Another Hard Start Q?

[Labyrinth]

The truck - '98 GMC Sonoma SLS, 4.3 Vortec

The trouble - Hard start when cold (that is parked for 4 hours or so). I turn the key to run/acc, let the fuel pump cycle. When the pump turns off, I turn the key to start. It will crank for 4 to 5 seconds before a very rough start.

Something I've noticed - I can get the truck to start "normally" when cold (again parked for 4 hours or so) by doing this; Turn the key to run/acc, let the fuel pump cycle. When the pump stops, turn the key to start for a second, let key go back to "run/acc". The truck won't start and the fuel pump cycles again. When the pump stops, I turn the key to start and walla .... engine fires up like brand new.

Anyone know what repair fixes this?

Thanks in advance

[Sparky2263]

Definitely a fuel supply problem. Most likely filter and/or pump. A fuel pressure test would reveal the problem.

[Labyrinth]

I guess i should have mentioned that the fuel filter has been replaced.

Why should I suspect the fuel pump when I have no problems when the engine is started or when the engine has been off for a short time?

[Sparky2263]

The ECM provides a 1-2 second "prime" shot of fuel when the key is cycled on. If it doesn't get the "prime" shot, then cranking times will be prolonged as the oil pressure switch has to close in order to operate the fuel pump. Also, the pump could be weak.

A fuel pressure test would reveal either problem.