Common problem with a twist
 

1997 Cheyenne 4.3L V6, 162xxx miles.

Commonly, when there is a low fuel pressure situation, an engine can be difficult to start since there isn't adequate pressure to feed the FI system. My pickup is acting like that, but with a twist. First thing at 5:30 am and I'm headed out to go to work, no problems. It starts right up regardless of any variable. But just over 8 hours later when it's time for me leave work, it acts like it has no fuel pressure. At that point, I have to crank for 15-20 seconds generally. Once it's running, the engine behaves perfectly, idling and accelerating well. The sending unit in the tank was replaced at about 100K miles, so it's not original. Earlier this week I changed the fuel filter just to eliminate that as a problem. One thing to note after changing the filter and losing all fuel pressure, it took less cranking time to get it to start then -8 to 10 seconds- than it does when I'm leaving work. I've wondered about a faulty fuel pressure regulator, but that normally results in excessive fuel going to the engine, not insufficient fuel flow(at least in my experience).

I am absolutely stumped. Any thoughts are appreciated.

can you put a fuel pressure gauge on it to see whats is going on pressure wise? which i mean is a after market type mounted on the hood for now till you find out whats is going on. so this way you can watch the pressure all the time

I'm not one to drill holes in the sheet metal. I found a way to brace up a handheld gauge under the hood. I'll check it before starting the engine to see what's happening, and report back in a few days.

well i should have said to tie it down with like zip ties if there is a place to do that on. or even tape it on for just now so you can see whats going on with the pressure.

Here's what I can tell for certain. After sitting for a couple hours, the fuel pressure is dropping to about 22 lbs. After turning on the ignition but not starting the engine, pressure jumps to about 55 lbs. That much does not change, regardless of time of day. In the mornings, it starts right up every time. In the afternoon, however, sometimes it will start right up and other times require long crank times.

At this point, I'm completely befuddled. How does my truck know what time it is, and why it trying to strand me at work? ;)