel pump problem. You need to do a pressure test when it is failing. The tool is around $30 if my memory serves me this morning.