Recently had several days where 5.7 TBI engine will not start when hot. Found it to be a fuel problem - as in none getting to TBI. "Hot" means drive for 1 hour in 90 degree weather (Connecticut). Question is: When using the fuel pump test circuit by applying 12 volts, should the fuel pump run regardless of other conditions or settings? And, if it does not run when hot but does when cold (or cooler - as in wait 3 hours), does that indicate a bad pump? The pump is exactly 1 year old (give or take a week). Can anything else in the tank be at fault, since the pump is kind-of new?
Thanks in advance for any ideas.
Dave.

If the test bypasses the fuel pump relay, yes, it should be running full time. The regulator will manage pressure, and the pump should be running.

I don't have a 93 FSM, but if you do, look at the wiring diagrams on the fuel pump relay and see if there is anything else in the circuit AFTER the fuel pump relay and if the test does short the +12v to the pump direct.

Just because it is a year old doesn't mean it is good. Some cheap replacement pumps are crummy and don't live long. Don't rule it out, but it is a smaller % that that isn't the issue. But it could be.

Try this. When it fails, is there a full tank of fuel? Or low on fuel? A 1/4 tank of fuel will be much hotter fuel temp than a full tank (which will take much longer to get warm) and will have the fuel pump itself much hotter.

If you know when it regularly fails, ensure that you are getting it to fail at a gas pump. The tanks are underground and fuel is around 60-65F. MAYBE as high as 70F. Fill 'er up when you confirm the failure mode. Then see if it starts right up. If so, look at the pump.

Thanks for your reply. As I read the SM, it looks like nothing else is in the circuit. I am quite convinced it is a defective pump as I think you are, just seemed hard to believe at first. I did once hear that idea about the cooler fuel from the station, but failure is so unpredictable, I can't be sure I will be near one. I thought the pump I got from NAPA might have been of good quality. Even though it is a pain in the ..s to change it, I guess I will do it again. I was hoping to hear from someone who may have had the exact problem. I needed that mental confidence that another pump change would end my 3 hour waits for cool down.

Thanks again for your ideas.
Dave.

Well, I sorta had the same problem, but on a 91 Bonneville. It would do it on 90+ days when the tank got low, like on a trip. It got bad enough I almost got stranded in St. Louis. Was able to cost off the interstate to a gas station, filled up and power was back and it ran fine. So we stopped for lunch and killed an hour or so, and the problem went away the rest of the trip. But as time went on, it was more and more temp sensitive until I HAD to change it. It sucks, I got 2 maybe 3 years tops on my NAPA fuel pump. And the "new" one (the one that failed in 2-3 years) was noisy for a long time, once it got quiet, it was starting to fail. I put a pressure gauge on it and it was low, 20-30 psi. Enough a 3800 got crabby about it.