I have a 2003 E150 with the 4.2L, and it occasionally has a really rough start, or it just refuses to start. I sometimes have to crank it for a while, and when it finally catches, it stutters for a couple of seconds, almost stalling,and then it runs fine. Once I get it running, it runs great, even going 70 mph down the freeway.

It occasionally just refuses to start, I can crank it for several minutes, and it won't fire once. I once took out a spark plug when this was happening and cranked it, and the cylinder was completely dry. Whenever this is happening, I can disconnect the fuel line at the manifold, hook it back up, and it will start on the first try, guaranteed. I already replaced the fuel regulator (didn't help), and the vacuum line to the regulator has vacuum.

If anyone knows what's broken, or even some theory on what's going on, I'd appreciate it. I don't like to blindly replace parts, but I'm at a loss.

 

put a fuel pressure gauge on the fuel rail, pressurize the fuel rail and watch for pressure leakdown.