Bus works with engine cover off but not when it is on

[rideordie]

Hi everyone, I have a 1991 Chevy G30 Bluebird school bus. 5.7 L engine. 4 window gasser.

Recently it wouldn't start. For a few days or maybe weeks prior I could feel some hiccups as it idled so I was fearing the worse. Then it stopped completely. With the help of some internet friends, I was able to trouble shoot it over 24 hrs and get it running.

What I did:
- checked that there was spark to ensure there was no ignition problem
- changed the fuel pump relay <--- this seemed to fix the problem but ...

When I put the bus back together and covered the engine (it's one of those where you also have access from inside the cab by the driver seat), the bus would not start. I had the remove the cover to drive it home.

Anyone had this experience and can point me in the right direction? I am hoping it isn't a fuel pump problem.

Thanks!