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?

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.

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?

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.
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Chevy Silverado Hard To Start- Fuel Pump Replaced