When I leave my 97 Chevy 1/2 ton for a few days
the damn thing don't want to start. Cranks like all get out. No starty.
Eventually, after 5 or 10 minutes of crankin and waitin, it will start.
After that, starts fine all day long.
Today when I tired to start it, nothing for maybe 5 minutes. So I pulled
the intake off and poured a little fuel into the throttle bore and it
fired and died. Poured a little more in and it fired right up and ran
great all day.
I checked the fuel pump pressure and that's fine. Put a new filter on a
few months back.
Is there some kind of one way valve that might be bad, allowing fuuel to
bleed back down? Or something else I'm not looking at? It must be a fuel
delivery problem, but only on the first start after sitting a couple of
days. I'm stumped.
350 5.7 auto 4x4

Borked Psuedo Mailed wrote:
When you first turn the key (ON not to start) do you hear the fuel pump
turn on? It should turn on for a couple seconds and then turn off.
If it isn't then check the fuel pump relay.

What normally happens is you turn on the key, the pump turns on for a
couple seconds to pressurize the fuel system. The engine then starts and
the computer then looks at the oil pressure sensor to see if the engine
has pressure. If it does(takes about 5-10 psi) it turns the pump back on
and keeps it on until you either turn off the key, the oil pressure
drops to zero, or the fuel line/pump system fails.

The back-up to this system (in case the relay fails for some reason) is
that the oil pressure sensor also supplies power to the pump.

Wiring colors at the relay-

Red - Pump prime (connect 12V here to bypass the relay and test the pump)
Orange - Power into relay
Gray - Wire to pump
Dark green/white stripe - Relay control from ECM
Black/white stripe - Ground for relay.

Wiring at oil pressure switch -

Body - Grounded to engine
Tan - Pressure signal to ECM/Gauge
Orange - Power into switch
Gray - Power out to pump

Wiring at pump -
Gray - power into pump and sender
Dark Blue/white stripe (or purple on later trucks)
Black/white stripe - ground to vehicle frame

--
Steve W.

There is a check valve which prevents fuel from flowing back into the tank.
A test for this would be in a GM factory service manual set for your
year/model vehicle.


"Borked Psuedo Mailed" wrote in message

On Wed, 30 Sep 2009 00:39:37 -0400, "Steve W."
<csr684 (AT) NOTyahoo (DOT) com> wrote:

I just have to jump in here and say that's a prettyt awesome
design.


--
http://desertphile.org
Desertphile's Desert Soliloquy. WARNING: view with plenty of water
"Why aren't resurrections from the dead noteworthy?" -- Jim Rutz

Steve W. wrote:
Yes, pump is turning on, then off after a couple of seconds.
Oil pressure reads OK.

Pulled out the relay today, then plugged it back in. Turned on the ign
switch, could hear fuel pump cycle, then turn off. Pulled out relay
again with switch still on. Plugged it back in. Heard and felt nothing
inside the relay. Also, fuel pump didn't cycle again. Could the relay be
bad?

Still no start until I pour a little gas into the throttle body. Then it
fires right up and runs/starts fine all day long.

Weird. This thing is driving me crazy

Borked Psuedo Mailed wrote:

The timing is controlled by the ECM, It will only cycle the relay when
the key is turned off/on. That starts the timer.

What I would probably do is let it set a couple days, till it won't
start. Hook a fuel pressure gauge on it then turn on the key. See what
you get for pressure. If you have good pressure then BUT no still no
start then I would check the connection to the injector harness and
stick a couple noid lights on there to see if the injectors are firing.



--
Steve W.

Steve W. wrote:
Steve,

Is there a pressure regulator or one way valve in the fuel line that
might be leaking fuel back into the tank after sitting overnight? What I
can't figure out is, why will it start if I dribble fuel into the
throttle body, and will start fine once it's been running for a few
minutes and start fine the rest of the day, but only on the first start
from sitting will it not start. I hate having to take it to a shop to
figure it out.
Thanks to everyone for all the help and suggestions so far.

Borked Psuedo Mailed wrote:
There is a pressure regulator on the line. However if it is leaking down
like that it likely wouldn't hold pressure any other time. So you would
have to keep starting it with extra fuel each time. There is also a one
way valve on the pump itself. It is easy to test.

See what the pump is doing. If it comes up to pressure fast and the
system test for the regulator is OK, run the leak down test (basically
you get the engine running, then shut it down and watch the fuel
pressure) There is also a check like that for the pump.

--
Steve W.

On Thu, 01 Oct 2009 13:22:22 -0600, Desertphile
<desertphile (AT) invalid-address (DOT) net> wrote:


It is. But it's been around for a while. My 92 Explorer has the same
setup and I'm sure it's not original with it.