91 4.9l doesn't want to fire when cold?

I've been having trouble with this for quite some time. When I first bought it (used in 98), every once in a while it would not start. I discovered if I turned the key on for a few seconds, turned it off, then back on - doing this several times, it would start (though I'm inclined to believe now that only the key on time was helping). Over a period of time it got worse. I would have to hook a battery charger/booster to it and crank and crank and crank. Finally it would start.

Replaced the fuel pump (which I really thought was the culprit), filter, and pressure regulator. Replaced plugs, wires, rotor, dist cap, and coil. Put a new battery on it the other day. I discovered that if it doesn't start, just leave the key on for sometimes a minute, sometimes several minutes, then it will start like nothing was ever wrong. :screwy:

It seems to have something to do with the cold start mechanism (I think), but I don't know what kind of mechanism it uses, or where it's located. Anyone with any advice or info please sound off. I'll listen to anything. :banghead:

Sounds as if you might have a fuel pressure leak down problem. It could possibly be a bad injector or more.