Difficult starting

I have a 1998 S-10 king cab 4 wheel drive pickup with a 4.3 liter engine with 258000 miles. When the truck sits over 8 hours, it is very difficult to start. After it starts, it runs very well and will continue to start normally if it does not sit without running for more than 4 hours. It has plenty of power throughout the RPM range up to 4500 rpm, and still gets better than 20 mpg on normal driving. My mechanic said the fuel pressure is within limits. Any ideas why this occurs?

The next time you go to start it after it has sat for an extended period of time, turn the ignition switch to the run position so that the dash lights come on for two seconds, and then turn the ignition switch off. Repeat this a half dozen times and then try starting the engine. If the engine starts right up the problem is with the anti-drain back valve in the fuel pump assembly.


I asked my mechanic about this. It seemed too me that there was no gas until it “worked its way up”. Your answer makes sense and I will try that.
Should I replace the fuel pump, or just not worry about it?

The fuel pump is working fine when the engine is running. At 258,000 miles, why change it? You have a viable work-around (on, off, on, off), now, for priming the fuel pressure at the engine.
I believe that there are anti-drain-back valves that can be installed in the fuel line, if desired. Check jcwhitney.com.
If the fuel filter hasn’t been changed in recent memory, now is the time to change it.

I replaced the fuel pump 2 years ago and the fuel filter end of July of this year. This problem reminded me of the carburetors when the needle and seat went bad and had to be replaced.
thanks for your help!