Working on a 1990 7.3 IDI, bought the truck suspecting a bad lift pump. After fixing leaking O-rings on injector returns and fixed leaking fuel filter housing, I hooked a temporary electric pump to test engine before I buy a lift pump. I have a clear return line to the filter housing. The clear doesn't even begin to clear up, it is full of air and it doesn't seem to ever fill up. I purged the injectors for a while, I purged the air in the filter. The electric pump puts out about 6psi, but it almost seems like the fuel is going some where, but I don't see any leaks. Any ideas? Thanks

 

Run the output side of the pump into a bucket. You may be sucking air into the electric pump.

 

that is what it sounds like to me also. either a hole in the fuel line, cracked pickup in the tank, or an empty fuel tank.

 

Looks like the small electric pump I was using was sucking in air or something. I bought a new lift pump and the truck started right up. Thanks