Chevy Silverado Hard To Start- Fuel Pump Replaced

2000 Silverado Z-71. Engine size = 5.3
Repair done prior = Tune up at 100K with new fuel pump/sending unit. Work done to repair this problem = New fuel filter. New fuel pressure regulator. Throttle body cleaning. Air filter (K&N) cleaned and re-oiled. Fuel injector cleaner additive.
Question = Truck suddenly became hard to start. Used to start when you touched the key and in 1 day it began to crank for a long time prior to starting. Turning key (fuel pump) on and off 2-3 times before cranking seems to help allot. Fuel pump was replaced during tune-up at 100K. No notable vacuum leaks, pressure regulator replaced with no change. Mileage has gotten considerably worse, especially when towing. No codes displayed at all. Plugs replaced at 100K were OEM Autolite. Any ideas before I drop the tank again?

Answer:
The fact that this problem started all of a sudden, and the turning of the key a few times to help it start does make me think a fuel pressure problem. It is possible that the connector on top of the fuel pump assembly has a burned terminal. This would cause low fuel pressure because of the high resistance in the fuel pump power feed circuit. That would explain the hard starting, but not the poor economy. Suggest having fuel pressure checked. Should be at least 55 PSI. Even 2-3 lbs. less can cause this concern. This 5.3 engine is also known for the intake manifold gaskets leaking vacuum. This causes a hard start and also high idle in cold ambient temperatures, as well as hesitation off idle and unstable idle when engine hot.

I would also check those Autolite spark plugs since they have been in there for about 30k miles. Have seen many times non AC Delco plugs cause odd problems.

VISITOR REPLY:
First, let me say that the truck is running smoothly and there is no hesitation during acceleration at all. I hooked up a pressure tester: With the engine running at idle (hot) I’m reading approx. 48 PSI. However, if I take the vacuum hose off the pressure regulator it jumps up to about 58/59 PSI. This is a brand new pressure regulator.

I also noted that as soon as I shut off the engine the pressure on the gauge dropped very rapidly..not instantly, but very quickly, down to around 10 PSI and then very slowly bled down from there. So I’m thinking that since the pump is capable of pumping 58/59 PSI (with the regulator disconnected) then the problem must be elsewhere. Maybe the new regulator is bad? Maybe a leak in the system? Any thoughts on this?

Answer:
Do this...
With pressure gauge on, turn key to RUN. Pressure should go to at least 55 psi and hold. Sounds like it will not hold.

2 possibilities...
Check ball in fuel pump is stuck and allowing thew fuel to bleed back, or maybe the tiny little O ring on the tip of the regulator rolled when installing the part. Or the old O ring is still in there. Remove it and check the O ring. We use shut-off valves to restrict the feed and return lines one at a time to determine which way the fuel is draining back.

Question: My 2000 Chevy Silverado that will not start unless i pour gas in the throttle body. It has been sitting for about 8 months and prior to that there was no problems at all. I have good fuel pressure with no bleed down.
 Answer: Does it start after pouring gas in throttle and keep running fine? What is the fuel pressure?

Yes after i pour gas in it it will run and drives just fine with no missing or sputter or anything the pressure is 54 psi and it runs at around 50 to 52 PSI. This is the same exact pressure in my other truck with no problems and a new pump. The truck 2000 only has 28000 miles on it.
 These trucks are very sensitive to fuel pressure at Key-On. A little below 55 PSI and they wont start. With is sitting so long, the slightly low fuel pressure may be aggravated by sticking fuel injector nozzles.

I thought about that too but it runs perfectly even driving down the road when you step on it there is no hesitation what so ever. If i had bad injectors it seems there would be some kind of hiccups. I did have 1 code that said system too lean bank one,but put on a computer and both 1 and 2 read the same. 4.3 v-6.
 OK. The injectors are no really injectors, they are poppet nozzles. The reason these motors don't start with less that 55 psi is that it is not enough pressure to pop them open. But, once running, they will run fine.

It just seems like 1 psi less shouldn't be a big deal, but i understand what you are saying. But maybe i do have a bad 1 or maybe a couple poppets the are bad, but how can i tell without removing the intake to get to the spider assembly?
 Most of the time it is not the injectors that cause the problem, but a weak fuel pump or restricted filter. Try cycling the key a few times to see if the pressure goes up a little.