97 Chevy cold start problem

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
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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.

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On Wed, 30 Sep 2009 00:39:37 -0400, "Steve W."


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

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On Thu, 01 Oct 2009 13:22:22 -0600, Desertphile

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.

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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
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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.

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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.
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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.
--
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Steve W. wrote:

Re tested the pump this morning.
48PSI with key on, no crank 40PSI during cranking.
Book says should be 55-60.
Would that slight amount of lower pressure result in a no start?
I'd hate to have to drop the tank and throw in a $300 fuel pump over a 10-15 PSI differential if that's not the problem, but nothing else is looking good.
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Borked Psuedo Mailed wrote:

Yep, That is enough to cause a problem.
I would test the regulator and test the pressure against a dead end first though. It is possible that the regulator is faulty and letting the pressure drop off early. There are a list of tests in the book. Easiest way on the pump is to pull the line from the pump and see what it reads with a gauge on it.
When was the filter changed last?
Or you can shotgun it with a new pump and regulator.
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Steve W. wrote:

Replaced the filter 2 months ago, so that's not it. Since the pressure regulator is attached to the pump, that means I gotta drop the tank anyway I look at it, and with the tank down, I might as well just replace the entire assembly. The truck has 304k miles on it and I'm not sure if it is the OE pump or not, but it doesn't make sense to take chances. The 1 chance I am going to take is with an aftermarket pump. My parts guy says he hasn't seen much of a difference in bad replacements between Delco and the aftermarket in tank pumps, but there is a huge difference in price. I can get an aftermarket (Carter) pump off Ebay for $75, while a new Delco is almost $400. Even Autozone wants almost $300 for their aftermarket pump (airtek), so for the $75, I figured I'd take a flyer. Of course, it never fails. I just filled the tank day before yesterday, so now I gotta borrow a few 5 gal jerry cans and pump all 20 gals fuel out before dropping the tank. Thanks to everyone so far for all the help and direction. I'll let you know how it works out.
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Borked Psuedo Mailed wrote:

Pressure regulator is on the fuel injector assembly inside the intake plenum. There is a prescribed way to test it.
I would run the tests first. It will show you if it is the pump module or the regulator.
As for a new pump, I would try RockAuto.com They show a Delphi pump ONLY for 74.00. That doesn't include a sender or the filter sock.
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Steve W. wrote:

Steve,
I already ordered the fuel pump assembly off EBay, but looked at the Rockauto site you mentioned. They don't show a fuel pump only, or I'm not looking in the right place. I bought the entire assembly for the same price as the pump alone. Hope it works. When we tested the pump pressure this morning, I believe the pressure test point is before the regulator in the plenum, so the 48/40psi we got means the pump is weak anyway. In the event the new pump doesn't sure the problem, I'll replace the regulator too, but I'm hoping the pump does the job. Now I just have to go to the neighbors house and borrow a couple of jerry cans.
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